DOug, I think you mean rifle upper with an M4 barrel extension ( like Bushmaster, RRA and many did for years). If you do rifle extension to M4 upper I can virtually guarantee constant stoppages due to the incompatibility.
Quote:
Originally Posted by AKDoug
There are plenty of people that claim it's perfectly ok to run a rifle upper with an M4 feedramp barrel. I've never done it, but I've seen a bunch that work just fine.