Why couldn't i leave well enough alone?

[josh3rd]

Today I'm down in the basement... hold on for a second everybody isn't that where everything bad happens in the movies? In the basement. As far as I know nothing good ever comes from being in the basement which leads me to my story. Okay I'm down in the basement and I wanted to check how my soda can piston sleeve was doing. FYI to those who would like to know, so far so good. No scratching, no aluminum bits and pieces in the tube. And it is still keeping the "spring twang" down. Well last night I was talking to a gentleman who was very informative and knowledgeable in airguns especially springers. While I was picking his brain he told me about how easy the piston should slide down in the compression tube by its own weight and if you hold your finger over the transfer port hole you can hold the compression tube up and the piston will not fall out.

Okay so I tried it and it did not slide down the tube whatsoever without me giving it some help. So therefore I tried to resize the seal with some 400 grit sandpaper. It seemed like I was doing that forever because the it did not slide down by its own weight.

So here's the idiotic part. I decided to use a Dremel and take some material off the seal but idiot me took way too much. How much is way too much? It'll slide in the compression tube as fast as gravity will allow. Man I am so mad and upset with myself. I put the rifle back together and proceeded to see how bad the damage is. Funny thing is is that it's still grouping pretty good for 10 shots but there is a very noticeable difference in Recoil now. I hope I have enough bullseye bucks to get a seal from Pyramyd Air.

For those who may know what I'm going through, will it mess up the rifle if I continue to shoot it? I do not have a crony so I can not tell if it's shooting fast or slow or good or bad aside from what I have already told you. Thanks to all of you for being the shoulder to cry on at this time.

[Hsing-ee]

Air will leak past the undersize piston seal and cause the piston to slam into the end of the cylinder. Depending on how robust the cylinder and piston are it might cause no damage or it might start mushrooming the piston head or causing problems at the junction between the end of the cylinder and the transfer port block. Power will be reduced. I would stop shooting the rifle.

The 'dropping under gravity' thing is not really necessary. If you can move the piston with finger pressure, that is fine.

Get a new seal, if it is a very tight fit then perhaps take a little off it by spinning the piston in a drill and taking a little off the edge of the seal. If it isn't very tight then I suggest shooting two tins of pellets (1000) through the rifle in a couple of massive plinking sessions and that should size it to the cylinder.

While you are waiting for the seal to turn up, strip the rifle and try this basic tune ...

http://www.airgunbbs.com/showthread....ing-Gun-Tuning

Just curious, how did you use a Dremel to do the piston seal sizing? The dremel chuck is way too small to fit a piston rod inside it. You can't have gone around the outside of the seal by hand with a small sanding drum because that would make the seal out-of-round almost immediately.

[TonyL]

As above.

[Shed tuner]

The 'dropping under gravity' thing is not really necessary. If you can move the piston with finger pressure, that is fine.

Yup. In fact I much prefer the shot cycle of springer when there is a little more drag on the piston - less bounce, and a softer final piston landing.

The gravity thing is really if you are trying to wring every last smite of energy out of a gun, and even then, it's easy to go too far and sart losing seal.

Finally, when resizing seals, I have always found that once sized, they initialy wear in (i.e. wear down) very quickly before stabilising, so if you do need to size a seal, always size it a bit over, then shoot say 50 shots through it. You'll be surprised how much the resistance reduces in thsis short time..

[TonyL]

Again, top advice from JB.