I was having a discussion with a friend regarding the use of short barreled ARs for entry teams. My point was the ability to easily maneuver a shorter barrel in tight spaces for CQB applications, and the 5.56mm is more versatile than the 9mm sub guns. My buddy feels that having a shorter barrel is a disadvantage due to it’s inferior ballistics, and was told by a gunsite instructor that short barreled ARs don’t reliably penetrate body armor. I don’t know what the ballistics are out of a 10.5" barrel, 1:7 twist, with a 55gr 5.56mm, but I don’t think it would make a huge difference in CQB engagements. What do you guys think? Is there any hard data on the subject?
Depends on the body armor. A 10.5 should penetrate any soft panals.
For entry work, the distances you’d be shooting people at are probably fine for a 10.5. I prefer a 11.5 for the additional velocity and dwell time.
At the distances that you describe 55gr, even a hollow point, will reliably penetrate soft armor panels and kevlar helmets. Unfortunately this has been best illustrated in blue on blue incidents operationaly and during training accidents.
Any reports that I can get my hands on? Any public articles on the web regarding these negligent incidences? I’m trying to collect some hard data that will support my argument, not for my ego, but for educational reasons.
I would think that truly detailed instances would be difficult to document, you typically run into things like when Trooper Brinkerhoff was killed here in NY:
http://www.officer.com/web/online/Top-News-Stories/Arizona-SWAT-Member-Hit-by-Friendly-Fire/1$47998
This is the first time I’ve tried to post a link. But if that doesn’t work just google (arizona swat member hit by friendly fire.)
I have attached a bullet velocity chart. This gives a good reference for velocities out of various barrel lengths. The key to the 5.56mm round doing any damage is its ability to fragment. Generally speaking it will not fragment at velocities below 2,700 fps when it hits something. So looking at this chart, you will lose velocity the farther it gets away from the barrel. In a CQB situation, generally you should not ever see anything more than 25 yards. You will also be better off with a 11.5" barrel , because the 10.5" will be borderline. 55 grain ammo would be better with a shorter barrel because it is slightly faster than 62 grain and will fragment better.
As for penetration of body armor, any of these figures would penetrate level IIIA at these ranges.
Here’s some data from a range trip with my LMT 10.5" SBR
Win. 5.56 Q3131 55gr.
90 rounds fired:
Hi Vel: 2959
Low Vel: 2749
Average Vel: 2840
Black Hills 75 Gr. Match HP
25 rounds fired:
Hi Vel: 2405
Low Vel: 2322
Avg Vel: 2362
PMC 55 Gr. FMJBT
20 rounds fired (one box)
Hi Vel: 2554
Low Vel: 2426
Avg Vel: 2514
What is the source of these velocities? I’d like to use this as a reference for a project, but I want to confirm the information imparted.
It is from a Bushmaster comparison test. Here is a link for more details on it.
i was just reading the S.W.A.T. mag. (nov.09), on page 74 they tested troy’s M7A1 7.5" barrel, it pierced the Safariland level III vest at 50 yards. if 7.5" can pierce level III 10.5" should be easily done
I had the same question, when we were spec’ing 10.5" barrels for use on our police department. This is the Information I recieved from Gene Swanson at Lewins Machine and Tool. I hope he doesn’t mind me throwing him out there like this.
“With a 55gr bullet and the 10.5 inch barrel, your looking at about
2600fps at the muzzle. At 100yds it’s roughly 2300fps. The 16 inch
barrel will be around 2800fps at the muzzle and 2500 at 100yds.”
Gene Swanson
Technical Specialist
Lewis Machine & Tool Co.
My team uses select-fire 10.5" 1:9 ARs for entry teams. We shoot Federal LE223T1 55gr JSP rounds and we have always reliably penetrated level IIIA vests and IIIA ballistic shields out to 25 yards in testing. It also performs relatively well with barrier penetration to include auto glass. I can tell you that I had to use my weapon for its intended purpose and it performed as it was supposed to if not better. I don’t like to post it all over the net, but if you need any detailed info, feel free to PM me. I would not trust FMJ to fragment reliably out of the SBR, but the JSP is well suited to this role. The SBR has its place, but you need to make accommodations if you want good ballistics.
EMT370 brings up a good point. In the LE community, there is greater lattitude in the type of ammunition we are allowed to use. Soft point and hollow point rounds are allowed, whereas the military is restricted to FMJ rounds. The type of ammo usedby LE would not be allowed under the Geneva Convention. That greatly effects the lethality of the round and transfer of energy.
If you’re using TAP (or similar) you shouldn’t have a problem.
For CQB I like and 11.5 with 75gr OTM(Hornady TAP bullet). The round will still frag out of an 11.5 at CQB distances.
Would you like to amend that statement? 
-B
If you could enlighten me it would be much appreciated.
As others have stated, the magic 2700fps line applies to military FMJ-type rounds and their ability the destabilize and fragment. It doesn’t apply to rounds like TAP or other types of specialized rounds which readily destabilize and fragment far easier than FMJ rounds. A 10.5 barrel should be fine for CQB work, but not ideal for an all-around carbine. Some of my department’s SWAT members use shorty barrels, but our standard patrol rifles have a 16" barrel.
Holy thread resurrection batman. I grabbed this thread off a google search for “ballistics out of a 10.5”.
Anyhow, the bolded part has me curious. I’m currently done adding any bells and whistles to my rifle, and I’m already bored. So I’m looking at putting a new barrel on it. I’m currently running a 16" carbine length gas system (S&W MP15). I’m curious as to what you all think is the “ideal all around patrol carbine” in terms of barrel length and gas system.