7.5" vs 10.5" barrels for pistol

[HardToHandle]

Like everyone else here, I have a 10.5" SBR and don't have any experience with a 7.5" SBR.

I hope some who have run the 7.5" barrel will chime in here and relay some experience based on actual use.

I had a 7.5 DPMS kitty Kat upper. The first 100 rounds were a little unreliable, with 4-5 FTE and FTF each. Some of those issues were due to be breaking it in the dead of winter - air temperatures in the single digits. After adding a DFender on the extractor spring and running more ammo through reliability became a failure of 1:200 with cheap Wolf and Winchester White Box.

Frankly, I bought the DPMS as a proof of concept - I did not care for what it offered. I traded it off for a small profit and some conclusions.
1) 7.5 ballistics were underwhelming in theory, especially in cheap ammo and 1:9. Ammo options have improved and SOST type cartridges provide a more adequate option in a longer short barrel. I rarely shot beyond 50 yds and noticed no accuracy issues.
2) The 7.5 appears to be wasting much of propellant out of the front end in blast and light. It beats a sharp stick, but the cartridge was not designed for this barrel length.
3) the Kitty Cat had a jackassery of a heavy, thick aluminum fore end... Appreciated for the heat protection, but unnecessary heavy on the front end.
4) the simple mechanics of 7.5 barrel makes accurately holding a pistol with such a short fore end seemed a big compromise. I found the SAS sling method with Magazine well back pressure worked, but the heavy foreend moved the center of gravity too far forward. A longer fore end or lighter foreend would have been more valuable.

That all said, I am trying again with 10.5. Gabe Suarez has been talking up the 10.5 for years. He is contreversial, but the concepts seem mostly valid on a non-SBR platform. It might be worthwhile to check out his concepts especially with SIG brace on the scene now.

[discreet]

Simply put, 10.3/5 in for 5.56 and 7, 7.5, 8 in 300blk.

If you cant find why you wouldn't want to use a 7.5 in on this forum using the search engine, you should slow down ar bit, and spend some time. This subject is so beat to death it's not funny.


The whole idea that you said you want reliability first, should immedialy scratch pistol length gas systems off your list. Shit, it should scratch 10.3/5 off your list also and just get an 11.5. Problem solved. Sure 10.3's and 5's will work great but honestly if you don't want to worry about anything just go with an 11.5 and be done with it. Or get a 10.3 DD barrel that has a slightly larger gas port so you can run more ammo types through it.

[scooter22]

The shortest viable bbl length on a 5.56 AR is 10.3".

As others have said: keep searching and reading.

[discreet]

What are you using for a muzzle device? I searched TONS of threads on TONS of websites, and it seems like the majority of folks running 10.3 and 10.5in barrels without a suppressor have a KX3 but it is heavy, A2, or Troy Claymore... but now we have the cheaper version of the KX3, the KAK flash can that I am hearing good things about.. Any recommendations?

A2 orif you want to waste money, get a blackout. Or if you get tired of killing your ears, a claymore. No reason to ever hang a boat anchor off your barrel unless it's a can off it.

a2 has been battle proven on the mk18. Nothing else to day. 8$ and works.

[Slvr Surfr]

What are you using for a muzzle device? I searched TONS of threads on TONS of websites, and it seems like the majority of folks running 10.3 and 10.5in barrels without a suppressor have a KX3 but it is heavy, A2, or Troy Claymore... but now we have the cheaper version of the KX3, the KAK flash can that I am hearing good things about.. Any recommendations?

I put a KAW Valley linear muzzle device on mine. It behaves much like the claymore and KAK can, directing noise and flash forward. It is not as long or heavy as the KX3 or KAK Can.

Check out the pistol picture thread for good ideas on what others are running.

[Clint]

A pistol with a KAK tube and Sig brace is practically an SBR, so recommendations would be the same for that question.

An excellent starting point for this is a LW 11.5" CAR upper backed up with an H2 buffer.


To answer some of your other questions:

The blast from a 10.5" barrel with an A2 flash hider is tremendous and the dwell time of the 10.5"/CAR is really shorter than optimum.

The 11.5"/CAR is a much better match.

The blast from a 7.5" will be even worse, but the pistol length gas system is actually a good match for this barrel length.

Linear style muzzle devices like our Covert Comp can significantly reduce the blast felt by the shooter.


The 5.56 cartridge is a poor match for very short barrels.

If the barrel must be very short, the 6.8SPC and 300BLK are more efficient choices.

In general, shorter gas systems have less tolerance for light buffers and large gas ports.

I've exhausted my google foo and cannot find the answers I'm looking for, so if a thread already exists that can help me, please point me to it.

I want to build AR pistol with a Sig brace. I have some questions I hope you guys can help me with.

My instinct for this "pistol" is to go as small and light as possible, so I'm thinking about a 7.5 inch barrel.

Are there any drawbacks with using the 7.5" barrel?

Any inherent problems with the pistol gas system compared to the carbine length?


However, reliability and overall handling are more important than size. Therefore I am wondering if I should go with a 10.5 or 11.5 inch barrel with a carbine gas system would be the smarter way to go?

Any advice would be appreciated.

I already own a couple of Noveske's and a Daniel Defense. So I understand the value of quality parts and manufactures. It looks like it would be really hard to beat the BCM 11.5 uppers with the Key Mode rail.

Thanks in advance.

[Hot Holster]

My 7.5" is a lot of fun to shoot with the pistol tube or with my NFA lower. It's quite accurate (not MOA, but good enough) at 25 yards and the pattern opens a bit at 50 yards. I have not had any reliability issues with PMC ammo being used.

I also have a 8" 300 Blackout and a 9.5" Blackout that I use suppressed, and hunt with.

For my personal uses, I would not go any longer than a 9.5"

[Ledanek]

The DD A2 that comes standard on the MK18. I have the BE Meyers on one of my HK rifles and it is VERY good but it is longer than I want on this setup.

Sir, Do you still use the BE Meyer?
Have you used it on your 10" rifle?
Can you share what is the length from barrel or OAL?
It's rare to read about BE Meyer, so I get excited, and have to ask. I'm in the "research phase" of building an AR Pistol. So far my collection of readings suggest to go with 10" as everyone has stated here.
In Illinois, the SIG Brace is accepted form of pistol. Still trying to verify the max round allowed.
I'll try to keep this between BE Meyer and length of barrel discussion for now.
thanks for your input.

[fferik]

In 5.56 I personally find 10.5 to be about right for a balance of ballistics and size. I had a 7.5, and while it was "fun" I don't find the 10.5 to be much more unwieldy, yet the ballistics are greatly improved. Well worth the trade off.

This thread has some good info on the subject:

https://www.m4carbine.net/showthread...15-reliability

[JusticeM4]

Definitely go with a 10.5" or longer pistol for better reliability. The SigBrace is a must if you don't go the SBR route.

I built a 10.5" with a H-buffer and it ran like a champ, no issues with a few hundred rounds. I used a standard A2 flash hider on it and the muzzle blast isn't as bad as most people say ( I shoot both indoors and outdoors ) as long as you are using good ear protection.

Check out the AR pistol pic page and see what people are running.