Hold the phone my esteemed Jocko.
....MV and pressure are not intertwined. You can have two different factory rounds (same bullet weight) leaving the barrel at the same speed with different pressure characteristics. Pressure is a factor of the choice of powder (slower burning powders are more "forgiving" all things being equal), amount of powder, amount of crimp, diameter of the bullet, seating depth, even the choice of primer. An extra grain or two of Bullseye for example could cause a dangerous pressure spike, depending on the caliber and with the tiny .380 there is not a large margin for error. Then there is always the possibility of a bad lot of ammunition (that's why I asked him for the lot number) - bad powder, incorrect charge, contamination, poorly mixed etc. all these things can happen. Reloaders are all too familiar with the factors that can make a difference between a safe round and one that is going to create problems. Going back to Bullseye, the difference beween the suggested starting load (w/ a 95 grain bullet) and the maximum load is only .3 grains. That shows you how little it takes to experience potentially dangerous pressures (ref: Speer Reloading Manual #14). There is also the possibiilty that metal/stress fatigue (with the gun itself) contributed to the kaboom though I seriously doubt it but I just want to illustrate how may variables could be involved. Rather than speculate further, let's see what additional information surfaces. For starters, I'd like to see photos and the lot number has to be called in to Magtech.
As for the side plate in the P380 you may be getting an extra margin of safety over other pocket .380s. It's possible that the Magtech +P round that caused the kaboom in the LCP would have simply blown the side plate out with less damage to th the gun. The pressure has to go somewhere and the side plate is a path of least resistence. With BB ammo, only the tiniest section of the side plate in my gun came out of alignment - top right corner, no big deal. And yes, Kahr indicated to me that hot loads could do this. A couple of rounds of BB was all it took in my case.