Over pressure ? Causes ?

[Rearlugs]

Punctured primers are usually just a combination of slightly over-long firing pin protrusion and ammunition with tin primers. Shooters may remember the South African PMP .303" that gave up to 40% pierced primers in some rifles!

There is nothing in the OP's description that indicates a headspace issue, or any other more serious problem.

[Gaz]

I have had this problem with S&B .303" ammunition, but not their .308". My own theory is they tend to load towards the hotter end of the spectrum - I haven't had problems with other factory ammunition down the same rifles.