Shortening 6920 to 12.5

[Mr. Goodtimes]

I've always been a fan of the GL/SSC and 12.5 inch barrel guns in general. For several reasons Im going to be using a Colt 6920. I'm going to send the barrel to Marvin Pitts for cutting and also shaving of the FSB (unless I can score a 6920 OEM). The gun will be shot unsuppressed as well as suppressed and needs to be 100% reliable. The rifle will only be fed NATO pressure ammo... this being the case should I request Mr. Pitts open the port to any specific diameter or should the factory port work?


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[opngrnd]

What is GL/SSC? I'm interested in the exact same conversion to 12.5" sbr.

[sig1473]

What is GL/SSC?

https://www.m4carbine.net/showthread...rmation-Thread

[Mr. Goodtimes]

What is GL/SSC? I'm interested in the exact same conversion to 12.5" sbr.

Grenade Launcher Sound Suppressor Compatible. It was a standard M4 cut to 12.5 in and fitted with a rail which DD made specifically for the rifle. The 12.5 in length retained the grenade launcher step on the barrel.

It's also been said that a limited number were done up with KAC URX II mid length rails. Someone else may know more than me but to the best of my knowledge there is no evidence of the rifle ever being used in the wild, but rather a really great concept that fizzled.

I'm interested in doing the project with a mid length URX 4. I want to cut the barrel as it's cheaper than buying a new one and it also retains the factory Colt barrel.


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[JG007]

I've always been a fan of the GL/SSC and 12.5 inch barrel guns in general. For several reasons Im going to be using a Colt 6920. I'm going to send the barrel to Marvin Pitts for cutting and also shaving of the FSB (unless I can score a 6920 OEM). The gun will be shot unsuppressed as well as suppressed and needs to be 100% reliable. The rifle will only be fed NATO pressure ammo... this being the case should I request Mr. Pitts open the port to any specific diameter or should the factory port work?


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leave it to him, he will take care of it

just let him know if you will be using an H buffer, etc or he may verify function with a carbine buffer

[tom12.7]

Why would you care about needing the M203 notch on a rail that covers that?
A 12.5" 5.56 carbine gas AR can work well with a .065" gas port. That allows you to step up and down with buffer masses suited to that use.
Also remember that ALL NATO 5.56 ammunition is NOT equal at all. You can end up with a very wide variance, depending on ammo selection. Much of the import ammo is lacking in at least a few areas.

[Pappabear]

Why would you care about needing the M203 notch on a rail that covers that?
A 12.5" 5.56 carbine gas AR can work well with a .065" gas port. That allows you to step up and down with buffer masses suited to that use.
Also remember that ALL NATO 5.56 ammunition is NOT equal at all. You can end up with a very wide variance, depending on ammo selection. Much of the import ammo is lacking in at least a few areas.

Are you saying a 6920 barrel could be cut down to 12.5 and run well if suppressed? Or what would you consider the perfect length barrel to cut a 6920 WITHOUT modifying the port.

PB

[tom12.7]

A Colt like 12.5" 5.56 DI AR can run well with a H2ish buffer with a .065" port, ammunition depending for many.

[Mr. Goodtimes]

Why would you care about needing the M203 notch on a rail that covers that?
A 12.5" 5.56 carbine gas AR can work well with a .065" gas port. That allows you to step up and down with buffer masses suited to that use.
Also remember that ALL NATO 5.56 ammunition is NOT equal at all. You can end up with a very wide variance, depending on ammo selection. Much of the import ammo is lacking in at least a few areas.

Tom, I don't care about the notch. I just care about keeping the factory barrel. I was just explaining to another poster what a GL/SSC was.

EDIT: I also understand that NATO pressure ammo can vary, I just threw that in there to paint a picture that the gun didn't need to run on Wolfe/Tula, PMC Bronze etc...


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[pezboy]

FWIW, Crane spec on 12.5" (actually closer to 12.3") GL/SSC barrels was a .066" gas port. I'm cutting a barrel to 12.5" and will be going with a .067" gas port since that is a standard size.