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It can take a while before the penny drops with me sometimes...
I was prepping some once fired sako 243 brass a pal had given me. I tumbled them, full length sized them and cleaned the primer pockets. then they had sat in a tub for a bit.
The beauty of fora like this is they they give me an encouragement to get on with things.
Last week, i got the urge to prime them. I had a few Federal primers left, so thought I''ll use them up and get them shot before doing some more.
For some reason, it diodn't register in my thick head that it was hard seating the primers 'til I'd done 10. Then I realised it didn't feel right. I even had a couple that wouldn't seat. It was like they had military crimps.
I stopped, changed cases for some Federal ones. Easy - no probs.
I then tried some Remington primers in the sako brass. Great fit.

Is this a known issue with Federal primers and sako brass?

Are there other compatability issues that others have found?

I have not used Sako brass so in that respect I cannot answer however I had a vaguely similar problem 2-3 years ago. I started having problems with primers and .303 Winchester brass, what I did discover was my old and faithful Lee primer tool no longer liked .303 brass, swapping to a RCBS primer tool resolved the issue. Odd I thought but still have the Lee primer tool.

Had a similar problem with Norma cases many years ago. The problem is that there can be microscopic differences in primer sizes that make a particular make of primer incompatible with certain cases. The solution is simply to change the make of primer to one that fits that case.

Or use the Sinclair primer uniformer or similar to cut them to size.

EDIT - I have one here if you want to try it. Seems silly to scrap the brass or change primers.

The manufacturing tolerances can sometime work against each other when maximum size primers meet minimum size primer pockets then things can get a bit hard to seat. I find radiusing the primers pocket with a chamfer tool helps. I do this as standard practise when I case prep the batch the first time and this or primer pocket swaging is a must for any military crimped brass. However this and even enlarging small pockets with a uniformer can still leave large primers tight .

Using a priming system with greater leverage can also help as ovenpaa found when he switched from the lee to the RCBS. I have some PPu military primers that give very consistent SDs but are a bugger to seat and I have to use something with a bit of leverage like the Wamadet system, a press system or a press mounted Ram Prime, I like the Lyman unit best.

Sometimes you just have to try different batches of primers with different batches of cases to see what fits, fortunately it is not too common an issue.