Marginal aspects of AR design.

[Outlaw Man]

ARs have habituated people to the idea that rifle bolts break. But other rifles don't break their bolts. Barring overloads or other extreme abuse AKs, Garands, M1 Carbines, and M1As all typically run their bolts until the receiver is worn out

Which is cheaper and easier to replace: a Garand receiver or an AR-15 bolt?

Designing the weapon to fail in a controlled, predictable manner after a moderate (10,000-15,000+) round count rather than a significant (and potentially catastrophic) failure sounds like good, not marginal, engineering.

Would you rather have to replace your engine and still have a pretty much brand new car after 100,000 miles, or would you rather have an engine that runs forever and have to start swapping car frames?

Sure, through some design changes and 21st Century metallurgy, you could have an AR-15 built like an Abrams tank. But who, including the US Government, is going to want to pay $3000-4000 per rifle in exchange for not keeping a couple spare $150 bolts/BCGs around?

 

[Slamfire]

XTRANX is putting chamber flutes in their versions of the AR15. It is my opinion that chamber flutes should be in all gas guns, whether they are delayed blowback or not. They have to be in the HK roller bolt delayed blowback mechanisms or those actions would rip the case in half. Delayed blowback actions unlock early compared to other actions and friction between the case and chamber is so high, that the mechanisms require lubrication of some sort. Prior to chamber flutes delayed blowback mechanisms required either greased cases, (such as the Oerlikon 20mm anti aircraft gun used by the Navy from WW2 up to Vietnam http://hnsa.org/doc/gun20mm/part4.htm page 105
) or oilers, which lots of nations used, or gas lubrication, which has displaced all the oilers and grease.









For almost one hundred years, gunwriters have been spreading ignorance by claiming that friction between the case and chamber is necessary, in fact claiming the gun will blow up if it is removed. But in the real world, increasing friction between the case and chamber causes failures to extract. This lie started almost 100 years ago as part of the coverup of the blowups of the 1 million single heat treat 03 receivers the US Army built and gunwriters, not having the education or sense to know different, have been repeating it ever since.

Breaking the friction between case and chamber increases extraction reliability. You want the case to fall out of the chamber. If the extractor has to mechanically rip it out of the chamber, sometimes the case stays. I really doubt there is anyone who has fired more than just a box of ammunition has not experienced a failure to extract. Or had to get a cleaning rod to knock a round out of the chamber.

XTRANX has created shallow spiral flutes for their barrels. This is a step in the right direction.

 

[sawdeanz]

Everything in a design is a compromise. In the case of the AR many compromises were made to make the gun light, accurate, controllable, and reasonable in manufacturing costs..
The buyer / user needs to understand the realities of service life, have realistic expectations, and replace components, or even the whole gun periodically.

I second this and am thankful that there are many designs to choose from.

I also second goon's question. I too thought I read that one expects a carbine length gas system to impart undue wear compared to what is was originally designed for. Can anyone validate this?

Lastly I myself am wondering whether competing designs like the SCAR, Robinson Arms XCR, Bushmaster/magpul masada thing etc. which share similar bolt designs and mechanism have addressed these design aspects or if theyjust carry them over in a new package.

 

[tahunua001]

this is quite interesting.
I've had short strokes with an AK, 10/22, and marlin 60. haven't put much rounds downrange in my SKS but I'm sure that I could have issues with it if I used crappy enough ammo. I have yet to get short strokes with either my 5.56 or 9mm ARs and I've accidentally put 380 through the 9mm before. not saying that short strokes don't happen but the AR is not the only semi that has problems with it.

bolt not strong enough? there are fellows that go 100,000 rounds through their ARs before replacing anything and the barrel is usually first to go, not the bolt. you have sources that show damaged or broken bolts being prevelent in the ar15 or are you citing a single thread on arfcom where a guy with a blackthorn kit had issues?

extractors not being strong enough I'll concede to you there. I've seen a x39 AR snap the extractor after less than 100 rounds of steel cased through it but in all fairness it was a blackthorn kit and there was much more wrong with the rifle that had to be replaced before it even began to resemble a decent build. stronger extractors are not hard to come by and do not remove any modularity in the least.

debris mitigation is kindof overblown. I've been lugging my AR15s with no forward assists or dustcovers around the backwoods of idaho which includes rain, snow, dust storms(albiet not sand storms) and being banged off trees and dropped in mud. I have never had a failure in the field and doubt I ever would. keep it clean and it will run.

there is a reason that the M16 has been the main battle rifle of the US armed longer than any other design. the closest contender than I'm aware of(since muzzle loader days) is the springfield 1903 that lasted from 1903 to 1936, around 2/3 the time that the stoner rifle has served. the design has also been updated in bits and pieces over the years and some people ruin it by slapping pistons and rails on it(my opinion, please don't read too far into it) but for the most part I think the AR is a very good design.

 

[MCMXI]

Showing photos of broken bolts is pointless without information regarding the gas system, round count, ammunition used etc. Not all ARs are built right.

 

[Robert]

Ok, I am going to call this one. If someone can produce citation as to where any of this has been a major issue then I will review it. And no a Hesse, or Blackthorn or whatever they go by now does not count. They are crap from the word go.