340E 222 Sticky bolt

Gentlemen, thank you for having me. I tried using the forum search option first but to no avail. I have a 340E .222 used/new to me, first time I shot it recently. I cleaned the bore and chamber prior. I shot about 10 rds of PPU 50gr sp (came with it). The bolt became difficult to open after firing(not so before hand or when cycling empty. What might this be indicative of? Oh yes, also I had just put about 100 rounds thru a Mini-30, everything was grand. 10 rds of 222 made my shoulder sore. My old neighbor shot it, said it felt like a 30-30.

I'd try some different ammo. I shot some PPU .22 Hornet in my Savage Sporter and had the same problem, and some pierced primers. That stuff may be a little hot!