GTA
General Discussion To Gateway To Airguns => China Gate => : shady816 April 05, 2010, 12:44:31 PM
-
I took some time out today to sit at the work bench for a good while and thought I might have a look under the hood just to see everything and make a few measurements. I did take a few photo's of the works. and a HUGE THANKS to Willie aka speedturtle if it had not been for your short lesson on the breaking down of this gun I would not of been so confident. now after breaking the gun down entirely, I took a look at the seal and would luck have it, it was roughed up pretty bad around the outside with small bits missing around the edge (looked like a very small squirrel chewed on it) and also is there not supposed to be at least some lube on it, take a look at the photo of the parts on the bench I barely got my hands dirty pulling it apart it seemed very dry only the cooking shoe slot showed positive signs of lube,i have some apex seals so I went ahead and honed and debured the entire thing and installed new seal and went with the original spring which showed no sign of issues and reassembled the entire gun and off to the range. it took about 50-75 pellets and it was shooting pretty good ,better than before but not exactly perfect but I will say if it can hang in there right were she's at now it will be my choice gun for this weeks 30 yard bench rest. I intend on changing the spring and new guides soon.
-
Nice spring compressor rig you got there, shady816. From the looks of your stock piston seal I'd say it's really a bad one. Glad you have some apex seal to work with. With my B26 I am using the Crosman quest piston seal which is quite similar in fit and size to the stock BAM B26 piston seal. The only issue with it is that it's too hard. If you got the time you can actually "button" the piston unit for a good fit to the compression tube. That would help it shoot smoother. Happy to be of service to a fellow airgunner, Sir. :)
-
yes thank you again the spring compressor rigs a bunch of scrap I had around. as for buttoning the seals this is terminology I have yet to learn I am learning one step at a time. thou I did fit the new seal it was a little tight so I made a mock piston end to chuck in the lathe to use to resize a seal, worked great. as for the gun it still has allot of twang but the recoil died down I think the lack of compression in the last seal caused excessive piston slam causing unneeded recoil.
-
Piston buttoning is more like preventing too much tolerance between the O.D. of the piston unit in relation to the I.D. of the compression tube. Subtract the O.D. of the piston unit to the I.D. of the tube and divided it by 2 will give you a fair idea as to how thick your button material should be. I don't have the JM button materials so I just made my own from a nylon washer and sand it down to get the right thickness that I need. To attach it to the piston unit body you have to sand the part where the buttons will be glued. It has to be totally clean and devoid of any lube to make a very good gluing surface. You can use the ordinary blue loctite super glue. Just a drop is more than enough for each button. To position them ( I suggest about 3 pieces to the rear of the piston unit) position them at exactly 12 o'clock, 4 o'clock, and 8 o'clock if you are looking at the piston unit from the rear. if you have a good fit on the piston seal you might not need anymore buttons at the front. Test you airgun with the rear buttons first and if it works smoothly then don't put any buttons at the front anymore.
On my B26 I was able to greatly reduce the spring twang by using a custom delrin top hat. IMO the B26 system doesn't like to have a very front heavy piston system so adding some thrust washers or a steel top hat does not help a lot. It makes the recoil too harsh causing the B26 to literally jump on your palm during the firing cycle. Unless you want power before accuracy then you can take this path and do it. With me I'd rather shoot a lame airgun but puts the pellet at the same spot than a powerful one but can't hit the side of the barn. If you want to further play around with your B26 you might want to try using a softer piston spring or shorten the stock one by about 5 - 8 turns. This will give you a ball park velocity of about 800 FPS which is a very nice velocity between 15 to 45 yards of shooting distances using pellets in between 7.9 to 8.4 grains.
-
Nice job Robert. Soon, airgunners will be coming to you for advice. Interesting spring compressor.
Speedturtle is a wealth of information and he doesn't mind sharing with the airgun community. Thanks ST.
Happy shooting.
-
Just returning the favor, Sir. I just learned these stuff from fellow airgunners like the folks we have here and at other airgun forums as well.