AR reliability/barrel length correlation?

[Vapor Trail]

I've read over and over that the shorter you go, the less reliable the gas system is. That's why people almost always make their 7-9" rifles piston setups. Does that mean that a 20" barrel is inherently more reliable than a shorter one? I know that it's not the barrel, it's the gas length, but IMHO it's easier to compare with barrel lengths.

[ra2bach]

it's hard to make a blanket statement. I wouldn't necessarily say it's an issue with barrel length as much as it is with dwell time associated with how much barrel is past the gas port as well as the size of the gas port and buffering and spring issues.

the system was designed around a 20" barrel with rifle GP location, receiver extension, buffer and spring. moving to a collapsing stock changed the second part of that equation.

looking at it solely as a dwell issue, a 16" midlength maintains the same amount of dwell as a 20" rifle, as does a 14.5" carbine with appropriate GP sizes. SBRs use the carbine gas but open up the GP to deal with shorter dwell and reduced gas flow.

buffers weights and spring rates can be juggled to achieve the best performance within those parameters...

[Clint]

dwell is one aspect, but "delay" is another critical piece.

Delay is the amount of time from firing to start of extraction.

IMO, more is better.

There are three components of delay.

The gas port location is the first component we'll call "port delay".

The AR DI gas tube creates an additional "gas delay".

The cam pin's cam track form the "mechanical delay".

Combining the three provides the total delay.


Piston guns generally only have port and mechanical delay.

PROPER piston guns have gobs of mechanical delay. e.g. AK, SCAR

[brzusa.1911]

I currently have 16" middy and 14.5" middy - both 100% reliable.

[lethal dose]

The number you're looking for is a 36" barrel and a custom 28" gas tube. Combine this with a .025" gas port and you'll rock and roll all day (assuming you have the custom gas block, too). Why? Because, at that length, all the gasses burn up and enter the gas tube and because it is so long, the gasses actually freeze causing the inside of the gas tube to freeze and become very slick. This, in turn, "hypercharges" the gas resulting in extremely high reliability and a very cool running system. :cool:

[justin_247]

With an auto carrier, as long as the gas port is between about 50-70% of the length down the barrel and is properly sized along with the correct buffer, the weapon should run reliably.

[Iraqgunz]

Vapor,

You need to read more and post less.

[lifebreath]

Catagory 7: "It All Depends."