I am in the process of building an NFA/Class III short-barreled AR, and I plan on using an 11.5" barrel.  I have read that rifles with barrels this short sometimes experience cycling/feeding problems due to a lack of gas pressure.  If this is so, what is the easiest fix?  Or, will it depend on the indivisual rifle?

Hi Jason280... Hmmm... Well, I have a post-ban Bushmaster with an 11.5" barrel and an AK74 muzzle brake on it... It never fails to cycle or feed.  Works just as well as my pre-ban Colt.  

But of course the shorter barrel is probably not as accurate, and I can tell you IT IS LOUD!  Some of the noise might be from the AK74 brake.. it forces the gasses up, but mostly to each side... It's so loud that people come from all parts of our shooting range to see what I am shooting!  I like the 16" barrel myself, but hey, I am just a novice compared to some of these guys & gals on AR15.com.  [uzi]

Excellent thread here:

[url]http://www.ar15.com/forums/topic.html?id=55374[/url]

I don't understand the fascination with tiny pistol sized barrels....  

Here's my advice on the AR-15. I admit that I'm not the most fluent gun guy on the board, but when I got my AR-15 there was one thing I kept in mind.

Many people think that the AR15 shoots a pussy round. Lots of guys insist on the .30 cal theory, but the .223 is a potent round if it is used the way it works best. The .30 cal guns usually don't break the 3000 fps (feet per second) barrier. The rounds are usually heavy (The 7.62x39 weighs in at about 123 grains i think) and the bullets pack a lot of energy. One reason that the 7.62x39 is said to be so inefficient at killing is because it buzzes right through targets unless it impacts a solid (bone, skull, etc). The .223 is a fantastic round when the ballistics exceed the 3000 fps range. Once that sucker gets moving, the bullet becomes very deadly.

Think of it this way...... If I jump off a diving board into a pool I break the water and slide right in. Now, if I jump off a helicopter into a still body of water, the water does not break fast enough, and my bones will break. Now if I jump out of a satellite and hit the water (considering that I don't incinerate in the atmosphere) My body will explode as it enters the water. My body will burst into many pieces, and bits of my body will go shooting into the water in many different directions.

The .223 can burst after only a few inches of soft tissue. The round does not cut well through the flesh since it's going so fast, and it is not able to stay together. The bits of copper jacket fragment and zip through organs as the lead flattens out and then flies every which way as it bursts.

[b]Yowch[/b]

Now, the thing that's silly to me is the guys that insist on shorter and shorter barrels. Some dudes have 14" barrels with a 2" brake on it to meet the 16" bbl requirement. The preban guys will get these uppers that have shorter barrels than pistols! Well, the .223 coming out of these short barrels simply does not build up enough pressure to become effective. The tiny 55 grains of metal enter the body, and often does not even destabalize before it passes through the body. Seems to me that it completely negates the advantage you get with the round. In Black Hawk down, the spec ops guys were using the 11.5" bbl and repeatedly complained of the lack of effect the bullets had. The bullets hitting the somolies were compared to ice pick stab wounds. Very tiny holes that went right through. They were using tungsten tipped 62 grn rounds, but still the analogy would likely hold with the 55 grn rounds.

I went with the 20" barrel to keep my fps high. I don't think that cutting off 4" of barrel to have a little package will really ever make a lot of difference in manueverability. I also liked the Heavy barrel since it should aid in accuracy.

Well, that was my though process in getting my sexy momma....

[img]http://www.student.smsu.edu/s/srv656s/ar15right.jpg[/img]

Here is a diagram of the .223 at different velocities.

[img]http://www.gunsnet.net/forums/attachment.php?s=&postid=384533[/img]

Shawn

One more thing... notice that in the diagram, the round really began to explode when it moved at 3000 fps (about mach 3). This velocity is usually only acheived in 20"+ bbls. (correct me if I'm wrong)

I just think the short bbls sacrifice performance and are mainly used for looks....

Shawn

Ditto ARnSC comments, have a Bushmaster 11.5" w/5.5" FS and it runs perfectly.

Generally it's uppers shorter than 10" that experience the problems you have mentioned. I  have had experiences with shorter uppers and while I could tune them to run, switching lowers meant re-tuning it all over again, a real pain.

IMHO if you stick w/ a Bushmaster 11.5" you'll be very happy w/ the way it runs.

I also agree w/ ARnSC on the accuracy issue, while the cool factor of an SBR (NFA rules apply) is definately appealing, unless your a SWAT/LEO entry team member using it to do room clearing drills, groups at 100 yards will be considerably larger (1-1.5") than any 14.5" M4 or 16" barrel groupings.

Hope this helps,
Mike

srv656s...

Good post,  but I think that Jason280 was talking about the [u]reliability[/u] of 11.5" barreled gun, not the [u]effectiveness[/u] of .223 out of said gun.

Polishing the chamber usually resolves the majority of reliability issues in short barrel M16 pattern guns.