My firstthought, once I'd seen the "spent" primer in the pic was that he's somehow managed to "prime" the case with a previously fired primer. Hence, huge firing pin indentation, burnt primer composition, but "bullet no bangy".
I too was confused by that. Until I re-read carefully and realised that was a different 'photo, from
@Alantoo , showing what looks like a faulty primer that fizzled. I'm pretty sure that Alantoo made his cartridges well, and that his 'photo showed a (rare) faulty primer.
We still know nothing more about
@Andy seatrout s primer (or the 5 out of 30 that didn't go bang in his previous experiments).. If those have been preserved and could be photographed for us to examine, we might have something to discuss.
Meanwhile I'm wildly guessing that poor primer seating might be the root cause. And a dodgy box of primers the least likely.
Likewise what was his drill when the misfires occurred ? And how is he seating his primers, in his progressive press ?
These sorts of posts are interesting to me, but since I have never experienced anything like this myself, other than on a couple of occasions shooting ancient military surplus .303 Berdan primed stuff, which always did fire after a second attempt (just re-cock the Enfield No.4 by pulling back on the cocking piece, bolt kept closed throughout).
If it didn't fire on second strike (never happened to me but sometimes did to others), raise hand, RCO stepped over to observe and if necessary advise, rifle kept pointing downrange safely, wait at least 30 seconds before cautiously ejecting round.
Same principles should apply to sporting rifle usage, particularly if you are using a turnbolt that can't be re-cocked without opening the bolt. Other mechanisms are available to deal with this very rare (but not in the OP's case), scenario. A Sako 75 in fit condition (firing pin, spring, firing pin hole, clean inside, lightly lubricated, no trigger sear drag from misaligned safety catch, improperly adjusted trigger etc.) shouldn't have a problem firing a properly made reload, even with OTT headspace.
Until we have further "post mortem" info from the OP, including how he is going about making his rounds on his progressive press, we are all just speculating. But to be frank, if a reloader can't make ammunition that goes bang every time, there is something wrong with what they are doing. This is pretty fundamental, and may suggest that other aspects of their reloading procedure are also not as tight as they should be.