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Mentolio · Veteran Member

I recently rebuilt one of my Crosman NPs, using a 400 grit flex hone in the air tube. While smooth (cocking and shot cycle) and powerful (good velocity over the chrony), my extreme spread numbers are lousy, compared to the "old set up." Is this common with an actual hone, or does it sound like I have a bad seal (it was new, properly lubed, and carefully installed...but I guess anything could happen)? Maybe some other cause? I have several hundred shots through it, and accuracy isn't bad, even out past thirty yards...it's just the numbers and accuracy used to be better (significantly, in some cases). I'm seeing extreme spreads in the 20-40 range, with pellets that used to be in the teens and even some in the single digits. I was using CP Ultra Mags from the brown box, but am pretty sure I got a lousy batch (fit is pretty loose and inconsistent in the breech). I did get better numbers from other pellets I've used in the past, but still nowhere near the low numbers I'm used to seeing with this gun. Any ideas?

AirGunEric · Site Admin

While I obviously can't speak to the quality of the hone job- it takes time for the seal and cylinder wall to mate- as you have apparently put hundreds of pellets through it with no change- it's possible the seal has gone bad (or couldn't form to match the wall profile due to some imperfection in the seal prior to the hone. The thing to always triple check is that nothing (i.e. metal flakes) got left behind in the tube after the hone, or the chances of damaging the seal go up significantly.

Mentolio · Veteran Member

I've had a few bad seals, but the velocity always suffered (it's averaging over 800 fps with CP Ultra Magnum 10.5s, 900s with 7.9s), hence my hesitation to break it down again. Thanx for the reply, I'll pull it apart and check it out.