Had a similar experience some years ago with a Glock 30. Handload with a medium load. Don't remember powder, probably Unique. Using Jacketed bullet. Blew out right side of magazine release and cracked the receiver. Fortunately I was shooting left handed. Sent the gun to Glock and they saved the slide. They put it back together for a reasonable price at the time. No accusations of "Double charge" I think a double charge would probably have done more damage. I was using brass that I had used in the past for other 45's. (1911 and 645). I don't know what age your 21 is but take a look at the feed ramp and see how much is unsupported. I don't have the 30 anymore but happily load some newer 19's. I have no interest in reloading for any factory barrel besides the 9mm in a Glock. These things happen and it isn't always operator error.