midlength

[bobo1972]

lokking to build another ar but would like to do a midlength. I dont know to much about them though. Is it the length of the barrel or how far the front sight sits more forward that makes it a midlength?
also can i still buy a barrel shorter than 16 inches?
Any help would be greatly appreciated.
if anyone could post a pic it would be good to so I have a point of reference.

Thx James.

 

[cancer]

Buying a <16" barrel won't be a problem. There's quite a few used ones on the EE. If you want new though, you'll likely have to contact Dlask, as they're the only Canadian manufacturer of AR parts.

 

[P0WERWAGON]

most midlengths are 16, but there are some 18 SPR setups. the midlength is from the position of the gas block on the barrel.

 

[recce]

If you're going for a 16" barrel the mid-lenght looks better in my opinion.

Kevin B posted some data a while back that shows that 16" is a very sensible length and helps to eliminate some of the problems with gas issues in the 14.5 and less barrels and is close enough to the velocity and accuracy of the 20" not make no big difference.

 

[furet]

The mid-length refers to the gas system length.

Some dimensions, receiver to gas block (ie, ~handguard length / gas system length)

- Short (CAR) = 7.5"
- Mid-length = 9"
- Rifle length = 12"

Then there are the pistol types which use other non-standard sizes.

2 dimensions to consider when selecting barrel:
- The gas system length. The longer the gas system the smoother the bolt operation.
- The distance from the gas port to muzzle, this plays a role in the reliability.

The original design is built around a 20" barrel with a rifle gas system, which gives you about 6" from gas port to muzzle.
Having a shorter post gas port length can create cycling issues.
These 3 configurations are the only ones that follow that characteristic:
14.5" with short gas
16" with mid-length gas
20" with rifle gas

Some general barrel configurations:

10", 11.5", 14.5" use short gas systems.
16" use short or mid-length
18", 20" use rifle length

I have also seen 14.5" with a mid-length gas system.
Other non-standard combinations might exist also.

 

[Hungry]

Hey furet, thanks for that technical post.

Powerwagon: thanks for the comparison pictures.

All this is helpful information to the newer black rifle addicts.