20" Uupper on an M4 lower...

[AMMOTECH]

20" Uupper on an M4 lower... I've got a 20" BM upper that I'm looking to run on my M4 stocked lower. Anyone doing this? Any issues with the shorter buffer tube/ lighter buffer when doing this?
The upper came from the factory with that lower ( I swapped the stocks) and I'd still like to be able to use it. No need for it sit and gather dust.

[Robb Jensen]

99% of the time this combo works just fine. Just be sure to use a CAR weight (2.9oz) buffer, if you use heavier ones you'll be more likely to have short stoking. With really weak ammo you may have some function problems too.

[Parabellum9x19mm]

what about rifle buffer tubes with 16 & 14 inch barrels?

[Chris_C]

what about rifle buffer tubes with 16 & 14 inch barrels?

I have a CA lower with a RRA upper, heavy 16" bbl with an ACE full length skelton stock.

Runs perfect. No issues.

I also have a 20" with 6 pos stock. Runs fine.

[AMMOTECH]

I've ran a 16" on a rifle buffer with no problems; just never done it the other way around.

When I'm able to get to the range again I'll check it out. I'm going to run the 20" on different lower (Wife's BM) as my dedicated M4 lower has an "H" buffer and I'm to lazy to swap it out. ;)