I was just looking at that download you linked to, and I noticed that under Magazine springs it didn't list them by weight but it did mention the number of coils. I'm assuming then that he took the stock glock 19 springs with 9 coils put in glock 17 springs with 10 coils. When the pistol is fired, could the strong springs be forcing the next round up on its way into the chamber before the extractor extracts the previous round?
Again, I know nothing about this stuff. Just a guess so please don't be afraid to tell me I'm an idiot.