9mm AR buffer plus buffer spacer?

[kylednf]

Finished my 9mm AR and was wondering about my build. I haven't shot it yet.
I have a YHM 9mm buffer running in a carbine length buffer tube. I also bought a buffer spacer as I read this helps the reliability and wear.
I was wondering if the buffer spacer is necessary since I am using a 9mm buffer or does the added length make up for it? Should I not run both at the same time?
-Kyle

[Jon Road King]

The more you reduce the momentum of the BCG as it slams over the bolt release, the less likely it will break the bolt release. You can do this by adding weight (heavier buffer), or reducing the travel of the BCG (spacer). Or both. Most folks recommend both - so running with a spacer AND the heavier buffer is ideal.

Pull the bolt back and observe where it is, in relation to the bolt release. If your bolt face is still set back by an excessive space, you can just drop quarters in the bottom of the buffer tube (in addition to your spacer) to further reduce the travel of the bolt if you need to. But my guess is, with the spacer you already have, you should be OK.

However, I am not sure what length your spacer is, but if your BCG clears the bolt release (locks open), as assembled with your YHM buffer, then you should be ok.

I set mine to clear the bolt release by about 1/4" (with just quarters - no spacer) and it runs like a champ. But 9mm AR's are fickle, and not all run the same, so take some quarters to the range and adjust yours as necessary if you need to.

[ar15barrels]

Finished my 9mm AR and was wondering about my build. I haven't shot it yet.
I have a YHM 9mm buffer running in a carbine length buffer tube. I also bought a buffer spacer as I read this helps the reliability and wear.
I was wondering if the buffer spacer is necessary since I am using a 9mm buffer or does the added length make up for it? Should I not run both at the same time?
-Kyle

You need 3/16" to 1/4" of extra bolt travel BEHIND the bolt stop for the next cartridge in the magazine to pop up by the time the bolt is on it's way forward to feed it into the chamber.
Anything MORE than 1/4" extra bolt travel is going to beat up the bolt stop when the bolt stop is activated by an empty magazine.
If the spacer and 9mm buffer combined give you just 3/16" to 1/4" extra travel behind the bolt stop, you are good.
If you don't have 3/16" extra travel, shorten the spacer accordingly.

[Munny$hot]

Exactly what AR15barrels said. You should have a 1/4" clearance at full retraction behind the bolt catch with the YHM buffer since it's longer than a standard buffer. If not using quarters as shims behind the recoil spring will allow you to adjust the bolt and catch distance at full retraction.