Which design is more reliable?

We shall define reliable as follows:
       Less prone to malfunction and jam, given EXACTLY equal circumstances and the same type of ammo, and mags. (ex..failure to extract or eject, rip through case rim, etc etc)
       Less likely to break parts, and the one less likely to wear out parts faster than the other (if there is a difference).
       All in all, which one will last longer, given equal amounts of usage and the PROPER maintenance and care.
   
   This includes BOTH semi-auto and FULL-auto applications.

   Some people say Stoner originally designed the weapon as a 20" because it was more reliable that way.

   Some people say barrels 16 inches and less send back a gas pulse too early which causes the bolt to extract the case before the case has had time to shrink back to a "normal" size.  Which, in turn, causes extraction problems.  Which is why we have things like smaller gas ports, different kinds of gas tubes, and the midlength upper.

   Some people say the shorter buffer in the collapsible stock is less reliable than the longer buffer in the full sized fixed stock.

  These are things I have HEARD people say.  I DO NOT know what the "real deal" is, and would like to be enlightened.

   I am NOT worried about the length of the total weapon, or the weight, in the comparison.  It is not important to me in this instance.  If a 20" HBAR is the most reliable (due to both functionality and lower barrel temperature when fired for long periods full-auto) so be it.  If the weapon weighs 15 pounds, that's ok.  I will get my fat-ass in the gym until I can hustle with it.

   Thank you VERY much everyone,
     
      Stainless

I really don't think the barrel length or the shorter buffer in the collapsible stock has any effect on reliablity.  If a shorter barrel and buffer reduced the reliabilty to undesirable levels the U.S. special forces would not use M4s.

The critical dimension appears to be the length of barrel from the gas port to the muzzle. This distance determines how long the gas operates under pressure on the bolt/carrier. The 14.5" barrel is reliable because it has the same length of barrel in front of the gas port as the 20" (which means it will  take a bayonet as well). Barrel lengths below 14.5" are less reliable, though with work-arounds like longer gas tubes or different buffers, they can be made to work.

A 16" barrel has even more barrel length from gas port to muzzle, and I've never heard any reliability issues endemic to the 16" set-up.

I have noticed no difference in relibility between the 20" and 16" AR, or any reliability difference in the type of stock.  I have found that the main reliability issues from the AR stem from the bolt assembly, like broken extractors, weak extractor spring, lack of lubrication/cleaning or broken firing pin.

Any one else have any ideas?

All other things being equal, the 20" rifle will be more reliable because the AR was designed as a 20" rifle from the start.

Shortening the barrel to 16" causes increased gas pressure and faster cycling but you are still using components designed for the 20" system.

Is it a dramatic difference in reliability? Not really for most of us, but start adding heavy firing schedules and suppressors and you'll notice the difference soon enough.

Uh, no, there was a down range velocity/range requirement imposed on the original design posed by the helmet penetration. Using the ammunition of the time a 16" barrel wouldn't have made the grade.

Have I mentioned this really great book called, [b][i]The Black Rifle[/i][/b]?
[img]http://www.collectorgrade.com/shop/media/blackrifle.jpeg[/img]
I have? Odd, you would think more people would have read it.

Given your definition of reliability (esp the parts wear issue) the 20" is more "reliable".