I have a new 6.5 Grendel upper that is rifle length gas system. I have a carbine length buffer tube and a mid length gas .223 upper.

If I can't get ahead on selling the 6.5 Grendel pistol can I run a rifle length or vltor A5 length buffer assembly and switch the uppers.

I have it on good authority that even with an adjustable gas block the upper won't cycle with the carbine length buffer

I'm not 100% sure on the grendel, but you can absolutely use a rifle length gas .223 upper with a carbine length buffer tube. I can't think of a reason a properly functioning upper with an adjustable gas block would not work.

My carbine buffer weight/spring will not cycle the rifle length 6.5 Grendel even with the adjustable block.

The gun will fire
The bolt will cycle and eject
The bolt will not lock open on an empty mag or pick up a new shell

I've never had any issues swapping different length uppers with different lowers.

Fishin Texas Aggie 05 said:

---

My carbine buffer weight/spring will not cycle the rifle length 6.5 Grendel even with the adjustable block.

The gun will fire
The bolt will cycle and eject
The bolt will not lock open on an empty mag or pick up a new shell

---

Have you checkwd to see if the gas port is large enough? Looked at a weaker apring to allow the BCG to go all the way back to pick up the new round?

JP Silent capture system may work as well.

https://www.rainierarms.com/rainier-arms-ultramatch-mod2-6-5-grendel-750-gas-block-fully-fluted-barrel-18/

This is my barrel