First, try closeing the action with a little more authority. You shouldn't have to slam it....but a firm SNAP usually clears up alot of misfires. I still catch myself trying to ease it shut, especially when sitting in my tree stand on a quiet morning. If that doesn't work, I'd try blowing out the action with some compressed air making sure the air isn't full of moisture. Having the problem with two different barrels(especially when one is a .22 rimfire) leads me to believe it's not the barrel or locking lugs. That leaves the frame and you(technique). Tell us what's happening when you get a misfire. Are you getting any indenture on the primer at all?
And, I almost forgot, hammer extension?....can cause misfires....If you're using one try it without and see.
GOOD SHOOTIN', Walt