I know alot of places have moved to 556 due to increased terminal effectiveness vs PCCs as well as less overtravel through structures. I was looking at short barrels and wanted some feedback, does 556 travel further through walls from a 8.5-10.5 vs a 14.5-16? I know you lose range for terminal effect when you drop velocity/bbl length but do rounds still break up /not travel as far or are you losing so much velocity that you go back to pistol caliber like punch through objects? Is this a moot point with modern purpose built rounds vs .mil ball?

I hope this is coherent, as a disclaimer, I'm typing this up pre coffee this morning.

Original Post

I'm curious too.  I don't know a whole lot about the magic of ballistics.  When I attended the carbine crse at Gunsite in 97, Bill J. gave an intro which included a study about 5.56 bullets shattering at highest velocity yet, after losing some velocity, punching through brick walls.  He even advanced the theory that, indoors, 9 mm may present more of a penetration problem.  My gun-lovin mind was blown.  It's the first time I recall someone dismissing the sub gun obsession of the 80s and early 90s (born out of the exciting SAS embassy assault). 

Since I was a serving soldier and we no longer had SMGs on issue (as of 88), I hadn't given it much thought.  As he pointed out, "why would you want to spend over a grand for an MP 5 to launch pistol bullets when you can have a rifle about the same size/weight for half the cost?"  First range session he hoisted one of the Colorado SWAT guys' shorty ARs and said, "Remember.  This may be a lousy M14..." (Keep in mind Bill was a Marine VN vet and there was still a love affair going round for the M 14 as a proper 'battle rifle' in the 90s.)  "...but it makes for a bitchin' MP 5!"  

Joined sometime in 2008.                  Live in Canada.        

The study I read is probably over 30 years old now.  I don't recall the barrel lengths used, but the 5.56mm was probably 55gr from a 16" or 20" barrel.  I don't think the barrel length will be an issue for this question however.  What they found was that 5.56mm bullets tended to upset when they entered the drywall and then fragment.  Consequently, there were often fragments on the other side, but not always, and very rarely did a bullet make it through.  5.56mm bullets in FMJ configuration get their lethality by having an early yaw (all pointed rifle bullets will yaw, or tumble because the center of gravity is to the  rear of center.  When the yaw occurs is very relevant to lethality because if it doesn't yaw (overly stable), it makes a small, narrow permanent wound channel through most tissues.  With 5.56mm, if there is enough velocity, when the bullet yaws, the stress on the bullet is too great and it breaks and fragments at the cannelure.  That is why it creates the amount of tissue damage it is famous for, and why it breaks up going through walls.  That threshold is about 2,500fps, so it is easily in excess of that, indoors, from a 10.3" or longer barrel.  

That study was part of the reason we saw "SWAT" teams transitioning from 9mm SMGs to SBRs in 5.56mm.  Less risk of an over penetration that could injure someone on the other side of a wall.

-------------------------

Mark

Swear allegiance to the flag Whatever flag they offer

Never hint at what you really feel

Teach the children quietly For some day sons and daughters

Will rise up and fight while we stood still

 

Joined:  2/24/2003                          Location:  Nevada, USA

Keep in mind that FMJ and Bonded Soft Point are very different bullets that do very different things. Reading a study on 55gr FMJ is not useful if you are using or being issued 64 gr TBBC, Speer Gold Dot, Winchester Ranger or GMX.

At least in vehicle shooting, we are seeing better penetration with BSP than with FMJ, unless it is Green Tip. The FMJ is tending rivet or banana and either deflect badly or hit side on which make it  burn energy it doesn't have to spare.

Yeah I recently did a vehicle engagement class and quite a few of us were surprised finding that some 45 ball rounds wouldnt punch a door but a bunch of bonded 9mm rounds would do it with energy to spare. I'd love to get some ballistic gel in a car and go nuts with some testing. I've done two ballistic workshops but its interesting to add variables like wiring harnesses and speaker frames etc. I suppose the same holds true in a house with wire bundles pipes and door joists etc.  

Dorsai touched on it.    Expansion threshold...

If you are expecting a certain behavior out of a specific projectile, it will have an ideal range of velocity where that is most likely to occur or a point at which it is likely not to occur.

Aside from the schism between those that believe 10.5" or 11.5" or 12.5" is the shortest to go...

Take the TSX barnes bullets; I know the expansion threshold is somewhere down around 1900fps and that is relatively low compared to some that rate 2200-2300fps.   Assuming there is a good 8.5" AR15 (as I've yet to see one) your MV's are going to be dangerously close to the expansion threshold of most decent bullets.  So you now have a questionable system, that's a horrible experience to fire unsuppressed that's takes a lot of juice off of a bullet that thrives on velocity.  Not a 300 BO guy, but this is where you 300 BO. 

I abide by the idea that unless you're issued an HK416 or MK18...go 11.5"+ if you must. 

"Pain, we endure...faulty weaponry, we do not."

Longeye posted:

Keep in mind that FMJ and Bonded Soft Point are very different bullets that do very different things. Reading a study on 55gr FMJ is not useful if you are using or being issued 64 gr TBBC, Speer Gold Dot, Winchester Ranger or GMX.

At least in vehicle shooting, we are seeing better penetration with BSP than with FMJ, unless it is Green Tip. The FMJ is tending rivet or banana and either deflect badly or hit side on which make it  burn energy it doesn't have to spare.

...and FMJ ain't FMJ either.

Lotta difference between Norinco 55gn FMJ & (say) M193

This all started with my thinking about a super shorty for a backpack. I've looked at the B&T APC223, Bren 2 and Sig 553 and all have barrels hovering in the mid 8" range. I agree I'd prefer a longer barrel but then the backpack gets bigger and more 5.11y. Its also far more maneuverable in a tight  space.   This got me thinking about using the shorter barrel and what i'd be giving up going from an 11.5 down to a 8.6ish bbl and what i'd lose for terminal effectiveness and overpenetration concerns. I have plenty of stuff with far more versatile barrels, I'm just seeing if I got too far down the rabbit hole with the barrel length. I'd stay away from ball and go with a round thats more purpose designed but it got the gears turning. 

Thank goodness.  Something like those or a Krink/ACE I get the appeal for concealment.  A 553's not going to suck dick for coke like an 8" PWS I see on the reg.  Those things shoot minute-of-dude (the PWS).  

I just remembered...I don't know if you can get it; RUAG makes a purpose-built shorty .223 cartridge with a HUGE open tip on it.  I may have a round or two around here left over from an accuracy experiment. 

 

"Pain, we endure...faulty weaponry, we do not."

anubismp posted:

Yeah I recently did a vehicle engagement class and quite a few of us were surprised finding that some 45 ball rounds wouldnt punch a door but a bunch of bonded 9mm rounds would do it with energy to spare. I'd love to get some ballistic gel in a car and go nuts with some testing. I've done two ballistic workshops but its interesting to add variables like wiring harnesses and speaker frames etc. I suppose the same holds true in a house with wire bundles pipes and door joists etc.  

This'll sound amateurish on my part.  I enjoy watching Paul Harrel's vids on YT.  He's done a few where he's shot up cars (not in a goofy red neck fun way) but in order to show what does and does not go through.  He also does a vid comparing 5.56 with 7.62 x 39 with door penetration etc.  After 35 years in the army , I never got to shoot a bunch at cars and compare various calibres.  I could never afford to do it privately.  Ergo, I have to watch some guy on YT do it.

Joined sometime in 2008.                  Live in Canada.        

anubismp posted:

This all started with my thinking about a super shorty for a backpack. ///////// This got me thinking about using the shorter barrel and what i'd be giving up going from an 11.5 down to a 8.6ish bbl and what i'd lose for terminal effectiveness and overpenetration concerns. ///////. I'd stay away from ball and go with a round thats more purpose designed but it got the gears turning. 

I am not saying ball/FMJ sucks, just that it does what it does differently than BSP or Poly Tip Expanding like Amax or Vmax. At the lower velocity thresholds, the Vmax type loads start to make some sense. Keep in mind that a BSP that fails (doesn't expand) acts more like an FMJ with or without tumble. The BSP will still penetrate to the vitals. But a Vmax that fails (fragments early and doesn't penetrate) acts like a bad flesh wound. The only way to prevent early fragmentation is driving the Vmax bullet slower and reducing the impact forces that creates the fragmentation. A VSBR tends to do that by virtue of its short barrel. As you can tell, I bias towards penetration and bullet integrity. Given a choice, I would pick BSP, FMJ, then Vmax in that order.

For a backpack gun, I would embrace the half pound penalty of a LAW folding stock adapter and keep my barrel at or above 11.5" in order to reduce OAL while still maintaining performance and reliability.  As Pointblank4445 says, below 11.5" you are quickly getting into 300 BO territory... Or you can just embrace a PCC for that role. Or do the asymmetric thing and buy an NATO AUG, which is the easy button and has no real down side.

Longeye posted:
anubismp posted:

 


For a backpack gun, I would embrace the half pound penalty of a LAW folding stock adapter and keep my barrel at or above 11.5" in order to reduce OAL while still maintaining performance and reliability.  As Pointblank4445 says, below 11.5" you are quickly getting into 300 BO territory... Or you can just embrace a PCC for that role. Or do the asymmetric thing and buy an NATO AUG, which is the easy button and has no real down side.

I was reluctant to mention the LAW folder as I am in no way an authority on anything. I was fascinated by the combo of the LAW coupled with the quick removeable barrel (forget the name) (edit Dolos) that meant you could pack a rifle in an innocuous camera case (as posted elsewhere).  Seemed a good idea to me FWIW.

https://www.lightfighter.net/t...camera-case-worth-it

https://www.youtube.com/watch?v=iHloym2YvwI

 

Joined sometime in 2008.                  Live in Canada.        

As to bonded bullets . . .

. . .  slight difference for 62 grn bonded 11.5 vs. 14.5 through drywall.  Not enough to be concerned about.

Remember, also, that most of these bullets will go through multiple walls (typical North American construction), so to think that x is better because it went through only 4 walls instead of 5 isn't the most important thing. 

 

Add Reply

Likes (1)
David Reeves
Post
Copyright Lightfighter Tactical Forum 2002-2019
×
×
×
×
×