Shaving a sliver of lead off the bullet is obviously due to there being a sharp edge along the bullet feed path, somewhere. The fact that it's semi-circular and ends up on the bench and not IN the mag suggests it's happening after it leaves the magazine, but before it's chambered (Likely the feed ramp? I forget what they look like on the 10/22). That narrows it down to a fairly small area... Might have to do some disassembly, but I'm sure you (Or your gunsmith, depending on how mechanically competent you are. No offense intended, you either are or aren't) will find a sharp edge that wasn't deburred after machining. A few quick passes with the right needle file should clear things up.