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twalter · Veteran Member

After doing some extensive reading on tuning cheaper air rifles (mine in question happens to be a gamo hunter 220) I see there are some ways to create the tight fit desired to smooth out the firing cycle. I found quite a few articles about shimming the spring guide(with beer cans or shrink wrap) and top hat to create a tighter fit along with delrin strips or buttons to shim the piston carriage.

Im most curious about the nylon/delrin strips. Anyone have pictures of them doing this and have a source to buy/order them?

Also, has anyone else shimmed the top hat for a little more power or to allow the spring to turn more freely?

Slavia · Moderator

Shimming the guide is to dampen vibration. A steel coil spring increases in diameter slightly when it compresses. The guide should go into the relaxed spring with a bit of drag. When the gun fires, the spring moves freely because it has expanded away from the guide. At the end of the stroke it clamps down again, dampening vibration. I think Alstone of this forum did the metal shim variation once. Another approach is to machine a new, fitted guide. On my Slavia going to a stickier grease did the trick.

When compressed, the spring ends also rotate relative to each other. That's why people polish spring ends and add polished washers. If the spring ends can't spin freely, that twisting stress can get translated into the spring kinking (and then "strumming" on release). Personally, I would just go for smoothness and not extra power. If you do go for power, be careful that you don't add so much washer thickness that the coil binds before the sear can latch. Give it at least 1/4" of free space.

I have buttoned two guns, and it did make them smoother. I didn't trust glued-on plastic, so I went with metal. On my Mendoza RM577 I had a welding shop goober on some brazing rod, which I cut down for fit. On one of my B3's I soldered on buttons of pistol shell brass. Compression tubes aren't perfectly true, so you have to fit the buttons to prevent binding anywhere in the piston's travel.

Here are some glue-on buttons:
http://www.airrifleheadquarters.com/catalog/item/251488/2365157.htm

AirGunEric · Site Admin

If you look at all the tuning "kits" for springers in the market- they are all doing essentially what Slavia has noted- taking up more of the slack inside the spring and adding/replacing guides with polished washers and delrin (i.e. softer than steel to allow some flex/compression). The idea being, also as per Slavia- to smooth things out, not increase power (although some might increase power very very slightly- i.e. a couple of percent). The problem with most of these "kits" is that they are made for one version of a particular rifle and often need to be "customized" to fit correctly (i.e. not exactly "drop in") so you're better off saving the money and doing it yourself as you've suggested.

twalter · Veteran Member

Thanks for the replies.

I did order a E3650 and an R9 along with a new seal and buttons. I disassembled again took out the old spring that was bent and got to looking at what I have to work with. I do have a steel top hat that needed some dressing up to take off the burs and have the head seat flat. I also found that the maccari tar that I had put on the old spring had migrated up along the seal and it was what was robbing me of power. I dont think Ill used it again for dampening... Anyhow, I grabbed the 2 springs I received and decided to go with the shorter spring thinking it was the lighter one of the two. Well I think I got it wrong as I went back to the website and noticed that E3650 is a 35 coil and the R9 is a 32. Opps is all I can say. I have put about 100+ rounds through her at the moment and she barks like a NP. Short and sharp. I did add 3 nylon washers between the top hat and spring guide(my thinking was shorter spring...) and this seemed to work best between no washers and the 3. I also added a soda can shim to the top hat guide with a little moly and it helped to greatly smooth out the cycle. The spring really grabs the rear guide and dont think I can get a shim on there nor do I need it. On to the finished product; my shot cycle is rather smooth all things considered. It gives a nice solid thud, with little to no twang but I still have that very loud report. My former go to pellets dont group very well but my H&N 'cuda 10.34gr stack right on top of each other with the old gamo rockets(the rifles former first love) coming in a close second.

I think I going to install the other spring and see how things work out with it and report back with my findings. I find this all rather enjoyable.
I might add a little tar with the moly on the spring guides to act as a slight dampener.

Lastly, what do you all think of bumper washers(rubber washers) added inbetween the top hat and spring guide ? I was thinking one or two sandwiched in between the nylon washers, but I was also thinking it may give a slightly different compression as it ages giving inconsistency in the shot cycle. Im guessing its possible to add a little moly to them and change them out maybe every 6 months to a year if I get decent results in actually placing them in there?

Slavia · Moderator

A while back I used neoprene washers in a Crosman G1. It did reduce vibration. The ones between the top hat and piston head held up just fine, but the one on the rear spring guide disintegrated. On that gun I also cut back on the spring spacer, so the washers I added didn't increase spring loading.
http://www.airgunhome.com/agforum/viewtopic.php?p=15054&highlight=project#15054

twalter · Veteran Member

twalter · Veteran Member

Update from today...
This thing is shooting like a dream. It is smooth, incredibly quiet and accurate once again. There is almost no mechanical noise when cocking and with another 100 or so shots its a nice thud. With the piston shims, nylon washers and just enough tar around said items I have no twisting or jumping in the shot cycle. It is a straight forward and back. Here are a few shots from sighting in tonight.

6 shot group from tonight

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twalter · Veteran Member

The range Im testing her on. The rest is a block of 2x8 cut down with high density foam glued and then covered in gorillia glue real tree tape. I have a tripod 1/4-20 receiver in there for it to use a tripod shoe. Since Im using high rings and was not getting a consistent eye relief I had to use the foam and neoprene sleeve that used to reside on my shotgun.