I purchased a used M77/22, first 2 shots:

Went online to : triggershims .com bought a few shims (.003" worked best for mine), I haven't shot it yet, but everyone says this will fix issue. Will update in next week when I get out to try it.
This was factory Hornady. The one on right actually split the case open. Please use caution, and eye protection of course!
**UPDATE**
After shim install, the groups may have tightened...but same results. Slight ring expansion at base, and one partial head separation as pictured above.
Guess it's time to send to a Smith... If I get my hands on some different factory loads, will try first.
If the OP comes to a solution, please recommend.
*2017-01-16 Hornady is replacing my ammo, see post #11.