I have 2 RimX actions , one has a Keystone bbl . one has a PVA bbl , I have interchanged both bbl's back and forth on the 2 actions , because I can ! 4 mags , 2 with the +5 ext. , 2 without , ZERO problems , 5/6 K on the PVA , Rock Creek bbl , probably 2/3 K on the Keystone , BenchMark bbl ...