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View Full Version : 5.56 AR pistol....pros & cons of various barrel lengths?


Rorge Retson
10-08-2012, 8:38 PM
After much hemming and hawing and gnashing of teeth, I finally decided to go 5.56 for my new AR pistol build. :cool:

There were pros and cons to each of my finalists (.300 AAC, 6.8 SPC, 7.62x39), but in the end I decided that interchangeability with my other AR rifles was more important than any perceived advantage from the other choices.

So now the question is, what length barrel? I like the idea of smaller = better, but what are the tradeoffs? I know range will suffer the shorter I go, but how much? And will the bullet start to tumble if the barrel is too short?

What I really need to know is the effective range of the following barrel lengths for a 5.56 projectile:
- 7.5"
- 9"
- 10.5"
- 11.5"

Where can I find this info?

emptybottle151
10-08-2012, 8:53 PM
I'm interested in this as well.

wash
10-08-2012, 9:01 PM
The benefit of 10.5-11.5" barrels is that they are essentially "Commando" uppers which is what the carbine gas system was designed for, it should be about as reliable as an AR pistol can get.

I suggest you go for the fastest twist barrel you can find. With the reduced velocity of a short barrel, you won't spin a light bullet fast enough to make it fragment before it hits the target and if you try heavy bullets you're going to need all the twist you can get.

As far as effective range, what do you consider effective?

If it's just about accuracy, that can be pretty far.

If it's about energy, bullet expansion and penetration, I bet even the 7.5" would be pretty effective at 150 yards with a good hunting bullet.

If you consider a good wound effective, a 7.5" might be effective out to 300 yards or more even with ball ammo.

mif_slim
10-08-2012, 9:17 PM
7.5" would need tuning.

Rorge Retson
10-08-2012, 9:32 PM
I suggest you go for the fastest twist barrel you can find. With the reduced velocity of a short barrel, you won't spin a light bullet fast enough to make it fragment before it hits the target and if you try heavy bullets you're going to need all the twist you can get.

If it's about energy, bullet expansion and penetration, I bet even the 7.5" would be pretty effective at 150 yards with a good hunting bullet.

If you consider a good wound effective, a 7.5" might be effective out to 300 yards or more even with ball ammo.

Curious why most every 7.5" barrel I find is 1 in 9 twist, then...? :confused:

7.5" would need tuning.

Can you elaborate?

wash
10-08-2012, 9:43 PM
I think it's because they are cheap?

Quite possibly cut down rifle length barrels (maybe salvaging a batch with oversize gas ports?).

L4D
10-08-2012, 9:45 PM
Can you elaborate?

One way is to get an adjustable gas block to let just the right amount of gas for LRBHO.

mif_slim
10-08-2012, 10:16 PM
7.5" is producing too much pressure so your brass will get stripped. Like l4b said, tune your gas block or buy a H2+ buffer or both to tune the 7.5"...it gets annoying if you just want to shoot, but its fun to be able to tune it and have it working.

L4D
10-09-2012, 6:39 AM
7.5" is producing too much pressure so your brass will get stripped. Like l4b said, tune your gas block or buy a H2+ buffer or both to tune the 7.5"...it gets annoying if you just want to shoot, but its fun to be able to tune it and have it working.

The biggest difference was how much flatter the 7.5" got after choking the gas.

not as flat as my rifle with an adjustable gas block but at least its not wanting to jump out of my hands anymore, lol.

Rorge Retson
10-09-2012, 7:20 AM
Here are a couple of barrels, one Parkerized with a 1-in-9 twist, another Melonited with a 1-in-7 twist:

AR-Stoner 7.5" 1-in-9 Twist Barrel
http://www.midwayusa.com/product/138292

http://media.midwayusa.com/productimages/880x660/primary/138/138292.jpg

Adams Arms 7.5" 1-in-7 Twist Barrel
http://www.riflegear.com/p-1325-adams-arms-75-melonite-pistol-barrel.aspx

http://www.riflegear.com/images/product/large/1325_1_.jpg

So now I wonder, is the 1-in-7 Melonited barrel going to be that much better than the significantly less expensive 1-in-9 Parkerized barrel? What do you guys think?

starsnuffer
10-09-2012, 8:07 AM
It's an AR pistol, IE plinking toy. Better relates to how much fun you're going to have with it, you decide.

-W

edrex
10-09-2012, 8:15 AM
Tagged

Rorge Retson
10-09-2012, 8:47 AM
7.5" is producing too much pressure so your brass will get stripped. Like l4b said, tune your gas block or buy a H2+ buffer or both to tune the 7.5"...it gets annoying if you just want to shoot, but its fun to be able to tune it and have it working.

The biggest difference was how much flatter the 7.5" got after choking the gas.

not as flat as my rifle with an adjustable gas block but at least its not wanting to jump out of my hands anymore, lol.


Okay, question - once I get it "tuned" properly, will I need to tune it anymore? Or will it be Tune It and Shoot It!?! :)

L4D
10-09-2012, 8:51 AM
I've taken my 7.5" out to 100 yards with no tumbling using factory ammo.

It's not fun to shoot off hand nor is it fun to ram the pistol tube into your shoulder shot after shot.
Most people aren't sure why they have an AR pistol... :)

Okay, question - once I get it "tuned" properly, will I need to tune it anymore? Or will it be Tune It and Shoot It!?! :)

You tune it to the ammo your shooting. If you swap ammo it may not cycle completely, especially if you go to a weaker cartridge.

Rorge Retson
10-09-2012, 9:12 AM
I've taken my 7.5" out to 100 yards with no tumbling using factory ammo.

Awesome, thanks. :)

Most people aren't sure why they have an AR pistol... :)

HD?

You tune it to the ammo your shooting. If you swap ammo it may not cycle completely, especially if you go to a weaker cartridge.

Ah, gotcha. :D

phdo
10-09-2012, 9:17 AM
I have a 7.5" barrel. Works like a charm.

gun toting monkeyboy
10-09-2012, 9:37 AM
The advantages to the shorter barrels is that they are handier. The trade offs are a serious reduction in performance and the need for a special gas system. And don't expect any of the hunting bullets other than possibly the thinnest jacketed varminting rounds to expand at all with the velocities you are likely to see coming out of something that short.

The longer pistol barrels offer a several hundred feet per second advantage in velocity. The difference between 11.5 and 10.5 is huge, if the various studies online are to be believed. The shorter barrels are even worse. If all you are looking for is a range toy, pick what you want. If you want to get the most out of it that you can, consider the longer barrels. I have a 10.5" upper that I have been using for several years, and I am quite happy with it. I also have a 13" upper that I set up like an Israeli Menusar, and that performs much more like a rifle than a pistol. It is on par with many of the 16" carbines in terms of accuracy. Truthfully, I would be comfortable using either upper on coyotes and such with good hunting bullets. I don't know if I would be as comfortable with the 7.5" barrels.

My next project for "someday soon" is an 11.5" upper, so that I can test out how accurate the various studies I have seen online are. I really want to know if that spike in velocity they have noted between the 11.5" and 10.5" barrels is real.

-Mb

itisagoodname
10-09-2012, 9:45 AM
I have 4x pistol uppers that are built and functioning. All are very accurate out to 50yds (max ive tested so far). I have not noticed a difference between the 1/7 and 1/9 twist at that distance. The piston upper sure feels nice though!

It would be nice to test through a chrono but i dont know of anyone with one. I dont reload so i dont have much of a use for one.

I have one more 6.5" 1/7 barrel i will be installing onto another upper soon. My next builds will all be dedicated 22lr uppers.

gun toting monkeyboy
10-09-2012, 9:47 AM
I have 4x pistol uppers that are built and functioning. All are very accurate out to 50yds (max ive tested so far). I have not noticed a difference between the 1/7 and 1/9 twist at that distance. The piston upper sure feels nice though!

It would be nice to test through a chrono but i dont know of anyone with one. I dont reload so i dont have much of a use for one.

I have one more 6.5" 1/7 barrel i will be installing onto another upper soon. My next builds will all be dedicated 22lr uppers.

What barrel lengths?

itisagoodname
10-09-2012, 11:00 AM
What barrel lengths?

1 @ 7" 1/9
1 @ 7" twist unknown
1 @ 7.5" 1/9
1 @ 7.5" twist unknown
1 @ 6.5" 1/7

Munny$hot
10-09-2012, 11:37 AM
IIRC using FMJBT M193 55gr a 11.5 barrel 1/7 will fragment @ 50 yards. A 10.3 barrel 1/7 @ 15-25 yards. As far as accuracy the shorter the barrel the faster the bullet velocity drops off, so depending on the wind conditions your grouping will vary. Hitting targets @ 150 yards reliably would be do-able from a 10.5 - 11.5 barrel. If your worried about stopping power you can always load or buy special purpose rounds, just do your homework as far as the velocity needed for the bullet to expand.

Here is a great link the has some comparisons of different lengths with different loads
http://www.ar15.com/archive/topic.html?b=3&f=118&t=509733

bloodhawke83
10-09-2012, 12:48 PM
I'd go 1/7 with any 556 barrel. at 7.5", 1/9 wouldn't give the bullet a full turn.

wash
10-09-2012, 12:51 PM
I've taken my 7.5" out to 100 yards with no tumbling using factory ammo.

It's not fun to shoot off hand nor is it fun to ram the pistol tube into your shoulder shot after shot.
Most people aren't sure why they have an AR pistol... :)



You tune it to the ammo your shooting. If you swap ammo it may not cycle completely, especially if you go to a weaker cartridge.
I have a 7.5" .458 SOCOM AR pistol.

I shoot with an ~isosceles stance, no shouldering, iron sights.

It kicks but beside a little hot spot from the A2 pistol grip, it is not uncomfortable.

mif_slim
10-09-2012, 1:30 PM
7.5" will expand for its intended use. I tested 55gr PSP at 20 yards which is CQB distance for me and the bullet went thru 4 wet phone books and the jacket open about 3-5" into the books. Pretty nice if you ask me.