I'd guess the 6.5 started to slow down and tumble while the 50 just punched right through it.
Shoot a regular sized 80 page magazine with a .22lr and a 9mm. The results will be the same. The 22 will have a large exit hole because it's "slowly" tearing through the last half of the pages, and the 9mm is still trucking along and produces a nice clean hole.
|