12.5" barrel on a mid-length gas system???

[myv6]

So basically I've got a BCM 16" mid-length upper and CMR 12" rail that's not being used.

Is there any reason why it would not function if I chopped the barrel to 12.5?

[GH41]

So basically I've got a BCM 16" mid-length upper and CMR 12" rail that's not being used.

Is there any reason why it would not function if I chopped the barrel to 12.5?

Only one reason.

[myv6]

Only one reason.

Thanks, very helpful.

[GH41]

Thanks, very helpful.

I am glad I could help.

[Shiz]

Dwell time. After your projectile passes by the gas port, until it leaves the barrel it is pushing gasses into the gas tube and BCG/piston. Really basically, if there isn't enough dwell time, then it doesn't push hard enough.

Best gas system for a 11.5 or 12.5 is carbine.

[Grip]

So a midlength 13.7" barrel has enough dwell time? 1.2" is the difference between working and not working?

Im just curious.

[PD Sgt.]

You may want to look up "dwell time". A midlength gas system on a 12.5 does not allow enough gas to get back to cycle the weapon reliably before the pressure drops as the bullet exits the barrel. Even some 14.5 middys can be finicky with lower powered ammo.

ETA I was beaten to the explanation.

[dentron]

If you are going to get your barrel chopped, why don't you just have adco do it and they can relocate the gas port too.

[mig1nc]

Is this going to be for a dedicated suppressor build? Just wondering. That changes things a bit.

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[MegademiC]

So a midlength 13.7" barrel has enough dwell time? 1.2" is the difference between working and not working?

Im just curious.

Sort of. You can always open up the gas port until it works. People run 16" rifle-lengths, but I would advise against it. There is little forgiveness from a reliability standpoint.