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Caveat.....I've read Doc Roberts post on duty 5.56 loads ad naseum and spent way too much time on google....soooo....

5.56 has all but dried up locally.  And what I can find on the web is fairly expensive.

I recently built a 10.5" AR and in the quest for an appropriate defensive load have found that, based on research,  heavier bullets are better and can pull double duty in my SPR.  The issue is all the data I've found/read/watched on youtube utilizes the 5.56 loads.  I can find 75gr PMC OTM rounds locally for fairly cheap (under 20 bucks a box) but they are 223 and not 5.56

Am I just overthinking this whole thing?  Do I loose a ton of effectiveness by using 223 in lieu of 5.56 in typical sub 200 yard ranges?

Thanks in advance.

Original Post

For max effectiveness, it’s about expansion/fragmentation velocity threshold for the bullet you are firing, the muzzle velocity of that bullet out of your gun, and the distance of the threat. For example, 75 gold dot (a .223 loading) was designed with consideration for SBR’s. 1950 FPS is the expansion threshold for the round per the Speer rep I spoke with.  Out of a 10” barrel, you’ll probably maintain 1950+ to at least 100 yards, but not likely to 200 yards. If you want to go with PMC I’d see if they are loading with the Hornady T1 75 grain BTHP and find out its expansion velocity  and figure what distance you’ll likely achieve that velocity with your short barrel.  

Also, if you want a 5.56 load that performs well out of SBRs (at least at close range) Federal’s 62 grain tac bonded is available online for 1.10 per shot (not sure if that’s within your budget).

Available here: https://www.bonefroggunclub.co...al-bonded-xm556sbct3

 

.223 pressure loads will work well.  OTM rounds may not be the best choice for defensive use. Gold Dots are my personal go to round, LE223T3 and Winchester Ranger 64gr bonded are also good.
Where you will lose more effectiveness is with the 10.5" barrel.
11.5" is a better minimum, and 12.5" is likely the ideal compromise if you are running suppressed and doing work past interior distances.
If you are not running suppressed, I can't think of many reasons to go less than 14.5".

@Community Member posted:

.223 pressure loads will work well.  OTM rounds may not be the best choice for defensive use. Gold Dots are my personal go to round, LE223T3 and Winchester Ranger 64gr bonded are also good.
Where you will lose more effectiveness is with the 10.5" barrel.
11.5" is a better minimum, and 12.5" is likely the ideal compromise if you are running suppressed and doing work past interior distances.
If you are not running suppressed, I can't think of many reasons to go less than 14.5".

With the gold dots are you running the 62gr soft point or 55gr?  

@Community Member posted:

Our duty ammo is Federal LE223T3 62gr .223, for both our patrol 14.5" and swat 10.5" rifles. It's been an excellent performer in both barrel lengths in multiple OIS events.

That's our duty load as well.  I'm guessing I'm trying to reinvent the wheel here and will just stick with one ammo type.  I'm thinking this will work in my SPR as well so I need to stop overthinking this.  

Post Car:

My load is the 62 gr Gold Dot. I use it in my BCM 11.5" patrol rifle, my Noveske 12.5", and my 16" Noveske.

It performs exceptionally well both terminally and when measuring group size in each of those carbines. I have been impressed with its performance on vehicles, auto glass, and "bullet resistant glass" when I had the opportunity to evaluate performance against those barriers across the three barrel lengths.

FMJ, generic 55gr soft point, and green tip generally failed against those barriers, or exhibited significantly diminished performance after defeating the barrier. Barrel length didn't play a large role in the results.

@Community Member posted:

Post Car:

My load is the 62 gr Gold Dot. I use it in my BCM 11.5" patrol rifle, my Noveske 12.5", and my 16" Noveske.

It performs exceptionally well both terminally and when measuring group size in each of those carbines. I have been impressed with its performance on vehicles, auto glass, and "bullet resistant glass" when I had the opportunity to evaluate performance against those barriers across the three barrel lengths.

FMJ, generic 55gr soft point, and green tip generally failed against those barriers, or exhibited significantly diminished performance after defeating the barrier. Barrel length didn't play a large role in the results.

Thanks you for the intel.  It certainly helps with which direction I'm going to go with this setup. 

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