9mm AR Upper

[Super Dave]

It keeps the bolt from traveling as far back, and increases the spring pressure on the bolt. Remember, this is blow back operated. The spring pressure and weight of the bolt/buffer is all that is behind that little brass cup when it goes boom, as opposed to the locking bolt of a 5.56 that is moved by gas pressure after the projectile has passed a port in the barrel.

 

[BigDiezel]

Also helps prevent breaking bolt catches.

 

[Super Dave]

To shoot the 9mm upper what do I have to do to my lower?
I'd like to build just the upper

From my sniper hide

Also helps prevent breaking bolt catches.

That too!

 

[Shadowrider]

I'm just in the process of building mine so bear that in mind, but here is what I think I've learned.

1) hagn block is tits.
2) I'm building a pistol with the Sig TAC brace so I went with the KAK gen 2 pistol tube. It's made to use std carbine length buffers and spring no spacers or custom buffers.
3) very heavy buffer and Wolff extra power spring makes them run smoother. (So I've heard and I'm going with a 9mm buffer. They are the same as a carbine buffer just much heavier, like 5.7oz IIRC). Remember, the BCG and buffer spring are what holds it in battery until the bullet leaves the barrel, so making everything "stiff" supposedly helps smooth it all out.
4) I'm running a YHM ramped BCG with a standard CMMG LPK, so we'll see how it works out.


I'll post up any issues I run into and if I'm off base anybody please feel free to correct me. I learning too.

 

[Shadowrider]

Superdave beat me to it with the blowback thing.

I've heard of guys using a stack of quarters for a spacer too.

 

[Super Dave]

I'm just in the process of building mine so bear that in mind, but here is what I think I've learned.

1) hagn block is tits.
2) I'm building a pistol with the Sig TAC brace so I went with the KAK gen 2 pistol tube. It's made to use std carbine length buffers and spring no spacers or custom buffers.
3) very heavy buffer and Wolff extra power spring makes them run smoother. (So I've heard and I'm going with a 9mm buffer. They are the same as a carbine buffer just much heavier, like 5.7oz IIRC). Remember, the BCG and buffer spring are what holds it in battery until the bullet leaves the barrel, so making everything "stiff" supposedly helps smooth it all out.
4) I'm running a YHM ramped BCG with a standard CMMG LPK, so we'll see how it works out.


I'll post up any issues I run into and if I'm off base anybody please feel free to correct me. I learning too.

Sounds good! There are many ways to skin a cat!

 

[Jedabug92]

Odd question. Could the spacer go between the spring and bolt?

From my sniper hide

 

[Super Dave]

No.



....

 

[Jedabug92]

No.



....

Would a heavier buffer weight work?

From my sniper hide

 

[GUN DOG]

what did you make your spacer out of and how long. I'm running complete cmmg dedicated lower and upper. Got them seperate few years apart using their buffer and spring. May have to stiffen it up after reading this. I usually shoot home cast lead boolits