Hey guys. Been having some omgoing issues with a 111 338 win mag. When i first got it i had light primer strikes, but after i started neck sizing. this went away, except for a rare exception. so with the neck sizing i have been shooting some older 4064 powder, imr. with 230 eld bullets. these bullets seat very deep to stay clear of lands. I got up to 64 grains but had presseure signs with primers. so worked back down to 62,7 grains. Still had leaky primer, and a cracked case head above the belt on another one. So i poured powder out on paper to look for rust, but powder looks good. There is some rust spots on inside of can. Metal can. blue can. so decided to start over with once fired and some new brass. and i full lenght resized about 15 rounds same bullet and seat, at 60.1 grains. third shot total case head separation and collapsed shoulder. i checked the head spacing before with blue tape for shims on the case head. but i didnt take the extractor out. So it probrably wasnt accurate..measurement. i am thinking either powder or head spacing?? what you guys think? Full lenght brass gives me issues, but could also be old powder. any thoughts?? Should i take extractor off and try to check head space again ???. some guys use aluminum can shims also. Not sure what is giong on but it sucks...i got the separated case out by the way. been reloading 41 years and never had to deal with this