I'm pretty sure this is a field I'm well-versed in, and whilst this is somewhat illegal, I strongly oppose these laws.
But yes, you are using rimfire .22 rounds right, and striking them off-centre? The last thing you need is to add to the already fairly high misfire rates in .22 rounds. How's it feed, have you got an ejector lip in there or do you shake the brass out? If you're using pine in the chamber, you're probably going to get splintering, regardless of the support given by the plastic piping, I'd strongly suggest using a metal breech if you can get one.
Also, where the forget is the trigger, god damn open that stuff up so I can see how you made it.