AR pistol, 7.5 vs 10.5?

[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:


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.

[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.

[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.

[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.

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.)