Odd tightbore experience

Wait... So you're hitting human sized targets at OVER 350 feet, but are inexperienced at gun work? Sounds fishy...

Also, it seems like there's something wrong with the nub, or bucking. Did you clean it out weird, or so something funny when you put it back together?

No, just "sprayed silicon oil on it". He did this so it doesn't rip, but it's hurts the performance. I would either re-do it, or either shoot and shoot and shoot until it wears down, but that doesn't always work. Take it apart and wipe it down. Just remember:

NO OIL ON INSIDE! This is where it touches the bb! The outside is ok.

By the way, the bucking is the thin rubber sleeve, if you didn't know.

Yeah, that seems very far. You must have did a ton of work to get your gun like that? What's your internals look like, and what are you shooting at?

Well, I'm impressed with your tech if these numbers are true. If you are shooting uphill, at a target that is higher than your elevation of your rifle, then the distance would increase. I could see it shooting 400 feet on flat ground, but that is remarkable. How big's the target? Good accuracy either way though! Nice job!