[venture]

Question for the GBBR doctors here. I have just acquired a KJ M4 and am starting the learning process.

Can an M4 GBBR in general, and the KJ TK designed M4A1 in particular, accommodate a 20 inch inner barrel? Can you even get one for a GBBR that long?

I am thinking about cylinder porting in aegs to prevent too much air blowing out the barrel. Are GBBR's calibrated to barrel length this way? Basically I would like to make an SPR or M16 out of it.