17XX pistol build, tube issues PART II…
…I ended up taking an empty 12 gram co2 cart and put it in my drill chuck. I used bore polish and added sand to it. I opened it up a bit, but this still wasn’t enough. When looking inside the tube I noticed the hammer was still riding along the bottom. When I compared my other Crosman tubes I noticed a tiny space between the tube and the hammer where the hammer rode on the bottom. This is what I tried to duplicate with the DC tube. I used a round barrel drum sander on my dremel and took some steel out, then polished…and now the hammer rides as it should!
I spend some time before work trying different spring pre-loads and start pressures. I am using a heavier spring (not sure of origin…but it is heavier than a disco spring and three coils shorter). I am using 7.9 CP’s and shooting through a .177 LW 10.1″ barrel.
My first test I filled the tube to 3000 psi and ran a 35 shot string, however, the fill pressure was way too high for my hammer/spring and I started out in the 740’s and built up to 900 by the peak of the curve.
I kept the hammer preload maxed out but lowered the fill pressure to 2500 and I managed to get 15 good shots starting out at 878 and peaking at 904 and ending at 880 which gave me an ES of 26 for 15 shots, with an ending pressure of 1500. That’s okay for hunting, but I want to set this up to have more shots.
I tried backing the spring preload off 5 turns (same 2500psi fill pressure)and this proved way too much as my starting fps was way too low and I ended up with an ES of nearly 100 fps.
I put it in three turns so it was 2 turns out from max preload and I still was not happy with the ES. My starting fps was much better, but I still ended up with an ES of 45 by shot 15 so I abandoned the string.
Next I will try the spring preload in 1.5 turns to see what that does.After that I will try a different weight spring. I have a disco and a stock 2240 spring on hand.
As always, I am open to suggestions. I am going for a string of at least 25 shots (hopefully more) and an ES of 25 or better. Thanks.
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