Stevens 322a extraction

I've been shooting my 322a in .22 hornet a lot lately and an occasional problem has been creeping up.
The issue is related to the initial extraction. Every so often (maybe once in every 10-15 shots) the case will be extremely difficult to extract. The extracted cases look fine and the level of force needed to extract the stubborn ones varies from a stiff tug to a smack with a flash light on the bolt handle.
I happens with both my reloads and factory ammo, although less often with the reloads.
Any thoughts?

Sounds like the chamber needs a really good scrub. Try that first.