Hey all, anyone ever had this happen?
I have a preban essential arms lower, used to have a 20" M&A parts upper with bushy 20" barrel on it.  I just bought a bushy M-4 with A1 upper.  Using the same bolt carrier, bolt... this thing will simply not feed the right hand cartridge from a gi 20 or 30 round magazine.  This cartridge moves about 1/3 of an inch and stops the forward travel of the bolt.  Now if i pull the charging handle back and release, it will feed.  Thermolds work perfectly with no issues at all.  This is the same barrle that has fte with sa ammo.

Any thoughts guys?

Mortis...