Interesting read on barrel lengths

[DanVoils]

AR-15 Rifle Barrel Length - Does It Even Matter? Maybe NOT

Dan

 

[SSGSAD]

AR-15 Rifle Barrel Length - Does It Even Matter? Maybe NOT

Dan

GOOD Read ..... I still like my 20" .....

 

[DanVoils]

GOOD Read ..... I still like my 20" .....

Thanks. Same here on the 20" but it's a stainless bull barrel and weighs about as much as one of my truck tires. Maybe an exaggeration but probably not by much. It is a Rock River LAR15 that I wish was threaded.

 

[MrAverage]

Also enjoyed the article, guess I can't blame my accuracy on my 16" barrel.....I'll have to rely on cheap ammo as a more educated excuse.

 

[KJQ6945]

Good read Dan, I would be interested to see more testing. Why did Crane decide on 18" with the MK12, etc.

Thanks for posting.

 

[Mgderf]

Interesting read.
Didn't Eugene Stoner originally design it with a 20" barrel?

 

[2in1evtime]

This was a very interesting read,, thanks for posting!!!!

 

[cop car]

It's all about everything working together. Barrel type, twist rate, length, projectile weight and powder load. When people build rifles they don't sit down and road map it all out. Before you buy anything you need to decide you want to do with it. Also, when you shoot it, need to always be using the same ammo. I know of quite a few people that have "good ammo" set back for when things go bad, but when they go shooting it's wolf or pmc that they are shooting. Which is fine, just make sure that your sighting in with the ammo you are going to shoot, and to shoot it so you know how the rifle behaves.

 

[canterbc]

Trying to decide the shortest barrel length for an AR pistol I will be building. I've been told don't go below 10.5" but I really want as short as possible, around 7". I wish the short barrel in the article was 5.56 not .300BO.

 

[cop car]

Trying to decide the shortest barrel length for an AR pistol I will be building. I've been told don't go below 10.5" but I really want as short as possible, around 7". I wish the short barrel in the article was 5.56 not .300BO.

Anything under 14.5 makes 5.56 a flame thrower. 10.5 with a can is iffy. Lots and lots of unburnt powder and pressures. Personally on 5.56 I wouldn't go shorter than 14.5. If you want shorter go 300 blk and go as short as 6.

 

[KJQ6945]

10.3" will work fine when done right. In my opinion, the 10" guns get a bad reputation from people building them and using the wrong combination of parts. My factory built gun runs flawlessly, whether suppressed or not.

 

[avboiler11]

I've got a 10.5" 5.56; it has run 100% with an A2 FH, a flash can, and a SiCo Omega...with everything from Wolf steel 55gr to M193 and Mk262.

The difference in 10.5" and 7.5" 5.56 is a LOT more muzzle blast and corresponding substantial drop in velocity, along with a pistol gas length...making it a less desirable combination. If I wanted a sub-10.5", I would absolutely choose 300BLK.

 

[Leo]

That was a pretty interesting article. I was curious about the same thing and did an experiement.

I had built a 26 inch barreled AR flat top. Since I used an aperature match sight at the end of the barrel, the extended sight radius DID truly give an accuracy advantage, especially at the 600 yard prone target. That length of barrel also requires a relocated gas port or the timing/pressure will give problems. All my loads were basically a case full of Varget under a 77 gr Sierra. More powder was never an option as the case was already full. Lighter bullets were a compressed powder charge of Varget.

The surprising thing was that velocity was not significantly higher than a 20 inch barrel, at least with that ammo.

When time came to change that barrel, I took a chrono and a saw to the range with me. I started sawing an inch off the barrel at a time and shooting 5 shots over the chrono each time. From 26 inches to 25 to 24 was no discernible difference in velocity. From 24 to 23 to 22 was a small drop, maybe 10 or 12 fps average, 22 to 21 to 20 was loosing about 30 fps each time, as was 19 down to 18. At 17 velocity dropped close to 100 more, and I stopped the test partially because I was up against my gas port, but mostly I had found my answer. Since I was using the same barrel with the same chamber over the same chrono on a singe day, those variables were eliminated.

At least for the burn rate of Varget with a heavy bullet, after 21 or 22 inches you really do not gain velocity, like the article said, there is a point that friction overcomes the expanding gas. When the powder is fully burned, that is the end of the benefit.

The long sight radius was the only benefit of that 26 inch barrel. A person with a 20 or 22 inch barrel could employ a sight extension tube clamped on the barrel like used in small bore shooting and gain the same advantage. A person using magnified optics of some sort would not benefit from the longer barrel.

A standard A2 rifle gives up sight radius needed for distance accuracy. There was a competitor in Richmond that abandoned the standard sight on a standard A2 and used a clamp on sight riser at the end of the barrel, adding another 25 or so percent of sight radius. He did very well with it as the 20 inch barrel really gave up very little velocity.

Comparing the article and my experiment, we can also postulate that lighter bullets using faster powder would be more tolerant of shorter barrel lengths. Varget is admittedly a little slow for a .223, but it is very consistent, something target shooters demand.

 

[cop car]

10.3" will work fine when done right. In my opinion, the 10" guns get a bad reputation from people building them and using the wrong combination of parts. My factory built gun runs flawlessly, whether suppressed or not.

It's just a lot of pressure for a can to deal with. Anything under 14.5 really starts putting a lot of wear and pressure into the can, rather than the barrel because of the unburnt powder.

 

[avboiler11]

While shorter barrels will increase wear on a suppressor...most 5.56 cans are rated and warrantied for 10" barrels.

 

[70R]

Very informative. I'm still learning, so articles like this help. Thanks!