5.56 10.5" barrel thoughts for LE work?

[Galbraith]

I'm currently splitting the duties of firearms instructor between several other officers, and the one who spear heads equipment procurement is pushing for converting our 40 AR-15s from 16" barrels to 10.5" barrels. I have generally been happy with running 14.5-16 barrels. From the large pool of knowledge in this forum, I was hoping to hear some opinions on this matter. My primary concerns are ensuring good terminal effects of the ammunition out to 200yrds(we are running Speer 62gr Gold Dots). I also have concerns about reliability and muzzle blast(trying to push for suppressors). Any insight into this equipment decision would be most helpful.

[navyman8903]

Not that you can hear a lot with 16" or 14.5" rifles going off, but a 10.5 is going to be even more oppressive. Additionally the ammo concern is valid, you might have to switch to 77gr, but I know of other departments running SBR's with 62gr ammo. You're not going to get the same ballistics out of the gun that you're getting now obviously, and in LE you're going to be dealing with multiple threat scenarios. Which those rounds have to deal with. Range, clothing, body type, armor possibly....you get the idea. I also think suppressors for those SBR's will be a requirement, but I doubt they'll spring for them. My wife's department authorizes SBR's but the cans are taking forever to get "validated."

[TGS]

I'm currently splitting the duties of firearms instructor between several other officers, and the one who spear heads equipment procurement is pushing for converting our 40 AR-15s from 16" barrels to 10.5" barrels. I have generally been happy with running 14.5-16 barrels. From the large pool of knowledge in this forum, I was hoping to hear some opinions on this matter. My primary concerns are ensuring good terminal effects of the ammunition out to 200yrds(we are running Speer 62gr Gold Dots). I also have concerns about reliability and muzzle blast(trying to push for suppressors). Any insight into this equipment decision would be most helpful.

I think 12.5" is going to be your sweet spot.

The blast is noticeably less than 10.5", the service life is longer, and the velocity increase over a 10.5" is exponential within just those few inches. The 10.5" is useful for niche applications and you can make them reliable these days. We use Daniel Defense Mk18s, and they are awesome to shoot as long as you're wearing double ear-pro. The recoil is amazingly soft, and even against "legacy" Mk18s they are very lightweight and handle like a dream. Shooting next to any sort of barrier feels like getting hit in the face. I don't think they're an ideal weapon for a general patrol rifle, and think 12.5" is a much better option.

The 12.5" mitigates the concussion and will extend the service life of the weapon. However, to your primary concern of terminal effects out to 200 yards, the Speer 62gr Gold Dot is good out to ~200 yards from a 10" barrel. It will expand down to 1800fps or so, IIRC.

ETA: @Galbraith,

Where in MO are you located? There's a sergeant at UMKC PD with a sweet 12.5" setup. Gun guy. I'm sure he wouldn't mind talking to you about it or shooting if you reached out to him.

[Mike C]

I'm currently splitting the duties of firearms instructor between several other officers, and the one who spear heads equipment procurement is pushing for converting our 40 AR-15s from 16" barrels to 10.5" barrels. I have generally been happy with running 14.5-16 barrels. From the large pool of knowledge in this forum, I was hoping to hear some opinions on this matter. My primary concerns are ensuring good terminal effects of the ammunition out to 200yrds(we are running Speer 62gr Gold Dots). I also have concerns about reliability and muzzle blast(trying to push for suppressors). Any insight into this equipment decision would be most helpful.

While I am not an expert nor DocGKR I absolutely would not want to run a 10.5" without a suppressor, I say that having shot a lot of 14.5's indoors with and without hear protection while overseas in Iraq. When being in a room with or near AWG and SF folks who where running 10.5's it was deafening. I will leave @DocGKR to speak to effectiveness and what what range terminal effects will be adequate for the ammunition you are seeking info on. I will say that he has stated that the 62gr GD was good stuff better still was the 75gr stuff. If you have credentials I'm certain you can call Speer/ATK and get information that would other wise not be published, outside of that I would PM DocGKR directly. He is certainly the person I would seek out. Here is a good thread on the topic in general with some excellent advice on ammunition selection by the good Doc.

https://pistol-forum.com/showthread....-mm-Duty-Loads

[rob_s]

I'm pretty out of touch with the AR world these days, but I use to know some stuff, and I'm not in LE but...

Oversimplifying:
I would go 12.5" if unsuppressed, and 10.5" if suppressed, and I'd really only go suppressed these days if it was a dedicated gun/upper. I'd still probably use a brake mount just to help protect the baffles (if that's even still a thing) but I'd work on "tuning" the gas port down (probably with an adjustable gas block) to optimize the use of the suppressor just to keep as much of the backsplatter to a minimum as possible. Even with all of that, I'd want a 7.62 can so as to make it do multi-duty (again, good reason for the brake mount).

[voodoo_man]

Completely depends on what your mission and AO is.

If you work in an rural department a 16" might be worth the FPS over a 10.5".

If you work in an urban department a 10.5" might be worth the CQB/vehicle movement ability as engagement distances are likely sub 100m.

As TGS said, 12.5 is probably the best of both worlds, but I'd say most departments don't generally care about the individual needs, they just buy whatever is cheapest.

[HCM]

11.5” and 12.5” DI guns are notably more reliable than 10.5” /10.3”.

In addition to the noise and blast issues already noted, the 10.5” gun wear at an accelerated rate vs longer guns.

[HCM]

I'm pretty out of touch with the AR world these days, but I use to know some stuff, and I'm not in LE but...

Oversimplifying:
I would go 12.5" if unsuppressed, and 10.5" if suppressed, and I'd really only go suppressed these days if it was a dedicated gun/upper. I'd still probably use a brake mount just to help protect the baffles (if that's even still a thing) but I'd work on "tuning" the gas port down (probably with an adjustable gas block) to optimize the use of the suppressor just to keep as much of the backsplatter to a minimum as possible. Even with all of that, I'd want a 7.62 can so as to make it do multi-duty (again, good reason for the brake mount).

I would not put adjustable gas blocks on a duty rifle, especially not an issued duty rifle.

[John Hearne]

In a 5.56 gun, I wouldn't go shorter than 11.5" unsuppressed unless it was an honest-to-god Daniel Defense MK18 upper. BCM was pretty adamant about not going below 11.5" for reliability. IIRC, there was a 40% increase in dwell time when you stayed at 11.5" versus 10.5"

[rob_s]

I would not put adjustable gas blocks on a duty rifle, especially not an issued duty rifle.

Yeah I don’t think I would either. I got a bit carried away with the “suppressed” side when what I want to reinforce is that I’d suggest 12.5 for the OP’s situation.

Of course, that’s assuming that they have to do anything at all. It would not surprise me in the least to discover that the office that wants to make the switch is caught up in just wanting short barrels. Particularly if the current barrels aren’t shot out or otherwise unsat other than length (which is also unlikely).