ar barrels


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Bezoar
February 11, 2008, 09:05 PM
is there any HUGE significant difference between barrel lengths as far as accuracy go? Or is there any HUGE difference between barrel types, ie standard military versus bull barrels or "slim profile" barrels with recessed target crowns?

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Omnivore
February 11, 2008, 09:59 PM
Barrel length, in and of itself, has little to no effect on accuracy. Barrel quality does. Barrel length effects velocity. More barrel, more room to accelerate = more velocity.

Heavier barrels have a tendency to move around less during firing, and to change point of impact less when they heat up, than lighter barrels, so, all else being equal, a heavy barrel is considered more accurate. If you're firing occasional shots, i.e. the barrel cools down between shots, the issue of heat response is moot. My kid's lightweight Ruger M77 sporter shoots sub MOA when slow-fired.

A recessed crown is protected from inadvertent dings, and therefore protects the crown from deformation should you be so careless as to bump the muzzle against a hard surface. A target crown is produced with special care and provides an extremely square and true release point for the bullet, therefore allowing the bullet to fly straighter from shot to shot, or so is the current wisdom.

The only HUGE differences will be from a damaged crown, a damaged or worn-out barrel, poor ammo or, most importantly, the difference from one marksman to another. Almost all firearms shoot better than their owners.

HUGE is of course a matter of opinion. Some people would consider a 1/2 MOA difference to be HUGE, while others would never notice.

Update: I'll ad that a flash supressor makes for a superior "recessed crown" in that the entire muzzle end of the barrel is protected. I refer to a flash supressor (or a brake) as a "muzzle protector" first and foremost.

Update#2: Since you mention military barrels; our military has specifications that must be met before a shipment of rifles is accepted. I don't know what they are today, but during military production of the M-14 the "rack grade" rifles had to be capable of placing 5 rounds withing an area a little over 6 inches in diameter at 100 yards using standard military ammo. This would be considered dismal accuracy by today's standards, but it was good enough to take a communist out of a fight. Understand that many of these same rifles would be capable of much better accuracy-- this was simply the minimum performance standard. And since you mention barrel weight; the military "Match" grade M-14 had all the same dimentions as the standard, rack-grade M-14 (same barrel weight and profile). The difference was that the tolerances (the acceptable dimensional variations) were cut in half. It was simply made to higher standards.

The bottom line is that it is not the particular features that matter so much in the end, but rather it is the quality. Sometimes even then it takes a deal of experimentation to find the right combination of rifle and ammo, and shooter, to get the best performance.

brian923
February 11, 2008, 11:15 PM
good quality 16" barrels will keep up with good quality 20" and 24" barrels. maybe not out to the same yardage, but they can very much hold there own out to 500 yards. thats impressive.

Bezoar
February 11, 2008, 11:46 PM
Im new to the world of hte ar so im at a huge disadvantage.

What barrel profile/length works best at range with the standard flip rear sight such as DPMS sells?

DnPRK
February 12, 2008, 12:44 AM
Im new to the world of hte ar so im at a huge disadvantage.

What barrel profile/length works best at range with the standard flip rear sight such as DPMS sells?Most people find a longer sight radius (the distance between front and rear sight) allows them to shoot smaller groups. A 16" carbine has a sight radius of about 15" while a 20" rifle has a sight radius of about 19". That additional 4" of sight radius decreases aiming error. It also helps to get a narrow front sight post. With lots of practice, either sight radius will work. The answer to your question is either 16" or 20" barrels will work fine with either the Midwest Industries or Mangonel rear flip up sight sold by DPMS.

Another factor in favor of a 20" barrel is elimination of feeding problems. The AR-15 is gas operated. The gas that cycles the action is tapped off the barrel at the front sight base. The closer the distance between the chamber and the front sight base, the higher the gas pressure and more potential for violent action cycling (technical term is "over gassed"). An over gassed carbine can cause failures to extract (empty case left in the chamber) and can jam the carbine. 20" barrels don't have nearly as many jamming issues as short barreled carbines.

My advice to new AR shooters is to start with a 20" rifle with flat top receiver so you can mount optics. Once you become familiar with the traits of the AR, you can purchase a carbine upper half if you desire.

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