GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: fivestar45 on February 17, 2015, 07:26:11 PM
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A while ago I started to get involved with a .22 cal 850. As I only shoot using co2 power, my aim was to make it as efficient, and powerful as I could using co2 only. So as usual I nickeled, and dimed my way through the project which had about a two year punchline.
I was hindered a bit along the way by a bad OEM barrel and a bad replacement barrel that Umarex U.S.A. shipped to me. So to start things this is what the second barrel looked like after disection.
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850bbldent.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850bbldent.jpg.html)
You will notice the dent in the ID at the back of the front sight screw hole.
After that cut I faced it on my lathe, and re-crowned it. Now that was one problem down.
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850bblcutoff.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850bblcutoff.jpg.html)
Next up was getting rid of the roll pin that holds the barrel to the receiver. I did that by indexing TDC of the barrel in the mill and milling three small flats to match up with three 8/36 grub screws that I drilled and tapped in the top of the receiver.
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850bblscrewflats.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850bblscrewflats.jpg.html)
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850recbblretain.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850recbblretain.jpg.html)
Also drilled and tapped for the front sight, and closed off the top port hole.
Barrel work done.
I was never crazy about the OEM sights so I re-worked a Williams WGRS 54 Peep to fit the 850's scope rails.
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850wrgspeep.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850wrgspeep.jpg.html)
And added the fiber optic front sight from a QB78 deluxe that I had in my parts bin.
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850frontsight2.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850frontsight2.jpg.html)
Now on to another personal peeve, the bolt handle. I just didn'nt like the big OEM handle. That one was easy. I turned and polished a St/St shaft and planted a Brass Ball on it. Done.
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850bolthandle.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850bolthandle.jpg.html)
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850rtreceiver.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850rtreceiver.jpg.html)
I started out bulk filling the Factory 2x12g adapter from the valve end
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/8502x12grefill.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/8502x12grefill.jpg.html)
After a while I got bored with removing it to refill it and decided to make a new cap that was long enough to show through the fore stock and added a Forster fitting with check valve. All Good, now it can be
filled, or topped off without removing it from the gun.
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/8502x12FrontFillampOEM.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/8502x12FrontFillampOEM.jpg.html)
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850BulkFill2x12FrontFill.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850BulkFill2x12FrontFill.jpg.html)
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850FrontFill-1.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850FrontFill-1.jpg.html)
Now onto the power plant (valve). Since I only intend to use co2 for power I initially figured that I'd follow Raold's lead. I eliminated the screen under the piercing pin, and drilled three supplemental feed holes around the perimeter of the pin.
The next area I wanted to improve was the stem and seat. The OEM parts do a good job of sealing but I thought that they required a lot of striker spring to make things work especially in warmer weather. I felt the key here was a smaller diameter seat and a harder seal material than the OEM O ring. So off to the lathe to turn up a new brass valve top with a raised seat that finished up a few thou over 9/32" dia. and opened up the bore a bit to 1/4". Now the stem. I used a pc. of drill rod and turned a Red Turcite head.
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850ValveStem1.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850ValveStem1.jpg.html)
This combo wouldn't give me a dependable seal at co2 pressures. So on to try another stem, this time White Delrin. My results in the past with this material have yielded a reliable co2 seal.
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850ValveStem2.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850ValveStem2.jpg.html)
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850ValveStem2a.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850ValveStem2a.jpg.html)
Bingo! A reliable seal. However, when chrony testing this valve using a stock striker and spring I'd get 50-60fps drops from the first shot (about 720fps) and each shot there after.
So I decided to try two modifications which I would usually do one at a time in order to evaluate their impact. Mod #1 I reduced the striker weight from 59g to 53g I did this by opening the spring bore and turning a Delrin insert to bring the I.D. back to size. And lastly,#2 a lighter than OEM spring, a Crosman part that I had on hand. The results...better than I'd hoped for. Now remember, this is co2 power and a short barrel about 74deg'sF.
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/ChronySheet.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/ChronySheet.jpg.html)
After this I energized myself to scratch build a larger 1" OD cot tube from 2024 Aluminum.
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850alumtube-1.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850alumtube-1.jpg.html)
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850LongTube.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850LongTube.jpg.html)
After some Duracoat.
The Finished Product
(http://i494.photobucket.com/albums/rr305/rainmaker20/Hammerli%20850/850rt-1.jpg) (http://s494.photobucket.com/user/rainmaker20/media/Hammerli%20850/850rt-1.jpg.html)
I hope this experiment helps some of you folks. Even though it was a bit time consuming it shows that with a little re-doing more power can be gotten from these guns when running on co2 without the need for a heavy striker spring,and striker or shorter shot count. Most likely this valve combination will give similar results when running the 850 on bottled air.
Have Fun
Anthony
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Wow! Interested in an 850. That is my next gun. Very nice job!!