AR pistol, 7.5 vs 10.5?

[odmichael]

What do you guys recommend? Do the extra inches matter?

This'll be my first and I want to make sure I've got some info before I dive into this project.

Thanks [BD]

[Ride4frnt]

If I had to guess, you're going to get a general consensus of 11.5". Plenty of people have 10.5" but the reliability of 11.5 is much higher.

[GOST]

To me 7.5" is short for 2 reasons. 1 is that you won't have much real estate on the handguard for grip, you'll be all scrunched up. 2 is that it's gonna be very loud for the shooter. I agree with Ride on the 11.5" or maybe even a 12.5". For 5.56 I wouldn't go shorter than 10.3", but if your wanting to go really short you may want to try a 8.2" 300 BO.

[JoshAston]

I'm gonna go against the grain and say 7.5" because it's fun. They don't have much practical use, but they'll put a grin on your face!

[MonkeyBomb]

I have a 7.5. It's loud as hell. I mean concussively loud to anyone around you. Still Fun. I wished I would have gone 10.5 at least. anything under 10.5 will give you a good chance of blowing up an expensive suppressor and cause you to start all that paperwork again.

[VIPER 237]

Dwell time is stupid short on the 7.5 and they are finicky with different ammo, parts take much more abuse, its louder than hell and even though some suppressors can handle that short of barrel they are not hearing safe, ballistics are pitiful, and unless youre 5'5" the hand guard is too short.

10.3/5 is the shortest i'll ever go with the 5.56, but 11.5 is the sweet spot for me, I cant remember the exact spec but I think the extra inch from 10.5-11.5 give you close to 30% increase in dwell time.

[voodoo_man]

both?

[WHSmithIV]

I decided 10.5" for the 7.62x39 pistol I'm building. The main reason for that is because at 7.5" I'd have a serious flame thrower. It may still end up being a flame thrower, but not as much of one.

[AR-10]

I had a 7.5" upper on my pistol and it was SEVERELY overgassed.

I got rid of it and bought a DD MK18 upper.

[toolboxluis00200]

i have a 10.5 SBR and that is very very light easy to shoot and after i added a spike tactical Krink very controllable


http://youtu.be/-qrhS67-jgg?list=UUYPQcqzNNfA6WMUHATPaXJg

[Pyzik]

If I had to guess, you're going to get a general consensus of 11.5". Plenty of people have 10.5" but the reliability of 11.5 is much higher.

This. I went through what your're going through now.
10.5" was decided as short as I would go. I'd go 11.5 if I could get away with it. But funky laws here in MI are keeping me at 10.5 due to OAL issues.

[Uffdaphil]

OP doesn't specify caliber. Huge difference between 5.56 and 30 cal (7.62 & 300BLK). Larger bore allows shorter efficient length. 8.5 & 9" are standard short barrel Blackout lengths. I can't see 7.5" being radically different in performance in the larger calibers.

I have a 7.5" 5.56 pistol that has not given me problems (linear comp a must IMO), but I still wouldn't trust it as a primary defense weapon unlike my longer pistols.

[Kopis]

Do the extra inches matter?

[BD]

Yes, why yes they do... just ask any lady!




I'm gonna go against the grain and say 7.5" because it's fun. They don't have much practical use, but they'll put a grin on your face!

That being said, what's your purpose for this gun? If it's just a fun gun, definitely go 7.5"!!! KX3 flaming pig comp does take some of the crack out but any pistol will be loud. I did the 7.5" because i wanted a compact PDW without a tax stamp. I can carry a lot of firepower in a small package.... and it's just a freaking blast to shoot. Everyone loves it.


I keep hearing about reliability issues with AR pistols but my two shooting buddies and I each have built a 7.5". all three different brands and we've all run lots of different ammo through them and never ever had a hiccup of any kind so i dont know if that's an older issue or what. I know the first AR pistol barrels had the same size gas port as a rifle which was causing dwell issues but most new pistols are utilizing a larger diameter gas port which has alleviated those reliability concerns to my knowledge.

I highly recommend the 3.5" extended buffer tube and sig brace. Really helps with the length of pull. Law Tac folding attachment point added another inch. Perfect now.

http://i568.photobucket.com/albums/ss126/Papachristou/2014-09/80E2096F-D226-4A5C-8423-B44B24C5AC3B_zpszu6rvdh6.jpg (http://s568.photobucket.com/user/Papachristou/media/2014-09/80E2096F-D226-4A5C-8423-B44B24C5AC3B_zpszu6rvdh6.jpg.html)

http://i568.photobucket.com/albums/ss126/Papachristou/2014-08/1EAE1587-5F78-4C38-95F0-B15240FE3E13_zpsal7hzrqx.jpg (http://s568.photobucket.com/user/Papachristou/media/2014-08/1EAE1587-5F78-4C38-95F0-B15240FE3E13_zpsal7hzrqx.jpg.html)

[UWone77]

Never owned anything shorter than 8.2" (300 BLK). The 7.5" I've shot needed to be tuned for the most part.

However, I decided to try out the 7.5" from Aero.

[GHOSTMAN]

Nice ar pistol

[toolboxluis00200]

Never owned anything shorter than 8.2" (300 BLK). The 7.5" I've shot needed to be tuned for the most part.

However, I decided to try out the 7.5" from Aero.

i have bin looking in to that one for the price very tempting

[WHSmithIV]

OP doesn't specify caliber. Huge difference between 5.56 and 30 cal (7.62 & 300BLK). Larger bore allows shorter efficient length. 8.5 & 9" are standard short barrel Blackout lengths. I can't see 7.5" being radically different in performance in the larger calibers.

I have a 7.5" 5.56 pistol that has not given me problems (linear comp a must IMO), but I still wouldn't trust it as a primary defense weapon unlike my longer pistols.

7.62x39 and .300 Blackout though are quite different rounds. .300 Blackout was designed to be subsonic ammunition and to be suppressed. No so with 7.62x39. This is why the short barrels are quite standard for .300 Blackout. The 7.62x39 is going to create substantially more gas than subsonic .300 Blackout rounds. AK47's have been created as pistols and are very much flame throwers with short barrels. I watched a youtube video of a guy firing a 7.62 AR pistol with a 7.5" barrel and there was plenty of flame. Every inch of the barrel allows for more powder to burn rather than have it burning in the air around the end of the barrel. I'm hopeful that 10.5" will be just enough to let most of the powder get burnt for 7.62x39 though I don't have data to know for sure how much flash there still will be. It will be quite a bit less than with a 7.5" barrel though.

[Kopis]

WHSmithIV,

You have a really good point about the blackout. I remember reading it has very little fall difference whether you're using a standard 16" barrel versus a shorter SBR/pistol length barrel. It could've been that the velocities were very similar too, i cant remember the article 100%.

My friends AK pistol is a ground thumper and flame thrower. Insane fireballs!

[WHSmithIV]

WHSmithIV,

You have a really good point about the blackout. I remember reading it has very little fall difference whether you're using a standard 16" barrel versus a shorter SBR/pistol length barrel. It could've been that the velocities were very similar too, i cant remember the article 100%.

My friends AK pistol is a ground thumper and flame thrower. Insane fireballs!

I have a ballistics data link somewhere for .300 Blackout with muzzle velocities for different barrel lengths. I'd have to look it up never mind - I found it. Here it is:
http://img692.imageshack.us/img692/3653/screenshot20120210at814.png

Note that the .300 blackout data here is for supersonic ammo, not subsonic.

[Kopis]

yeah, looks like 1/3 less FPS loss than a 556. i cant remember exactly how the article phrased it but they said the shorter lengths had little effect on the blackout's stopping power at longer ranges.

[Pyzik]

yeah, looks like 1/3 less FPS loss than a 556. i cant remember exactly how the article phrased it but they said the shorter lengths had little effect on the blackout's stopping power at longer ranges.

This.
It's not all about muzzle velocity.

[Kopis]

Yeah, it's been awhile that's why i said i wasn't sure how to explain it. At any rate, love my blackout. Use it for sub 100 yard coyote hunting. Never has failed to take one down on the first shot (as long as i dont miss!) i use those 110gr horandy vmax rounds.

[WHSmithIV]

If you look at it, you're losing ~200 FPS in muzzle velocity with .300 Blackout going from a 16" to 8.5" barrel. Figuring what the stopping power is over 100 yards, there isn't much difference since the bullet is a .30 caliber bullet. There are so many other factors involved than just muzzle velocity when thinking of stopping power over distance. Shot placement and accuracy being foremost followed buy bullet drop and drag. Shoot a bad guy in the eye at 400 yards with a .233 and he'll be very stopped dead - just as dead as if you shot him at 100 yards. Shoot him in the shoulder with a .303 Lee Enfield at 200 yards and you blow a hole out the back of the shoulder the size of a golf ball provided you miss all the bone. .300 Blackout would do the same at around 100 yards. That's the hydraulic shock effect. At 25 or 50 yards the .45 pistol does the same thing.

With the .223, you are losing ~600 FPS going from a 16" barrel to a 8.5" barrel but the muzzle velocity is still higher than the .300 BLK from a 16" barrel. All else being equal (which they never are with ballistics), muzzle velocity means a bullet should travel farther therefore having more accuracy over distance. Too may other factors come into play though the instant a bullet leaves the barrel for that to actually be true.

[mustangfreek]

I have nothing good to add, except just kinda finished my first short barrel, 10.5" RA barrel, in pistol form right now..Had a glitch at first, but since then and the 2 times i have been out since, it has ran flawless with any ammo...

For me , im not sure id do a 7.5" setup, i have long arms and the 10.5" seems perfect,wouldnt want to go any shorter

[CarbonScoring]

Never owned anything shorter than 8.2" (300 BLK). The 7.5" I've shot needed to be tuned for the most part.

However, I decided to try out the 7.5" from Aero.

I've got a 10.5" Aero barrel in my pistol. It's run great so far.

https://farm4.staticflickr.com/3938/15628945092_957fb09ce9_b.jpg

[JHoward]

I have an 11.5" BCM pistol that has proven handy and reliable enough that it has taken the position of my "night stand" gun, although I fully expect myself to be deaf if I ever have to use it. I also had a 10.5 MAS Defense barreled upper that was great and never had any type of issue.

http://tapatalk.imageshack.com/v2/14/11/14/8ce128205c0b351ec2f015e530bd95a1.jpg

[UWone77]

Aero Precision 7.5" Upper.

I find that it's just really loud, and more of a range toy upper than something I'd want to carry around in pistol form. However, as a SBR upper, it's a lot of fun.

http://i1016.photobucket.com/albums/af282/richdkim77/IMG_2550_zps93f4f599.jpg (http://s1016.photobucket.com/user/richdkim77/media/IMG_2550_zps93f4f599.jpg.html)

[Ride4frnt]

I have an 11.5" BCM pistol that has proven handy and reliable enough that it has taken the position of my "night stand" gun, although I fully expect myself to be deaf if I ever have to use it. I also had a 10.5 MAS Defense barreled upper that was great and never had any type of issue.

http://tapatalk.imageshack.com/v2/14/11/14/8ce128205c0b351ec2f015e530bd95a1.jpg

Glad to hear that. I was looking at MAS defense barrels for a budget pistol.

[Gaspipeshooter]

The biggest factor in my decision to go with an 11.5" barrel on my pistol build was the information from Paul Buffoni at BCM regarding dwell time and the effect it has on reliability. I also factored in the velocity information I've seen regarding the lack projectile energy and fragmentation with shorter barrels. I'm a very practical minded person; to me, in real life the difference between an 11.5" and a 10.5" barrel isn't even worth considering. While they might be nice "toys", a 7.5" barrel length AR in .223/5.56 has no attraction to me.

[Uffdaphil]

I wonder if anyone has calculated how much dwell time is added using a linear comp (closed tube) like the KX5 on a 10.5". Paul Buffoni's stated 40% for the extra 1" bore length is the reason I have a flash hider on the 11.5" and Claymore on the 10.5". Perhaps the KX5 is the reason my 7.5" has cycled reliably. (Still the last AR I would grab for defense until many more rounds evidence dependability.)

[JHoward]

Glad to hear that. I was looking at mad defense barrels for a budget pistol.

I would not hesitate to use them again. The shipping was really quick and their customer service was top-notch. I had a ton of questions and they answered them all through email very quickly. I have referred quite a few people to them and they have all been happy with their barrels.

[voodoo_man]

relevant to convo:

http://vdmsr.blogspot.com/2014/11/range-report-for-mk107p.html

The shorter the barrel, the more finicky the accuracy.

[JHoward]

As far as accuracy, as far as I can tell, my 11.5 is at least as accurate as my 14.5" out to 100 yards. My 10.5 MAS defense barrel was non chrome lined and it was just as accurate as them both.

[Gaspipeshooter]

relevant to convo:

http://vdmsr.blogspot.com/2014/11/range-report-for-mk107p.html

The shorter the barrel, the more finicky the accuracy.

Good stuff in that review.

[voodoo_man]

Good stuff in that review.

Hopefully I can get some Useful data out of this whole thing.

[six8]

I don't experience a sound difference between my 7.5", 11.5" or 14.5". Are y'all using foam ear plugs?

[CarbonScoring]

I always double up the ear-pro when shooting rifles. I also don't notice a difference between my 16", 14.5" or 10.5" while I'm the shooter. I do notice a difference when another shooter is next to me with a shorter barrel.

[voodoo_man]

Always double up.

You'll thank yourself for doing it when your 60.

[Computalotapus]

Always double up.

You'll thank yourself for doing it when your 60.

Huh? Man I will be 40 next month. I am pretty sure I am a bout 80% deaf in my right ear due to a 60 being fired next to me for an extended period of time. My dad keeps telling me to get on disability for hearing loss but the way I see it is that there are more needing vets that need that appointment than I do. I double up on ear pro to save what little I have left.

[voodoo_man]

Huh? Man I will be 40 next month. I am pretty sure I am a bout 80% deaf in my right ear due to a 60 being fired next to me for an extended period of time. My dad keeps telling me to get on disability for hearing loss but the way I see it is that there are more needing vets that need that appointment than I do. I double up on ear pro to safe what little I have left.

Had a guy discharge inside a 4x5 living room next to my right ear (aiming behind me), I couldn't hear out of that ear for a good 3 days. Doc told me it'll be max 90% never better after that, but I'm not going out on disability just yet.

I always double up, I carry some of the surefire ear plugs with me, EDC, just in case.

[Gaspipeshooter]

I had a guy touch off a 3.5" 12 ga. waterfowl load about a foot from the side of my head a few years ago. Felt like someone whacked me upside the noggin with a 2x4. I was almost completely deaf in that ear for a few days. Gradually my hearing started to come back, but it's no where near 100%, nor will it ever be.

[WHSmithIV]

I'm definitely going with the 10.5" barrel for the 7.62 pistol. I've also changed the plan to get the Faxon barrel since it has a carbine length gas port. (Thanks UWone for that tip). I have been a bit concerned with the designing of the pistol that a pistol length gas port would seriously over gas the gun. With the Faxon barrel I think the design now has the right balance with not using an adjustable gas block.

[Kopis]

relevant to convo:

http://vdmsr.blogspot.com/2014/11/range-report-for-mk107p.html

The shorter the barrel, the more finicky the accuracy.


Sure, barrel length affects accuracy, same way a ruger LC9 isnt as accurate as my g34... I think people need to keep in mind that an AR pistol isn't supposed to be a sniper rifle. Its function is that of a close range PDW. 10-100 yards max. My 7.5" pistol has no problem ringing 8" steel at 100 yards with a simple PA red dot. I haven't benched it to check groups because i don't need or expect sub MOA accuracy from this type of weapon.

[voodoo_man]

Sure, barrel length affects accuracy, same way a ruger LC9 isnt as accurate as my g34... I think people need to keep in mind that an AR pistol isn't supposed to be a sniper rifle. Its function is that of a close range PDW. 10-100 yards max. My 7.5" pistol has no problem ringing 8" steel at 100 yards with a simple PA red dot. I haven't benched it to check groups because i don't need or expect sub MOA accuracy from this type of weapon.

I disagree when it comes to rifles.

Pistols, yes, barrel length does in fact matter but not for rifles.

I am more than sure my 7.75inch barrel can put up good groups at 100y with the right ammo, and I am also positive I can hit out to 200y and even 400y with the right optics and the right ammo. The trick is to find what works for that specific setup.

[JHoward]

While I have you here, is the claymore noticeably more quiet from the rear and sides compared to the regular FH on your 11.5?

*oops. I was back three pages replying to this.