5.56x45mm- Ballistics & Wounding Statistics - Short Range

[ryan3030]

I'm working on a new AR build and the age old question of 'how long of a barrel do I need' came up. Obviously as long as I can tolerate while keeping the form factor as close to small as I can get. We all understand the correlation of barrel length and powder charge/bullet weight to exit velocity, but it can be hard to find a sweet spot for a specific application without detailed statistics.

It's been awhile since I've seen a comprehensive study on barrel length, load, velocity, and wounding potential. Can you share any that you've seen in recent memory? My 'sweet spot' is going to be 5.56mm on targets within 100m, 200m at most. I'm really trying to keep this build as close to 'PDW" size as possible (discreet, small, light) so studies that include very short barrels are helpful.

Thanks for any help you can provide!

 

[Ggreen]

My 11.5 shooting 556 55gr has zero issues punishing silhouettes at 200yds, and ringing them with authority. At 25yds it's an absolute hammer, and it's very fast and easy to work cover drills. With my Witt machine canooter suppressor it probably footprints 16. I almost refuse to shoot without can anymore, especially on a pdw.

You'll always get better numbers with longer bbls, but you really lose a lot of utility.

It's s the top one, the bottom has a 12.5 wolf t91 upper on it, and it's a gnarly mfer. I like them both a whole lot.

 

[Ggreen]

This site has a quick reference that helps

BBTI - Ballistics by the Inch :: .223 Rifle Results

 

[johntheplinker]

Look up the work of Dr. Gary Roberts and Dr. Martin Fackler.

 

[DadSmith]

10.5" is as short as you want to go. It will still shoot accurately out to 300 yards.

 

[bwframe]

How effective is .223 from a 10.5" barrel at 300 yards? Is there still a large wound channel or are the bullets just passing through at the lower velocity?

 

[EricG]

Look up the work of Dr. Gary Roberts and Dr. Martin Fackler.

This ^



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[Hohn]

You will find that the performance ends up depending much more on the particular load than on the barrel length. There are some loads that lose effectiveness quickly at MV drops. M855 sucks regardless of barrel length. Mk262 works even in 10.5s.

I'd recommend avoiding the "frag" style loads for short barrels; stick with a JSP, monolithic (barnes) or bonded load. The new Gold Dots are excellent from short barrels.

 

[SmileDocHill]

IIRC, Larry Vickers mentioned that in VERY general terms you start getting effectiveness and functional issues shorter than 16". "generally speaking" meaning, individual guns can be build to be very reliable shorter than that but for something like a department or military it is harder to get a ton of them and expect all of them to be reliable. Terminal ballistics start to taper off below 16" barrels also.
Like I said, this is just what I remember my take home message being from what he said. It may not be 100% accurate. I would trust what he said, I just don't 100% trust I remember correctly.

I can say I've seen a fair share of less than 16" barrels result in rounds not penetrating the target backer (friggin cardboard or plastic) at 200, 300, 400 yards at Camp Atterbury on several occasions.

 

[dung]

I would be surprised about it not going through cardboard at those distances. I know mine (18" barrel, XM193) doesn't look/sound like it hits steel very hard at 500, but would think it would at least poke a hole.

 

[cosermann]

Per - https://www.ar15.com/ammo/index.html , the standard M193 and M855 loads drop below their fragmentation velocity (approx. 2700 fps) at roughly the following distances in the following barrel lengths.

Of course, this only applies to these loads. Different bullets, like those designed to expand, change things a bit.

Distance to 2700 fps	20" Barrel	16" Barrel	14.5" Barrel	11.5" Barrel
M193	190-200m	140-150m	95-100m	40-45m
M855	140-150m	90-95m	45-50m	12-15m

 

[pblanc]

The answer probably depends a lot on what type of ammunition you intend to use. It is generally pretty well established that for FMJ 5.56x45 the wounding potential depends to a considerable degree on whether or not the projectile yaws and fragments when it strikes a soft target. The likelihood of that occurring depends on multiple factors including the "angle of attack" (angle at which the projectile strikes the target", "fleet yaw effects" (barrel to barrel variations that influence the likelihood of bullet yaw and fragmentation), depth of tissue penetration, and impact velocity. The "conventional wisdom" is that for 55 grain FMJ ammunition the likelihood of bullet yaw and fragmentation drops off considerably at impact velocities below 2600 fps.

Here is an article from Martin Fackler that is old, but still relevant insofar as FMJ military rifle cartridges are concerned: https://www.ar15.com/ammo/project/Fackler_Articles/wounding_patterns_military_rifles.pdf

The article demonstrates that M193 55 grain FMJ has almost no potential for fragmentation at impact velocities less than 2400 fps, even if tissue penetration depth and angle of attack are favorable. M855 ammunition requires even greater penetration depth for fragmentation. With a 10.5 inch barrel, 55 grain .224 caliber will only achieve a muzzle velocity of around 2750 and heavier projectiles will be slower still. If the muzzle velocity is 2750 fps the projectile velocity will have dropped to 2400 fps or less by 100 meters downrange. At that point, the projectiles will probably only be drilling 22 caliber holes.

Of course, that is for FMJ ammunition. If you are wanting to go with a barrel as short as 10.5" you are probably better off using some type of soft point, expanding ammunition. The question of which is best often comes up. Here is test of multiple different types, most of which were shot with 16" barrel, but the Corbon 53 grain DPX was shot from a 10.5" barrel and performed well in gel tests: https://www.activeresponsetraining....ults-best-choices-for-a-defensive-rifle-round. It is possible that some of the other loads would work well in a shorter barrel, but I would probably contact the manufacturer for suggested minimal impact velocities to guarantee expansion.

Here's a thread on another forum discussing .223 Rem SD ammo choices for short barrels with links to several similar threads: https://www.ar15.com/forums/ar-15/Best-5-56-defensive-round-for-SBR/16-737669/

 

[DadSmith]

How effective is .223 from a 10.5" barrel at 300 yards? Is there still a large wound channel or are the bullets just passing through at the lower velocity?

The 75gr Hornady match with a 10.5" barrel still has 2300 fps at 15 feet from muzzle. At 300 yards according to calculations it slows to around 1680 fps which is around 440 ft lb energy. As to the wound channel I would not know. The a accuracy is still good though.

 

[Tactically Fat]

So what you need, clearly, is a 22" bullpup.