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The thread about the USMC battalion experimenting with suppressors got me thinking.

What are the differences, if any, in accuracy between say a 10" barrel 5.56mm AR-15 style rifle with a 6" suppressor on it, and a 16" barrel 5.56mm AR-15 style rifle?

I'd always heard that barrel length (and therefore increased velocity?) was the important factor in AR-15 accuracy, but then gone on to have that debunked. . I.E. "they say",  don't get a 10.5" barrel and expect it to shoot as far, as accurately as a 16" barrel on the same weapon. Is this true? 

Can a suppressor replace some barrel length when going shorter? Is it the velocity that matters most? Does the suppressor's increased velocity (I think) take the place of a couple inches of barrel, or is it not enough?



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Original Post

I can't answer your question regarding the effect of the suppressor, but I can talk to the other issues.  If the barrel wall thickness is the same, a 10" barrel will be stiffer than a 16" barrel, and is theoretically capable of greater accuracy.  I say theoretical because there are other factors.

Twist rate relative to barrel length is also an issue.  In 5.56mm, the twist rate should be faster than the barrel length, i.e. the bullet will complete at least one complete revolution before leaving the muzzle.  If I'm wrong, someone else will correct, but the bullet should be stabilized.

Velocity can have an effect on accuracy, but not at closer ranges.  Twist rate and ballistic coefficient are factors in the bullet's stability.  If the bullet doesn't have the right spin relative to the velocity, it can wobble and lose accuracy.  When the bullet transitions from supersonic to subsonic, your accuracy can go to hell.  So the higher velocity of the 16" barrel means the bullet travels further before it goes transonic.  So yes, it will probably be more accurate at longer ranges where the transonic issues affect the shorter barrel.

Accuracy with iron sights is largely dependent on sight radius, the distance between the front and rear sights.  So if your barrel is longer, and the front sight is at the end of the barrel and you have a longer sight radius, you'll potentially have better accuracy.  But that doesn't apply to optics.

As Dorsai mentioned, barrel length is especially important to squeeze the maximize amount of velocity out of a cartridge.  That is why you see so many Palma and F Class shooters with 30" barrels on their bolt guns.  With the right cartridge components (especially low drag bullets) in a .308 you can stay supersonic pretty much out to 1000 yards.  Going transonic is indeed detrimental to long range accuracy.

My understanding is that a suppressor may add a few extra FPS to velocity but it is not as efficient as a barrel because the purpose of a suppressor is to dissipate (and cool) hot propellant gases in a larger volume container than the barrel itself.

Lately, my fertile mind has been giving thought to a 16" midlength 5.56mm barrel with an over the barrel (OTB) suppressor.  Specifically I have been looking at this 5.56mm AR Performance barrel   with 5/8-24 muzzle threads combined with a .30 caliber AMTAC CQBm suppressor  and everything tucked into a 15" Aero Precision Enhanced or Quantum M-lok handguard

If the specs are accurate, the end result would be a 19.7" long barrel/suppressor combo protected by a 15" handguard with what should be reasonable weight and balance.  Hanging a Magpul UBR stock on the lower might help with the balance as well.

Suppression may be a couple of decibels louder with a 7.62mm caliber can vs. a 5.56mm can but I like the idea of using the beefier 5/8-24 threads and I'm not necessarily looking for the fabled "whisper quiet" suppressor.  I also like the modular design and baffle stack of the AMTAC suppressor and the ability to tear it apart for cleaning and/or repair.

With 77 grain Mk262 ammo such a combination might provide adequate mid-range effectiveness, with sound suppression and all in a decent sized package.

The use of the 7.62mm can also allows you to do a similar setup with a 10" pistol system .300 Blackout barrel or a rifle length gas system 20" 6.5mm Grendel barrel.  Three different calibers (5.56mm, 300 Blackout and 6.5mm Grendel).....all with one suppressor.

I welcome any feedback on this concept that I think addresses some of the OP's "thread hijack" intended. I suspect that building this project will be one of my New Year's Resolutions  although I'm not sure my wife will think it is a worthy goal.


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I've found in the following examples:

 HK 416 10.4" vs 14.5" (77gr BH/mk262)
Match 14.5" Noveske vs 18.5" Douglas (77gr BH/mk262)
AI 308 20" vs 24" medium palma (175gr BH)

That barrel length had no bearing on group sizes at 100y.  While I believe Dorsai is technically correct in regard to mechanical rigidity, I don't feel there is a perceptible difference to the shooter.  I do believe there is regarding muzzle velocity.

Regarding speed and accuracy, this is the hierarchy,I follow for accuracy at distance:

1) High BC at high velocity is king.  RULE: push the best bullet as fast as you can

2) Better to sacrifice speed than BC

This is why I find defining "accuracy" complicated.  I could show you 100y groups from 185gr Juggernauts out of an AI AX and most (myself included) would say are terrible (well over MOA).  However, I can print the same group at 250y where it's under 1/2 MOA and maintain similar sub-MOA standard out to 1000.   Meanwhile, 155gr Scenars out of the same gun are printing 3/8 MOA at 100y but start to suck at about 600 despite their fair BC and higher MV.   Which is the "more accurate" round?

Speed and aerodynamics (BC) are what help a shooter combat the "great equalizer"...wind...more efficiently. If a person only shoots at known distance, and does not shoot in windy conditions, it's all plug and play from their ballistic app (provided they input the data correctly) and a 10" barrel doesn't lose much to 16" at a few hundred yards then.  Unfortunately higher BC usually means longer, which means heavier, which means slower muzzle velocity so it's all a compromise.  So when push comes to shove, and I'm sacrificing a little wiggle room on my UKD targets or wind call for the shorter barrel, I hope I'm exploiting the maneuverability I bought for that sacrifice.  

Well below the point at which a bullet goes trans-sonic, you have to consider the expansion threshold as well or the point at which your bullet is doing its intended ballistic duty or just poking a hole, that's information I would like to know if my MV is 2350fps and my threshold is 1900fps.  

I don't have a ton of time on suppressors, but from the numbers, they are like adding 1 or at most 2 inches (1-2%)back to the barrel depending on can design and what is being suppressed.  So to answer your question, I don't think a 10" with 6" can would stack up to a 16" equally.  I would say, you could make a better argument that a suppressed 12.5" would run alongside an unsuppressed 14.5" M4

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pointblank4445 posted:


Regarding speed and accuracy, this is the hierarchy,I follow for accuracy at distance:

1) High BC at high velocity is king.  RULE: push the best bullet as fast as you can

2) Better to sacrifice speed than BC

Speed and aerodynamics (BC) are what help a shooter combat the "great equalizer"...wind...more efficiently. If a person only shoots at known distance, and does not shoot in windy conditions, it's all plug and play from their ballistic app (provided they input the data correctly) and a 10" barrel doesn't lose much to 16" at a few hundred yards then.  Unfortunately higher BC usually means longer, which means heavier, which means slower muzzle velocity so it's all a compromise.  So when push comes to shove, and I'm sacrificing a little wiggle room on my UKD targets or wind call for the shorter barrel, I hope I'm exploiting the maneuverability I bought for that sacrifice.  


BC is indeed king and when combined with high velocity does help enormously in combating the effects of wind and reduces the bullet's drop over its trajectory.  Take a look at the extraordinarily high ballistic coefficients of these Berger target bullets:        

6mm and 6.5mm bullets rule the long range game these days and with good reason.  They fly farther, buck wind better and drop less than the traditional 30 calibers of old (30-06, .308).  6.5mm Creedmoor offerings are found in many bolt action offerings precisely because of that.

Also, Ruger just started offering their popular Ruger Precision Rifle in 6mm Creedmoor in addition to 6.5mm Creedmoor.  Combine that with this survey of what top precision riflemen use in competition and you'll understand why BC and velocity is indeed important and why 6mm and 6.5mm seem to be the sweet spot in the non-magnum categories.

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Also why we're seeing a lot of love for the 300NM over 338LM in comparing the 230gr .30 vs a 250gr .338

From what I see on Sniper's Hide (which is largely occupied by PRS types), the 6mm vs 6.5mm is split right down the middle.  The high BC 6mm's like the DTAC's and what not have the advantage of speed, but at the sacrifice of barrel life and spotting hits at distance.  Meanwhile, the 6.5mm gives a bit more barrel life and downrange impact.  It's no secret why the 308 is dead in that arena...unless one can afford those bronze flatline bullets.

The MV + BC equation is not hard to figure out, but people can over think it when they are comparing bullets in the same loading.  I won't run anything less than 175gr on any of my 308's regardless of barrel length; often it's still 185gr Bergers.  It did me no good to try and "buy back" velocity with lighter bullets.  Same goes in terms of chamberings for shorter barrels.  The masses say you have to go 308 because it's not velocity dependent and shooting a 6.5mm out of a 16.5", 18.5", or 20" gun is a isn't. 

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To the OP's original question, to rephrase; does a can increase velocity enough to make up for velocity lost by a shorter barrel? The answer is not, not at all, not by a long shot.

Emprically, I have not tested a combination where there has been any statistically significant increase in velocity with a can period. Note how I stated that.

The benefits of a can do not include important or balistically significant increases in velocity.

Lots to digest and thanks for all the replies!

The reason I was asking this was because it's about time to replace my work barrel (going to do the whole upper, for fun).

Currently it's a 12.5" BCM upper/barrel. I use the SilencerCo Saker 7.62 with a 5.56mm end cap on it. I'm contemplating replacing it with a 10.3" BA Hanson performance barrel/Aero Precision upper. I've found, like many told me I would, that once you shoot suppressed you almost never shoot unsuppressed. So I like the idea of a little shorter overall length, since the 12.5"/Saker 7.62 combo does make it sorta longish.

Overgas issues aside (I'm hoping to not have to deal too much with them), I had been thinking about whether or not I'd lose effective range going from the 12.5" to the 10.3", and whether or not the suppressor would mitigate those issues (question, answered, thanks!). 

Previously I'd considered 11.5" as the minimum length for a good balance of reliability/shortness... am I wrong to consider the 10.3" with suppressor for duty/life-safety use? 


     I need to get you through an Armorer Course, as we cover this extensively.  I will try to put some of it here in print.  

There are basically 3 types of ballistics that you you need to consider as it pertains to the AR15 / M16 weapons system: Internal, External, and Terminal.  Internal is what happens inside of the firearm.  External is what happens after the bullet leaves the firearm, before it hits its intended target.  Terminal is what happens after it hits its intended target.    

Internal:  What you need here is ammunition that fits, fires, and can reliably function the firearm.   The ammunition much feed into the chamber, and allow the action to lock into battery.  As it pertains to the feeding cycle, the cartridge must reliably strip off of the magazine and go up the feed ramps.  Once it goes up the feed ramps, it must be able to reliably chamber and allow the action to lock into battery.  So in order to do this the shape and length of the bullet, overall length of cartridge, depth of seating of the bullet, must reliably fit into a magazine, strip off the magazine and have the correct angle as it goes up the feed ramps, fit into the chamber, mate correctly with the throat / lead / freebore so the bolt can reliably lock into battery with the barrel extension. 

Then once the round of ammunition is fired, the gas pressure inside the cartridge must create enough gas pressure to push the bullet down the barrel, and as the bullet passes by the gas port the gas pressure goes through the gas port, and there must be enough gas pressure created to reliably cycle the action rearward so the bolt carrier assembly unlocks, extracts the empty cartridge, and that the bolt carrier assembly travels rearward enough to eject  the empty cartridge, and the hammer gets recocked, that the action spring gets compressed enough to create enough pressure so the bolt carrier assembly can start the feeding / chambering / locking cycle all over again.

External:  The bullet needs to leave the end of the barrel and stabilize, so it can shoot the desired group at whatever distance you need it to.  The external ballistics also have to work in harmony with internal ballistics.  The bullet weight and shape, along with the velocity the bullet is traveling, has to be in harmony with what's going on inside the barrel.   Many people just go by bullet weight and match it to the twist rate of the barrel, which is a good place to start imho.  If you shoot a lot of different loads, you will find that some bullets in the same  weight will shoot tighter groups, and some won't, this can a lot of times be attributed to the velocity of the cartridge, aerodynamic correctness of the bullet shape, but can also be attribute to the bullet shape of how much of that bullet actually makes contact with the the actual barrel rifling.  There are other variables of some of these (but not limited to): barrel crown, free bore, chamber machining, rifling machining, barrel finish, deformation of the bullet as it passes down, erosion, bullet velocity, etc.

Terminal:  This is what happens when the bullet hits its intended target.  If you are shooting paper or steel targets its one thing, if you are shooting to create trauma it is another thing.  From my mind of the Law Enforcement perspective, we want the bullet to create trauma (air in, and blood out).    This is where the opinions based on actual facts from Ballistic Professionals people like Dr Roberts, Martin Fackler as to what specific loads and bullets do and don't do should be taken into account.  Along with considerations given to what the bullet and ammuntion manufacturers develop for ammunition (I am lucky to have a great one close by, that I can get opinions on).  

Terminal ballistics of creating trauma is based on many variables like bullet shape, design, materials, stabilization, velocity, etc.  In the case of the .223/5.56, the bullet has to be moving fast enough to create the desired trauma you want.   Many of the .223/5.56 load development has been done based on 20" barrels due to the history of the AR15 / M16 weapons system.  Those loads were developed to be reliable for internal, external, and the terminal ballistics that the AR15 / M16 weapons system needed.  Now we take into account that many of us in Law Enforcement are using shorter barreled rifles like the M4 in 14.5"-16", and shorter barrels of 10"-11.5",  and we shoot many of the same loads that were designed for 20" barrels, and what we see is that the bullets are moving slower in velocity due to the shorter barrel length.  In generic terms, the shorter the barrel, the less velocity of the load.  This slower velocity will generally cause a bullet to penetrate further (Look at Ballistic Gel Tests).  This further penetration can also result in less trauma.  Now take into account that most of the duty loads that we use in Law Enforcement are a hollow point of soft point of some sort, and these are generally .223 and not 5.56.  The .223 loads are generally developed with less gas pressure, as compared to 5.56 which is higher pressure.   To compensate for the short barreled rifle issues, some manufacturers are now offering special short barreled loads (Federal, Speer, Winchester,  etc).  

Now to put the whole picture together.  You probably won't see a huge difference in accuracy between a short barrel vs long barrel.  What you will find is that the shorter barreled rifles will lose terminal ballistic performance  at longer distances, where the longer barreled rifles will allow better terminal performance at longer distances due to the higher velocity on the bullet.   Do we see a gain in velocity when a suppressor is added, in simple answer yes, it's minimal, and we don't really see any change in external or terminal performance.  

Where we do occasionally see a difference on accuracy is barrel harmonics of adding a suppressor.  A barrel has a harmonic vibration when you fire a round, kind of acting like a tuning fork.  Sometimes when a suppressor is added you might see where the groups open up for accuracy, sometimes groups tighten up, sometimes there is no real change, and sometimes the grouping is similar but there is a definite zeroing shift (We see this often on lightweight barrels).  

Where the issue of short barrels vs longer, suppressed versus non-suppressed on traditional baffle suppressors, is what is the timing of the rifle of getting it to run reliably.  When using baffle type suppressors, the barrel/chamber pressure stays higher longer, resulting in the fired casing staying swelled longer, so you will most likely need to slow the bolt carrier from unlocking a fraction of a second longer (Done with heavier buffers, stiffer springs, regulating gas, etc), so the empty casing unswells and can be reliably extracted.  

IMHO: If going to be using the rifle suppressed and unsuppressed, and lives depend upon it, then don't go under 11.5" for reliability of cycling, and get a short barreled load.  The hot and cold weather, altitude, and .223/5.56 all have effects on how the rifle runs, and how the ammunition performs (internally, externally, and terminally).

I could go on longer, but it's hard to put into written format without sounding like I'm going in circles.   And if I sound like I'm talking in circles, then ask and I will help clarify my explanations.

Hope this helps some.                                        


Greg Sullivan "Sully"
SLR15 Rifles
(763) 712-0123  

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I have an AR with a 10.5" barrel that will easily make hits on steel out to 300 yards unsuppressed with Federal XM193. It will hold between 2-3 MOA at 200 yards depending on ammo type. I recently installed an Omega suppressor using a direct thread end cap and a 22 caliber flat cap. I haven't shot it past 50 yards yet, due to being limited to the indoor range because of the winter season. Accuracy seems to be still holding but I did note a change in POI. An SLR adjustable gas block is used to regulate gas flow. I don't notice any gas to face. I'm quite satisfied with the combination so far.

A poster on another site said they see a difference in performance between the 10.5" and the 11.5" barrel. He said the 10.5" barrel struggles to reach 500 yard targets whereas the 11.5" barrel does fine because of its extra velocity

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I ended up with a 10.3" Ballistic Advantage Hanson barrel from their "performance" series, it actually arrived yesterday in a strange universe-syncing to this thread being bumped. It actually comes with a 1 MOA guarantee for a 5 shot hand loaded or 3 shot magazine fed group at 100 yards with match ammo...  pretty ballsy and comforting if you ask me.


As an aside, I was test fitting the barrel into the BCM cosmetic blem upper I've had sitting around, and I experienced the first issue I've ever had with BCM or the 10 or so cosmetic blem uppers I've dealt with. This one is marked BCM4 on the front just above the gas tube hole. The barrel was a TIGHT fit, to the point I basically had to tap it in with a block/hammer. Measuring with calipers, the interior diameter of the upper was 2 hundreths or so smaller than the barrel extension. It didn't take so much force that I was worried about it, but was something I haven't seen with those uppers before. I don't think the barrel extension was the problem, it measured a nice exact round number in diameter (can't remember but the caliper was directly on 0, I didn't care about what it was just the difference. 

I might be mistaken but I thought that was a design feature of BCM, similar to the "thermo fit" jp advertises on their rifles. Supposedly results in better accuracy.


Someone asked about shooting suppressed all the time if you have the choice.. if you are going to be at the range shooting hundreds of rounds in a session, sometimes it's a pain in the ass to stay suppressed the whole day. You'll be burning off your lube, melting random shit, cleaning more etc.... I personally don't leave it on all day. 

Not to be a killjoy, but I have owned and run every thing from 10.3" to 20" within the M16 FOW. Both quietly and obnoxiously.

The bulk of my time has been on 12.5 and 11.5" guns. I find the 10.3/5" guns to give up too much in terminal ballistics and run too close to the ragged edge of reliability for a duty gun- especially when factoring in suppressed use.

I tend to agree with Paul Buffoni that the 11.5" is the shortest practical barrel length for all around professional use. My experience drove us to 11.5" entry guns. The brass at the time wanted 10.5" because they were shorter, but I could not guarantee function, particularly when the agency jumps from one load to another depending on bid price. That extra inch made no significant difference in handling but a world of difference in reliability and forgiveness.

The only way I would reconsider the 10.3 is if I was a large agency that had a stable, monogamous, long-term ammunition supply, sharp armorers, and permanent thread mount cans. I would also predicate this on a mission set that rarley exceeded 50m and did not exceed 100m engagements. Or if I was also issuing .300 BLK.

I really like the 12.5". Wes Grant was not kidding when he told me years ago that the 12.5" is "Pure Fucking Magic".

It is... and my MSTN built 12.5" has been a workhorse. Suppressed or not, it checks all the boxes for me in a duty gun.

The 12.5" with an OTB Surefire suppressor is still shorter than a 16" barrel or a 10.x" w/ 6" can attached... It has noticably better internal and terminal ballistics than the 10.x" and is quieter than the 16" carbine.

I have 10.3, 10.5, access to numerous 11.5s and have tested for velocity with them, 14.5, 16, and 18.

Ran a suppressed 14.5 with a full size can for a duty gun for some times and absolutely hated the length and weight, so I went to 10.3 and 10.5.  Much, much better.

I've noticed no difference in accuracy between the barrel lengths listed above (except the 18, which is a Noveske stainless barrel and it is sub moa), but then I'm not running magnified optics, match ammo, shooting past 200 yds, etc.  The ones with Noveske CL barrels run about 1.25 moa with 55 FMJ, and the Colt barrels run about 2 moa. 

The 10.3, 10.5, 14.5, and 16 I run unsuppressed and suppressed.

I have not found that suppressed adds more than about 10 fps (AAC 556SD, AAC 762SDN6). 

The 10.x barrels have very little POI shift between suppressed and unsuppressed.   The 16" barrel (Colt 6920) has 3" vertical and 1" horiz POI shift at 50 yds.

For an agency SBR, I would go with 11.5.   They are more forgiving in every way than 10.x.  Ours have been flawless (Colt 6933's).  We have equipped one of them with a GT Halo, also runs flawless.

Since I know how my guns run and are maintained, I feel OK with 10.x for *ME*, and I've been very satisfied with them, suppressed, and unsuppressed.  

Given a choice, I would shoot suppressed all the time, and I mostly do nowadays. 

A 10" HG can be used on a 11.5, and that extra inch of rail may be important to you.  I run 9" rails on my 10.x barrels. 

In the 10.x guns, I run a Gemtech SBC, H2 buffer (I tested with H1, H2, H3), and mil spec standard carbine buffer spring, with FA bolt carrier, and by using the GT SBC, I can switch between suppressed and unsuppressed very easily.   I'm going on 2 yrs on these guns and they have been flawless.

But, I would agree with the others above that 11.5 is better all around and that extra inch isn't likely to be noticed. 

Despite being satisfied with my current guns, I've been contemplating my next SBR to have a 11.5 barrel with a small GP for full time suppressed use, and a GT Trek-T mounted on it semi-permanently. 

We built half a dozen or so 10.5" carbines that I sold to civilian clients, and they have been pretty happy with them. They were built with stripped Stag lowers and DD lower parts kits and the uppers are built from LMT parts.

One of the local PDs came to us wanting some, but I recommended 11.5" barrels for them, as they were for their ERT guys. They basically ended up with modified Colt 6933s. They have been happy enough with them, that they have come back twice more for extra guns.

We are corrently working on a project using RRA pistol lower receivers that we have thoroughly checked and rebuilt with DD, Norgon, BAD, LMT and Geissele parts, and added Law Tactical folders to.

We are just contemplating what barrels to go with. We had initially considered going with 10.3/10.5", but I am leaning more towards 11.5/12.5" right now. These could be purchased by both .mil contractors and LE, in addition to our civilian clients.

We are also looking at .300BLK with 9" barrels as an option. The idea was to give them as small a package as possible, but reliability is our first priority.



Thanks for all the input and advice, I'm in agreement with most of you. Engagement distance isn't a *HUGE* thing for me, although I'm a firm believer in Anything Can Happen, I can only shoot as far as I can PID a threat, which isn't MUCH past 100 yards, even during the daytime, and I'm using a T-2 for sights. If the threat is that obvious at that distance, welp I'll start doing Accuracy by Volume or come up with a different solution, like maneuver. 

I agree as well that 11.5" should be the minimum for agency rifles. This one is mine, I'm comfortable with its maintenance and checking it out with our duty ammo for reliability before I put it into service. 

I decided on the 10.3" because the 12.5" was too long and heavy for me with the full size suppressor.  Then I got thinking, if I'm spending the money again to go shorter, I want it SHORTER not just a little shorter. If that makes sense. 

Longeye, why such a short distance limit (speaking terminal ballistics-wise I assume, not the PID issue I referenced above?) I had originally posed this question because I was nervous about being too range limited, but it didn't seem that was the case? And Ballistic Advantage's "MOA guarantee" sort of put my mind at ease that it would at least be acceptably accurate at 100 with duty ammo. 



Accuracy is not the problem. Any common length barrel is going to be acceptably accurate within the context of a duty SBR, and at any reasonable distance.

I use 100 m as the outer limit for 10.x barrels because that is the approximate distance that I observe impact energy drop significantly when compared with 12.5 and 14.5 barrels.

Some of this field observation, some is a look at model potentiality.

If we say that 1900 fps is the fragmentation threshold, and the 10.X starts at 2300, the 12.5 at 2600, and the 14.5 at 2900 we have a starting point.

The 10 can lose 400fps, the 12 can lose 700, and the 14 has 1000 fps to burn off. That translates to distance and barrier defeat.

The 10 will be struggling to do what the 12 & 14 are loading to achieve at 100, the 12 starts lagging past 200 and the 14 is good to around 300+.

I also take into consideration light intermediate barriers. Bullet construction aside, it takes a certain amount of velocity (conserved energy) to push through barriers and have enough to reserve energy to defeat bone and vital tissue.

If a bullet has used up 400fps defeating a barrier, out of the 10 it is now at the fragmentation threshold, meaning the bullet is only punching holes and not damaging tissue beyond its diameter via expansion and fragmentation. The 11,12 & 14 have plenty of V left to work within this scenario.

The threat may stop or expire due to blood loss, but that moment may be long in coming, relative to dynamic tissue distruction caused by expansion, temporary and permanent cavity, and secondary channels that a few hundred more fps provides.

I realize the MK18 program has been successful for its intended audience, but for me, the 10.5 (suppressed or unsuppressed) gives up more in terminal effect and temperament than I gain in handling.

The other element is over gassing with a suppressor. With my N4 10.3" and a AAC M4-2000 can and HSM ball ammo, the gun started getting sluggish at three magazines and became a bolt action by 120 rounds. Lube would gain another 20-30 rounds.

With the same can on my Noveske 12.5" Crusader, I could go well over 300 rounds before seeing signs of the action slowing. The difference was in how much gas was getting returned to the action.

Ninety+ round engagement is not the norm in the US, but it happens often enough that I want my carbine to be cable of the task with no caveats.


Good comments.

Do you happen to know what  velocity threshold is required to cause expansion of your bonded loads?

What make of 10.5 and suppressor? I assume the AAC 5.56SD and ???

I included the specifics in my post because I suspect that the differences are important. Not all 10.x barrels are ported the same, and not all suppressors produce excess gas blow back. It is certainly possible that the GemTec SBC would have made my Noveske N4 10.3" work much better with the AAC M4-2000. This was before the SBC was a thing though.


An aside:

I will note that adding a suppressor is a very good reason to go shorter on barrel length. And trying to achieve similar overall length as a conventional 16" barrel with the SBR /suppressor combo is solid concept that I embrace.

Back in the Rob_S era, there was a theory that putting a can on a SBR was dumb because it made the combo the same length as a 16". 

But that is not nearly as dumb as putting a suppressor on a 16" barrel, and ending up at 22" overall, or running a 10.x or 11.5" naked and triggering a flashbang at the muzzle on every single shot.

A suppressed SBR offers the best of several things. It is all a compromise.

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Not sure about that.  A very good question, though.  I will have to check on that.

Using a 556SD and Noveske 10.5 CHF. 

I wonder how suppressed Mk 18s are faring in mil use (I got out long before they were even a thing), as to how long they will run before fouling will cause stoppages (certainly not before one expends their basic load).

  That's also one of the questions I have about the USMC experiment in suppressing nearly all the weapons in a infantry BN.

Longeye posted:


The other element is over gassing with a suppressor. With my N4 10.3" and a AAC M4-2000 can and HSM ball ammo, the gun started getting sluggish at three magazines and became a bolt action by 120 rounds. Lube would gain another 20-30 rounds.

With the same can on my Noveske 12.5" Crusader, I could go well over 300 rounds before seeing signs of the action slowing. The difference was in how much gas was getting returned to the action.


That's pretty surprising- I've run 800-900 rounds through my  suppressed SBR over a weekend without recleaning and only minimal re-lubing. That also includes some pretty high volume fire.  It's an 11.5 BCM (A5 buffer and Gemtech SBC) w/ SF SOCOM.

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Finally got around to looking at info on the 55 GD (Speer Product 24446).

Am currently waiting on a call back from Speer's LE rep to ask specific questions about use in shorter barrels.

While I'm waiting, I found some info on Speer's website here:  http://le DOT

Quote, "Gold Dot rifle bullets are optimized to ensure expansion out of barrels down to 10" at a wide variety of velocities out to 200 yards"

Their gelatin shots were may not have been using  a 24" test barrel bc the velocities for their gel shots were just over 3000 fps, whereas the their state the 24" test barrel had a velocity of 3220 fps.


I haven't done as much looking into this as some, but what I did led me to build my 5.56 SBR as a 12.5."

It seems to be the sweet spot of overall length, weight, and ballistic capability.  I am running a SiCo Saker 5.56K w/ direct thread (well, I will be when it clears NFA jail and/or HPA passes), and OAL is just over 16" for a hearing safe 5.56.  I'm sure it would not be a pleasure to touch off indoors, but it's far better than it would be...

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Quick update: even with an H3 buffer, this 10.3" barrel may be a no-go for me with the 7.62 Saker, I do not like it ejecting forward/casings seemingly dribbling out of the chamber. Do not like it one bit.

I don't know what the general consensus is, (well, maybe I think I do) but I don't especially want to start tinkering with things like action springs and adjustable gas blocks. I think I may have to eat the cost of this or try to sell it, and buy the 11.5" I should've in the first place.  

LobsterClaw207 posted:

Quick update: even with an H3 buffer, this 10.3" barrel may be a no-go for me with the 7.62 Saker, I do not like it ejecting forward/casings seemingly dribbling out of the chamber. Do not like it one bit.

I don't know what the general consensus is, (well, maybe I think I do) but I don't especially want to start tinkering with things like action springs and adjustable gas blocks. I think I may have to eat the cost of this or try to sell it, and buy the 11.5" I should've in the first place.  

IMHO there's too much emphasis into what direction the empty casing is ejecting, and try to relate the direction of the ejecting empty casing to the gun being over or under gassed.  The main question is, is the empty casing ejecting?  There are many things that can effect the direction the empty casing ejecting, first the tension of the ejection system, the tension and machining tolerances of the extractor, the speed that the bolt carrier is traveling rearward, buffering system,  which as this relates, the type of casing itself (there is a huge difference between steel and brass), pressure of the ammunition being fired as you will see a big difference between .223 & 5.56, one load versus another (Hot Israeli 5.56 versus LC 5.56, etc).

If the empty casing is barely dribbling out, then your rifle is possibly running too slow.  Try a lighter buffer or lighter buffer spring if running anything in extra power, and see what results you get.  If running an adjustable gas block, then try opening up the gas a little.  I am not a huge fan of adjustable gas on a duty rifle, as many of the adjustable gas blocks have little set screws that can come out of adjustment from shooting and riding around in vehicles.

Greg Sullivan "Sully"
SLR15 Rifles
(763) 712-0123 

Sully, without the Saker on it this rifle was ejecting brass in what I consider a "normal" way, in the context of my experience. The empty casings were flying to 4-5 oclock, about 6 feet or so. Once I put the Saker on, the casings started flying anywhere from 3 oclock to 1 oclock, between 5 feet and 1 foot. All the ammo was American Eagle 62 grain ball, brass cased. 


I also am hesitant to bastardize this further with an adjustable gas block. It is a duty rifle, so I'm sort of weighing my options for now. 

Claw, your carbine is over gassed with the suppressor. It's possible that the carrier speed is enough to over work your extractor spring and even the ejector spring. Replacing the extractor spring should give you more consistent ejection.

The real problem is over gassing. Installing a heavier buffer and a stiffer spring might help, but the real solution is to reduce gas flow

LC -

You changed 1 variable (added the can) and you are getting a different result.

What you are describing is normal, and to be expected, when you put a can on a gun.  A can severely overgasses the gun. 

The very same or highly similar result will occur with an 11.5. 

I've know this because I've tested H1, H2, H3 buffers with several different types of ammo on a Colt 6933 (11.5) w/ and w/o a GT Halo.

Also have tested those buffers and ammo types with 10.3 and 10.5 barrels, with a 5.56 can and a 7.62 can.

You can compensate for this by building the gun with a small GP so it runs correctly  suppressed (but it won't run unsuppressed), or by using something to adjust the gas if you want it to run suppressed and unsuppressed.  You are asking a lot of the gun to have it do two very different things, so you need something to optimize the gun for those two very different things. 

I'm leaving discussion of the variable of the buffer alone for this moment but you can of course change that variable as well, however, adjusting gas flow has a much more significant effect than buffer weight.

I do not prefer AGBs but I have a Noveske SB and 2 GT SBC's. 

A GT Suppressed Bolt Carrier is a very viable solution.  It has been in my case.  I was running a H2 buffer but have gone to a H3.  I use the standard carbine spring.  Ejection is 3:00 to 3:30 using .223 pressure ammunition. 

Watch this video from Aaron Cowan

https://www DOT



My experience is running suppressed 11.5 and 12.5 Colt 633 Commandos and 14.5 M4s with Bell and OPSINC suppressors.  We shot lots of 55 grain A1 Ball, Remington 55 soft points, Federal 69s, A2 Green Tip Ball, and 77s.

The common theme across (for me) was they all tend to make a gas-operated gun filthy.  I suppose the HK416 was supposed to fix that -- I don't know.

The can was for indoors use.  Getting into a structure, then fighting out we needed a weapon effective out to at least 200-300 Meters.  No problem.  After that you need to have good position and form, good optics, or both.

A short-barreled 5.56 carbine beats an MP5SD for fighting once the first loud round, breaching charge, or flash-bang goes off -- then you're not hiding anything.  You can hear better, but if you're in an extended pie fight I don't want my own weapon to be so filthy I start worrying about stoppages.  Five magazines made a thick pudding-like sludge.  Still a great tool for a spotter on a sniper-observer team.

The first end baffle strike and destroyed can I saw (and my battle buddy experienced) was from a 10.5 and a fat Bell suppressor.  After the end cap blew out the baffle stack launched.

My memory is foggy but the 10.5 was never dependable while the 11.5 and 12.5s ran pretty well.

Last edited by Community Member

Tiny sample size, and my notes with exact details have since been lost:

noonish on a hot Ft Benning summer day ~2007  


1 MK 18

1 M4A1

M855 ball

sample size was a 5 shot string with each gun, done with the speed you would use shooting groups to zero with

approximately 10 minutes between strings

chrono placed 10m downrange

The Mk 18 gave up approximately 300 fps to the M4, and gained back approximately 45 fps with the  suppressor. 

Group sizes were comparable at 25m, which means approximately nothing. 

At up to 300m, with issued ammo, I have found the 10.x” guns (HK or Colt) to be as accurate as the 14.5” guns. 

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