7.5" vs 10.5" AR pistol

[justonemorear]

Reguardless the length, invest in a

Noveske KX5 5.56 Flash Suppressor (Flaming Pig)

They are worth it.
You are pretty much building a flamethrower
I built them from 5" out and a good comp/brake to directional the report forward is needed

 

[Toxic6]

I put one together with a 7" barrel, pws cqb really helps with the flash issue. It's set up with a pdw brace and a binary trigger and doing a drum dump is a good stress reliever . Idk about reliability issues but really wishing I'd used a pin on gas block it's really disappointing when after 2-300 rounds all the sudden it's a single shot

If your going for compact go for compact…if your going for ballistics and accuracy go with a rifle not a pistol

 

[titsonritz]

Idk about reliability issues but really wishing I'd used a pin on gas block it's really disappointing when after 2-300 rounds all the sudden it's a single shot

Are you say you have issues with the gas block moving and cutting off the gas port? If that is the case, dimpling the the barrel, using a knurled set screw and 271 red Loctite will fix the problem...

https://slrrifleworks.com/750-dimpling-jig/

 

[Toxic6]

Are you say you have issues with the gas block moving and cutting off the gas port? If that is the case, dimpling the the barrel, using a knurled set screw and 271 red Loctite will fix the problem...

https://slrrifleworks.com/750-dimpling-jig/

Yeah it's got a dimple already, just didn't have loctite…I used some vibratite and then lightly staked it haven't had the issue repeat yet

 

[The Heretic]

I'd stick with 10.5, I've owned both. The 7.5 will be louder and the shorter barrel will neuter the round's performance quite a bit. Like half.

It would essentially make it the equivalent of a 5.7x28 from a PS90/P90

 

[kmk1012]

just didn't have loctite

You could always use "Farmers Loctite", you never run out of it, just a little plier crimp on the threads just before they go in, LOL. Never come loose!

 

[Hardcore_rucke]

Hey guys, so I decided finally to go for a 10.5" upper from PSA. My question now is, how necessary is a muzzle device upgrade, and what do folks reccomend and why? Thanks in advance, everyone's responses so far have been very insightful.

 

[Toxic6]

Hey guys, so I decided finally to go for a 10.5" upper from PSA. My question now is, how necessary is a muzzle device upgrade, and what do folks reccomend and why? Thanks in advance, everyone's responses so far have been very insightful.

I 100% recommend a PWS CQB device unless you're going to run a can on it…I'm sure you'll get other input but those have been my go to for short barrels for a long time

 

[OldTengu]

I have 7.5 and 10.5 ARs.
Both are fun. I've rung steel out past 100 with both.
7.5 is louder. 10.5 maintains ballistic performance better.

 

[Member 53328]

Hey guys, so I decided finally to go for a 10.5" upper from PSA. My question now is, how necessary is a muzzle device upgrade, and what do folks reccomend and why? Thanks in advance, everyone's responses so far have been very insightful.

Whatever you do, DONT get a compensator.

 

[Hardcore_rucke]

Whatever you do, DONT get a compensator.

Why is that?

 

[Diamondback]

Why is that?

Because they make already hellacious unsuppressed blast even worse. Linears direct it downrange, but if you're shooting indoor the walls will turn that concussion wave right back around to you.

Only rifle-caliber I'd wanna deal with in 7.5 is maybe subsonic .300BLK, which was designed for short barrels, and even then I'd really prefer an inch or two more.

 

[Member 53328]

Why is that?

If you have any friends right now you won't after buying one of those.

 

[ilikegunspdx]

That's where .300 BO comes in.

A 12.5" is the happy spot for a 5.56 "pistol", IMO...

I'm no expert but I agree with both of titsonritz's posts above based on all the research I've done and listening to bonafide experts (I went down the research rabbit hole ha ha when trying to figure out what I wanted for compact 556 gun). I have always considered 12.5" the sweet spot for 556 barrel length when going for compact gun.

According to Clint smith of thunder ranch "God and Stoner designed the rifle for a 20 inch barrel", meaning that's where max effectiveness of the round is. Anything less is a compromise and it's a matter of how much u are willing to give up in terms of velocity. As KruelJ said velocity decrease at 7.5" is massive. I have a chart of % velocity energy loss for 223/556 with barrel length somewhere I can dig up if u want. pasted at bottom of this post.

Another thing to consider in terms of compactness is u can eliminate a ton of length by not having a buffer. Foldable/collapsible weapons such as rock river arms, sig virtus, ar-180, etc can be stowed and also function with stock collapsed or folded. Even 16" guns with folded stocks such as hk 43, sig 556 are considerably smaller than standard AR 16" with buffer. So that can factor into overall compactness and chosen barrel length too.

For me my ideal would be sig virtus 12.5" or brn-180 if they made it in 12.5". I chose brn-180 in 10.5" length due to that is all they make for compact. Other reasons I chose brn-180 fwiw: 1) low cost (compared to sig and some other high end bufferless guns) 2) uses standard AR15 lowers, triggers, and mags 3) uses proven ar-180 short stroke piston system that has been used in many guns such as HK 416 etc., 4) ability to use with stock/brace folded such as in a vehicle etc.

FWIW I don't see any difference in accuracy when shooting brn-180 vs standard AR 16" head-to-head at close to intermediate ranges (have not tested at longer than 100 yards). I much prefer the recoil impulse of the brn-180 and lack of "twang" or vibrations from the buffer tube. All just my experience fwiw and everybody has their own experiences.

A couple pics of brn-180 in 10.5" size FYI:


Also FYI some pics of more exotic bufferless options such as hk 43 (16" barrel). Also a foldable AR15 system with buffer but does not function when folded. I didn't pursue any of these due to cost (around $2k) personally:
Sig virtus 12.5"

Foldable non functioning when folded:

Shorter barrel version of the same:


Some others (does function when folded/collapsed):


Edit: found the % energy loss chart I compiled from a few online sources fwiw:

Edit: law tactical folding adapter should be mentioned as a way to reduce overall length also but I haven't researched it enough to know much about it in terms of reliability/function etc.

 

[CZrespecter]

I'm looking to build an AR pistol. Can't decide whether to go with a PSA blemish 10.5" upper or a CBC blemish 7.5" . They are about the same price, I've heard that 7.5 is louder but is it that much of a difference? Any other considerations?

Never go under 10.3" in 5.56 unless it's for a BS plinker not enough velocity on the round and increased parts wear isn't exactly what you'd want on a "work" gun.

 

[Hardcore_rucke]

I decided on the 10.5" PSA upper. Got it together yesterday, and ran a few rounds through it today! Stoked! Thanks for all the information, guys.

 

[titsonritz]

So why are we even talking about pistols then? 12.5 is almost pointless for any real reason to build one.

It is a pretty big difference over a 16", which most do to avoid the pinning thing. I built a GAU-5A 'ish pistol with a 12.5" and difference over a 16" is even more pronounced. I discovered a 12.5" barrel and a lower with a standard carbine buffer (I would normally use an A5 buffer) fully collapsed is a spot on equal match in overall component length. I'll probably add a 9" .300 BO for a more pistolesque alternative. I need to get some comparison pics together one of these days.

Dude that's barely a "pistol". You need to SBR both of them!

I need to put up some pics of 12.5"

Pic are here...
https://www.northwestfirearms.com/t...val-rifle-enters-service.299851/#post-3231290