I was just at the Range with my Mosin 91/59, was shooting some com bloc surplus ammo. I noticed the brass (about 5 of 15) had a crack or two down the neck all the way down to where the case expands, there was also a little chip missing right off of the front of the shells. I have shot mabey 5 shots out of this rifle before this, with that green steel cased stuff and it didn't crack those. Is there a problem with this rifle, or is it just the ammo? Is it unsafe to shoot like this? I would rather not blow myself up.
The link shows a head split, which is a bad thing. Your getting neck splits (in brass) which while not good, isn't all that bad either. The problem stems from improper (or no) annealing after the case was formed. IMHO shoot em.
When you go see him, take 3-6 fired cases (steel, brass, brass w/split) along with some unfired (steel and brass). Ask him what he thinks the problem is.
He may want to do a chamber cast, in addition to the headspace check, inorder to check the actual chamber dimentions.