AR Sponsor
Posted: 1/7/2009 7:39:28 AM EDT
| Im sorry if Im asking a commom question but I have searched the forum with no luck finding an answer. I want to put together a AR pistol but am not sure what barrel length to go with.The 7.5" length looks really good but how would a 1/9 twist perform? Or would there be a more dramatic increase with a 10.5" in 1/9? Any input would be appreciated. |
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I'm not sure if your asking about power or accuracy. Both will suffer somewhat in shorter barrels.
When it comes to bullet speed and energy...most statics are either based on 20" barrels or 14.5" barrels. Civilian bullet manufacturers use the longest to give the uppermost stats. Military manufacturers test with 14.5" since this is the most common cabine length found in the Military. A general rule of thumb reported by people who test this stuff here on ARF.com is you loss about 100 ft/sec for every inch of barrel you cut. Not sure about ft/lbs but since it's based on the speed more than the weight of the round in 5.56 it will suffer as well. There has been some talk about fragmination but people here have been kind enough to do fragmentation tests that show a 55gn round WILL fragment out of a 7" barrel. Accuracy will suffer when you shorten your sight radious and also because you barrel may tend to "dance" on you a little being shorter. There is also a reliablity factor to consider with pistol length (7" and 7.5" barrel length) gas systems. With the shorter system reliablity can become a factor. Most here agree that a heavy buffer will address much of this if encountered. Even still if this is intended to be a defence rifle a 10.5" or 11.5" might be a better option since they use carbine gas systems. If it's gonna primarily be a range toy then 7"'s are a blast! Hope this answers your question. |
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I'm not sure if your asking about power or accuracy. Both will suffer somewhat in shorter barrels. No, accuracy will not suffer. Quoted:
A general rule of thumb reported by people who test this stuff here on ARF.com is you loss about 100 ft/sec for every inch of barrel you cut. The difference between 20 and 16 is 200 feet per second. The difference between 11 and 7 is larger. The only solution is to actually look it up. Quoted:
Accuracy will suffer when you shorten your sight radious and also because you barrel may tend to "dance" on you a little being shorter. AR pistols are full of fail, but trying to use conventional sights is just asinine. |
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I'm not sure if your asking about power or accuracy. Both will suffer somewhat in shorter barrels. No, accuracy will not suffer. Quoted:
A general rule of thumb reported by people who test this stuff here on ARF.com is you loss about 100 ft/sec for every inch of barrel you cut. The difference between 20 and 16 is 200 feet per second. The difference between 11 and 7 is larger. The only solution is to actually look it up. Quoted:
Accuracy will suffer when you shorten your sight radious and also because you barrel may tend to "dance" on you a little being shorter. AR pistols are full of fail, but trying to use conventional sights is just asinine. So your as accurate with a 7" as you are with a 16" @ 100yds?  I said general rule of thumb when it came to speed, depending on ammo it could be anywhere from 50-150 ft/sec per inch of barrel loss.  And you and I whole heartedly agree on the sights...but I haven't scraped together enough for an Aimpoint or EOTech yet so... 
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| For now I went with a 10.5 barrel. I may be able to work up a half decent load with the CAR gas length. I probably will still put together a 7" upper but will wait for parts to be more available. Im on a list for a couple of lowers so I have some time. Thanks again for the input. |
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'hell, I know I can hit an apple at 50m standing... With irons... on my 10.5"
I shoot clay pigeons all day as well. Prone, I can hit em at 100m regularly. a 10.5" is just as accurate as my 16"... but this isn't about how accurate a person is shooting it––- it's about how accurate the gun is on its own. all you really have to worry about is the extra drop from the loss of velocity... no harm with some practice––- get to an appleseed shoot, you'll love ar-15 irons after that. |
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So your as accurate with a 7" as you are with a 16" @ 100yds? Yes. Quoted:I said general rule of thumb when it came to speed, depending on ammo it could be anywhere from 50-150 ft/sec per inch of barrel loss.
Understood. Still not as good as looking at a velocity curve. |
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If you are planning to use an AR in 5.56/.223 to shoot flesh (men, animals, zombies, etc.), you will want the bullet to fragment. A .223 bullet that doesn't fragment is like a .22 LR or .22 magnum.
To achieve velocities capable of fragmentation, you will need a decent barrel length. There are many threads that have popped up in the past couple of months about fragmentation and barrel length in this very forum. To get reliable fragmentation at 50 yards or so with 5.56 TAP ammo, you will need an 11.5" barrel at least. That made me abandon the 5.56 pistol build altogether. I went with a 9mm AR pistol, so I could use heavier/bigger bullets that expanded (hollow points, etc.) and not have to get a long barrel and rely on fragmentation for stopping ability. As mentioned above, AR pistols are often "full of fail" but only in 5.56/.223. Shorty 9mm ARs work fine, as would about any other pistol caliber as a man-stopper. All AR pistols make fun range toys, however. 
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I've never once hunted with a fragmenting bullet...
If I'm shooting flesh, I'm going to use a Hunting round, which will expand and mushroom (not frag) To about the size of a .45, going 2.5x the speed of my 45. Out of my 10.5" barrel, i've had full expansion of my hunting rounds at 100m using the super scientific method of a box full of water, well, two of them. Barnes Triple shock 70gr are the bullets that I load and which are referenced above... Shorty AR's only fail w/ FMJ ammunition... hell, even a 69gr SMK will have partial to total fragment at 100m out of a 10.5, I've done it first-hand... |
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If you are planning to use an AR in 5.56/.223 to shoot flesh (men, animals, zombies, etc.), you will want the bullet to fragment. A .223 bullet that doesn't fragment is like a .22 LR or .22 magnum. I guess you should call up all the SoF guys shooting TSXs and let them in on the secret. Quoted:
That made me abandon the 5.56 pistol build altogether. I went with a 9mm AR pistol, so I could use heavier/bigger bullets that expanded (hollow points, etc.) and not have to get a long barrel and rely on fragmentation for stopping ability. That is ass backwards. A 9MM AR pistol? What is wrong with a Glock 34? |
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If you are planning to use an AR in 5.56/.223 to shoot flesh (men, animals, zombies, etc.), you will want the bullet to fragment. A .223 bullet that doesn't fragment is like a .22 LR or .22 magnum. I guess you should call up all the SoF guys shooting TSXs and let them in on the secret. Quoted:
That made me abandon the 5.56 pistol build altogether. I went with a 9mm AR pistol, so I could use heavier/bigger bullets that expanded (hollow points, etc.) and not have to get a long barrel and rely on fragmentation for stopping ability. That is ass backwards. A 9MM AR pistol? What is wrong with a Glock 34? Because glocks don't freak out lib-tards nearly as much as ARs. 
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Quoted:Because glocks don't freak out lib-tards nearly as much as ARs.
And because Glocks aren't AR pistols. I wanted an AR pistol that could share mags with my 9mm AR carbine. You bought a 900 dollar pistol instead of a 500 dollar pistol so you could save 400 dollars on magazines? |
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You bought a 900 dollar pistol instead of a 500 dollar pistol so you could save 400 dollars on magazines? No, I BUILT (only noobs BUY ARs) an AR pistol that is basically an SBR without a stock body. I can't shoulder or get a cheek weld on my Glock. I had the money and wanted a toy. It's still a free country for a little while longer anyway, so I can do as I please. |
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You bought a 900 dollar pistol instead of a 500 dollar pistol so you could save 400 dollars on magazines? No, I BUILT (only noobs BUY ARs) an AR pistol that is basically an SBR without a stock body. I can't shoulder or get a cheek weld on my Glock. I had the money and wanted a toy. It's still a free country for a little while longer anyway, so I can do as I please. True that...an AR pistol is BARELY a pistol That's why their so much fun and hated so viamently by the anti's. 
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Sure they will fragment. Will they penetrate? I have no idea if they will penetrate to a depth you want or in what media your talking about.... I doubt very seriously they would make the touted 12" in balistic gelatin since the hornady round won't do it out of a 16" brl and the remington round i used apeared to perform pretty much the same as the hornady in my very informal test. I'm also convince by looking at the informal testing i did with them i have no desire to be shot with one. 
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