Carbine Vs Mid Lenght Gas System...

[UtopiaTexasG19]

Using two 16" Ar-15 rifles as examples where both are set up the same except one has a carbine lenght gas system and the other a mid lenght gas system what are the pro's and con's of one over the other? The reason I am asking is that every AR15 I have owned in 16" barrel has had a carbine lenght gas system and I have been offered a 16" mid lenght set up at a very reasonable price and I do not know what to expect from what I have shot in the past. Thanks...

[Quentin2]

Which brands are you talking about? If there's a wide quality gap that matters more than gas length. In general many of us prefer midlength for 16" and carbine length gas for 14.5".

You can expect a softer, smoother operating 16" rifle with mid gas.

[mxsailor803]

Def a smoother functioning out of a mid-length. I usually prefer a carbine though. All 4 of my uppers run carbine systems so if I ever want to swap parts around (probably not) its not a big deal.

[Palmetto-Pride]

Bayonet ends up in the correct spot with a 16" and mid length or a 14.5" and carbine length gas system........

[Theohazard]

The military M4 design is a carbine-length gas system with a 14.5" barrel. The civilian version keeps the same gas system length but extends the barrel to 16", adding 1 and 1/2 inches of dwell time and therefore more gas pressure. Most 16" barreled, carbine-length gas system AR-15s are over-gassed; at best an over-gassed rifle will have a sharper recoil and will violently throw brass. At worst, an over-gassed AR will attempt to extract the fired case while the bullet is still in the barrel and the case will be ripped from the chamber while it's still expanded against the chamber walls. This can cause everything from a little flash out of the ejection port to chewed-up brass and failures to extract.

A heavier buffer will fix the problems caused by an over-gassed carbine-length 16" barreled rifle, but a mid-length barrel lowers gas pressure and minimizes those problems to begin with. In my opinion, a mid-length gas system is a superior design for a 16" barrel 5.56 AR than a carbine-length system.

[RC20]

Good question and good answers

[Fishbed77]

Def a smoother functioning out of a mid-length.

Not necessarily true.

My Spikes M4LE carbine with an ST-T2 buffer and M-16 BCG runs as smooth as any rifle or midlength I've ever fired.

[Theohazard]

Not necessarily true.

My Spikes M4LE carbine with an ST-T2 buffer and M-16 BCG runs as smooth as any rifle or midlength I've ever fired.

Your carbine-length setup may be smoother than most mid-length setups, but if you made it a mid-length it would be even smoother (it might end up so smooth it ended up short-stroking, but that's a different issue.)

All other things being equal, a mid-length setup will always run smoother due to the slightly delayed unlocking and the lower peak gas pressure. Sure, there are other ways to achieve this smoothness (which is why your carbine-length is so smooth), but I prefer starting with less gas pressure to begin with instead of compensating for that higher pressure after the fact.

[velocette]

I have found that some rifles with rifle length gas systems will short stroke when using the faster rifle powders eg: N133. Not so the carbine length gas systems.

Roger