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 Post subject: Re: Is This Fixable?
PostPosted: Tue Jul 17, 2018 9:53 pm 

Joined: Fri Jan 25, 2013 9:51 pm
Posts: 257
Location: Dryden, Ontario
Daryl wrote:
Appear to have dressed off the breech - re-cut the seal groove and likely set the barrel back using a bushing in the pivot hole.
That's my guess.

Actually those are the three things he mentioned.When I was dremelling the hole sometimes it would slip and run right across the face of the breech.Happened a few times.It was a funny though at the time.Live and learn. :D

 Post subject: Re: Is This Fixable?
PostPosted: Tue Jul 17, 2018 10:30 pm 

Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1271
Location: United States
I'm guessing he sanded it down? Good thing you had lots of droop or it wooda been a much bigger pita. Whatever the case it came out great, the droop is gone, nice rubber O-ring and same day service! Good job MyCrosman.

pelsby: In the pix below you can see the breech is often very sharp since cheap guns cheap out on everything, especially machine work. The pells skirt is larger than the bore and meant to swage down as it goes in, plus the air pressure is very high so it doesn't just push it straight in, but outward as well. With the edge in the pix it'll literally shave off lead like a potato peeler. This is bad for the pellet and the next pell that will hit any lead slivers left behind. Basically you just wanna little bevel, or what I prefer is a little radius b/c even a bevel has an edge. I have a 45 degree countersink tool to break that edge, which I do gently by hand. Then I use very fine sandpaper to turn that into a more gentle radius. With that super low seal the OP had I rekon the breech may have also been pinching the skirt. Something to consider depending on your breech and pellet choice. I like JSB pells which have a very thin skirt so easily pushed in enough, but pells like a Crosman Premier with a thick skirt may stick out too far and get pinched. You just have to check it and decide if it needs fixin, if so do you want to force the pell in deep enough ea time (pita) or make a deeper bevel. I think for most a switch to JSB would fix it, or at least need less bevel.
The bigger the bevel the more it hurts performance, like the OPs 30fps loss which is a lot in ftlbs. The air gap between the barrel block and breech hurts it too so try to keep it as small as possible.
The below pix is of a Crosman NPSS which is not the same model as the OP's, but while different I'm pretty sure it's also made in china. Usually they make some varying effort to bevel it but as you can see that step is often skipped. The crown is also something to look at b/c they're even worse at doing those. Imo all that's really important is it's 90 degrees to the bore so when the pells skirt exits it's perfectly all at once. If uneven then the exiting air blast and friction is uneven at that moment which will no doubt upset the pellet. Springers have very little blast but many people claim a fixed crown made a big diff.

Breech bevel.jpg
Breech bevel.jpg [ 110.85 KiB | Viewed 150 times ]
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