Do I have a problem with my Nitro Venom?

[Giant bubble guy]

Hi everyone,

I am in the process of tuning my Nitro Venom .22. I've got it apart and notice the the area that the breech seal mates with has very course machining marks on it. Is that normal? Should I carefully file the marks away and polish the surface? This is my first "serious" air rifle and I feel very fortunate to have found this knowledgeable group. I've attempted to post a picture, not sure if it'll work. Thanks for any input.

Dustin 

[robtmc]

Personally, I would not risk a file in there, not sure I could ensure total flatness.

What I would and did do was wrap some 600 grit paper around a flat file and smooth the surface without removing much metal.  Just knocking the high points off the Chinese machining work.

Had to do this to the breech and barrel of my Trail NP.  They now show a very nice lockup wear pattern.

[Stickstoff]

Another option might be to get some Bondo 907 Glazing & Spot Putty and use that to fill the low areas and then do the sanding afterward to smooth the surface. That should get you pretty level. HOWEVER I'm assuming that once it's thoroughly dry and set the paint/putty would be okay to have in that location, ie no detonation risk. I've used it and my guess it that after 24 hours it would be pretty inert.

Before you do anything though, have you done any testing to see if you have a leak there? No problem means no solution needed.

[Giant bubble guy]

Thanks guys. You both have some good ideas. I guess I'll put it back together and see if it's leaking before doing anything else. The seal has the imprint of the machining marks in it when I load a pellet. I suppose it conforms pretty well. I'll post my findings after I put it all back together.

[Paul68]

You can polish it up with some fine grit as mentioned, otherwise do nothing. Keeping the surface flat and even is more important than the final finish as the o-rings are typically soft enough to contour to the minor machining imperfections. Polishing it a bit might help with seal wear.

[Giant bubble guy]

So far my tune consists of: installed a GRT-3 trigger, ground and polished the crown, chamfered and polished the breech, deburred every part of the action as recommended, honed the cylinder, installed a new piston seal from Air Rifle Headquarters, and cleaned everything. I bought the brass washers and ram bushing from airguntoys.com and will install them when I reassemble the rifle. I've run into a problem though: the bushing doesn't fit. It fits over the end of the ram just fine, but it won't fit inside the piston. I have a drill press and a mini lathe, so I can reduce its' diameter if I have to. I would like to know that I'm trying to install it properly first. I assume that it's supposed to be installed so that it covers the end of the ram? I found some pretty bad wear on the ram body. I've put 200 to 300 pellets through the rifle and it seems to me that if it continues to wear at the rate it has been that my ram will be ruined quickly. I also noticed some wear on the piston and action. I've included some pictures of the wear. I'm I being to critical? Is this normal wear?

Thanks again for all of the input.

[benj397]

Well, the bushing I received was too big too (Trail NP).  Someone said that you had to debur and hone inside the piston.  I made sure it was deburred, polished it and then honed it.  Still wouldn't fit.  So I put it on a dowel, spun it in my drill and using very fine sand paper made it smaller.  When I was finished, there wasn't any excessive play and it slid smoothly into the piston.  Be sure to lube the inside of the piston and the bushing.

In case your wondering about the lube, I used Krytox 205 on everything.

Oh, I etched the inside of the bushing with 280 grit and the end of the ram (black part) before glueing together so the glue would have something to grab.

[Giant bubble guy]

Well, the bushing I received was too big too (Trail NP).  Someone said that you had to debur and hone inside the piston.  I made sure it was deburred, polished it and then honed it.  Still wouldn't fit.  So I put it on a dowel, spun it in my drill and using very fine sand paper made it smaller.  When I was finished, there wasn't any excessive play and it slid smoothly into the piston.  Be sure to lube the inside of the piston and the bushing.

In case your wondering about the lube, I used Krytox 205 on everything.

Oh, I etched the inside of the bushing with 280 grit and the end of the ram (black part) before glueing together so the glue would have something to grab.

Thanks, I followed your lead with a twist. My piston was choked at the open end. I sanded the bushing to fit the larger part of the piston interior, then sanded the choked part of the piston end so that the bushing would fit inside. I hope that all of this attention I'm giving this air gun pays off. There was a grinding sound when putting the barrel back into place during cocking. I think it may have been the sound of the piston being scraped by something.

[benj397]

Yeah, I had taken extra care to to open the "chocked" end of the piston.  I don't know if I removed all of the choke or not but I did a lot of sanding on that edge.  Once I felt that I had removed most/all of the choke, I sanded the bushing down test fitting along the way.  The bushing slid nicely in when I was done and there wasn't any excessive wiggle room.  I inserted just the bushing when I was done to feel the smoothness and wiggle capacity 2 - 3 inches in the piston before installing it on the ram.

I've shot over 200 pellets since the mods to try to break it in some.  Tomorrow I plan on chronying and checking groupings with a dozen or so different pellets.  I do know that the cocking stroke feels smoother. I don't have any chrony results prior to the upgrade.  I do know it didn't shoot CPHP's and another brand of pellet well (don't have the can handy).  Oh, I mounted my new scope on it today.  A leapers 4-16X44 SWAT.

[aidave]

bondo is a horrible idea -- unpainted bondo absorbs water... unless they changed their formula...

[Stickstoff]

bondo is a horrible idea -- unpainted bondo absorbs water... unless they changed their formula...

It isn't Bondo, it's glazing putty or paint. Basically a toothpaste consistency primer you can use to fill scratches in paint without having to sand and fill a large area. The same stuff is sold under numerous brand names.

It could absorb water though, I'm not sure about that so good point there.