GTA
General Discussion To Gateway To Airguns => Gamo Gate => : daved February 12, 2007, 04:03:20 PM
-
After the disappointing showing yesterday, I got to thinking about the oring seal on the rotary breech. Anyone that specs these things will tell you that an oring really should be a static seal. However, if it's going to be used the way this one is, the sealing surface needs to be as smooth as possible. So I opened it up again, with the intent of polishing the area that the oring rides on.
The first thing I did was look over the rotary very carefully. And I noticed something I've never noticed before. The front face, where it seals to the barrel, looked like it had been hammering against the end of the barrel, instead of being cushioned by the seal. Seemed like the seal was too deep. So I used a peice of fine solder to shim it out. I also noticed the rear oring had a nick in it, so I replaced it (AGAIN!). There were also a few rough spots that I cleaned up with some 400 wet/dry.
After a thorough cleaning of the compression tube, I did a careful inspection of as much as I could see. First thing I saw was some scratches on the bottom of the tube, extending up to the breech area. The breech area itself looked to be honed to about the same level as the compression tube, which was what I expected. I chucked my hone into my drill, started with a 1" wide strip of 400 wet/dry, then worked my way up to 1500, just in the breech area. For the compression chamber, I worked it over again with the 400, but was more aggressive this time. I also checked the piston over thoroughly, I wanted to know where those scratches came from. There was a rough spot on the piston head, the rotating part where the seal goes. It also wasn't turning very freely. So I smoothed up the rough spot and freed up the piston head, and started putting it all back together.
At this point I parted from common practice. Instead of using moly and silicone to lube everything, I decided to use some teflon grease I had on hand. It's actually a lubricant for trailer hitch balls. I've had good luck with this stuff on almost anything. It works well, it lasts, and it doesn't seem to react to or with anything. Lubed up the rotary seals, the piston seal and piston trailing edge, and put it all back together.
First thing I noticed was that the rotary was much smoother and easier to operate. This is good, it was really stiff before, until I got a couple of shots off. Decided to run 10 heavies through first, have some 11.2 gr. Silver Arrows so that's what I used. The first shot sounded like a .22 LR, which will get your attention when you're shooting in a 10 ft. wide space! It also went about a 1/2" low. No more cracks, and the next 3 went through the same hole. Fired a couple more 10 shot strings with a couple of different pellets, was back to the sub 3/8" groups I was hoping for. Went ahead and chronied it again, much better results. Extreme spread for Superdomes and Exacts well below 20 fps, with SD back in the single digits. Velocity for the Superdomes averaged about 885 fps, Exacts were 835. Didn't have a chance to shoot at longer range, but I expect the results will be much better than last time. I still think the rotary breech is a serious weak point in the design of the CFX, but I think I might have finally figured out the solution. Hopefully, this will last, but I'll keep you all posted. Later.
Dave