I've talked at length with Bevin about his BP's. He's called the mag master for a reason; he figured out a long time ago all the intricacies about the 2011 double stack mags and how to make them work reliably and with the extra capacity most want.
It's critical the bottom of the tube is within spec (size) just like the middle of the tube and the top of the tube (feed lips). If the bottom of the tube is too wide, and you install the u-pin into the BP and it's really tough to push in the BP will inevitably crack when the mag hits the ground. That extra friction of the u-pin fit creates a lot more stress on the material he uses to make the BP's. If the u-pin slides in when the BP is on the tube just as easy as when the BP is off the tube, the tube is within spec. When fitting correctly the BP then acts more like a shock absorber when the mag hits the ground, taking the majority of the impact, putting less stress on the tube itself, keeping all those other dimensions about the tube within spec. Aluminum BP's, giving the impression of being stronger because they are metal don't absorb all that impact energy, instead transfers that energy through the tube, which will more negatively affect al those critical dimensions.
Yes, he will replace cracked BP's, he's good that way, but when you contact him about it he will ask how the u-pin fit in the BP when on the tube.