Crosman 454 question

I just finished a reseal on this
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one. Was having the same feed issues. I polished the bb receiver. Sanded the plastic bb pusher. It still did the same thing. I noticed the bb's were snagging in the valve block, catching on the lip of the barrel. Backed out the barrel. .5 millimeters. Checked everything they now feed through. Put the gun back together. Still feeding bbs and shooting good after 300 shots.