I had to hammer the bolt open. What gives?

I thought we would make this a separate post.

I have seen this problem before and it is usually caused by
a) excessive case expansion
b) using cases that have been fire formed in a different rifle.
With the K31 and earler KAr11 signs of excessive pressure are not obvious. I would recommend that you compare the dimensions of your fired case with those of an UNFIRED new case (ideally a GP11 case or a Norma case). If you do not have virgin brass, then full length size a round..
I have a KAR 31 which shoots superbly but it's chamber is outside SAAMI spec in that a fired case looks like an "Ackley" with the shoulder blown forward. If I reload the brass more than twice by neck-sizing then I end up with tough extraction (especially with service velocity reloads).
If you have been using service ammunition or PRIVI Partisan ammunition and you are having this problem, then it is likely that your headspace is excessive.
Of course there is one last possibility and that is that although your reloaded rounds chamber, they do not chamber easily. If this is so, then you will end up with a mega extraction problem.
I have found that a good cure to sticky extraction with the K31 is to priodically re-size through a custom Redding body die for the 7.5 x 55 - I had a Redding bushing neck die and body die set made up 12 years ago. What a difference this made!
I hope that this may help. regards ... Anthony