I had 2 MPX units, both problems with reliability, I sold them. I have 3 friends with an MPX, 2 sold them, 1 keeps on trying to make it work (all the time),
I shoot a JP15GMR now, as do my mentioned friends. Zero problems. Yes, some load development, we settled on wave spring, weight, blitz 5007 and 115's with VV N320. Done.
Since I am lazy about to buy a JP5 in order to shoot factory ammo without changing to many things. I love JP!