My upper has m4 cutouts, the barrel I am looking at does not. Will that be an issue?
Yes, because the barrel extension will slightly overhang the cutout in the upper receiver.
Combinations and problems are as follows:
No M4 uppper + no M4 barrel extension - no problem
M4 upper + M4 barrel extension - no problem
M4 upper + no M4 barrel extension - could be a problem
No M4 upper + M4 barrel extension - should be no problem
You'll have to contour the the barrel extension to line up with the M4 cutout in the upper to elimninate the extension 'overhang'.



























