Helping hand from the CO2 gurus if you please. I have some ideas about what is going on, but really would like some other co2 shooter’s thoughts..
Had bought gun running in the normal way, max. valve work, all the “tweaks, but has been tuned down from it’s 790 fps max to a sedate 650 fps (with 7.8gr. pellets) and made into a carbine Part of the tune-down was a lightened hammer and a nice restocking (thanks James).
Was getting a solid 60-65 shots per fill up (running on 12gr.). using light weight 7 and 7.2gr.) pellets that tend to extend shot count a tiny bit.
Got to thinking about the spring/hammer set up. Decided to try a SHORTER but stronger hammer spring. Short enough that there is NO contact with the hammer when the hammer contacts the valve. Feels weird, as you first pull back the bolt feel no tension at all for about 1/8â€, then the short-strong hammer spring engages.
Fooled around with spacers it until it was shooting to the same 650 fps level and gave it a run at 20 yards using the same light weight Hobby pellets.
Shot count went up to 85 shots before a measurable vel. letdown (was shooting groups and chronographing at the same time).
Same vel...same pellets...but the shot count goes up from 65 shots before letdown to 85 shots. I admit, as the shot count got longer, it took a longer wait for the temperature stabilization, but by shot #85, no matter how long i waited, was going to shoot slower than average. Same procedure for the first tests where 60-66 650 fps shots were all that I could drain out of a pair of 12gr.
Yeah..before you tell me...those Hobby pellets are not the best choice for consistent groups, but it’s what I had on hand and was looking at the number of shots more than just the groups.
So the question is this:
Does having the hammer strike the valve with NO spring tension against it improve shot count because of how the hammer rebounds/is pressed back by the valve? I’m starting to think, “yesâ€.
I was dead wrong about pellet weight.
Got to thinking about it on the drive home from work. IF i dry fire a co2 rifle without any pellet in it at all, it uses up the gas fast. No way to tell how fast as there is nothing to chronograph, but it sounds and feels like the number of healthy shots shots per fill is a lot less.
If I were to plug the barrel solid, could dry fire for hours, losing only the gas than manages to leak past the seals.
So a heavy pellet creates more back pressure, keeping more gas in the tube than a light one. Basically, the valve dwell is the same, but because the heavy pellet hasn’t moved as far down the barrel, the gas volume uses is less than with a lite pellet.
SO...today tried .177 heavy weights, from 9.3gr. to a bit over 11gr..
Kind of stunned at the results. NOTHING had changed from yesterday’s test of lite weights, same valve and even the same temperature (by the thermometer, it’s within 1 degree of yesterday’s test temp.).
Call it 100 good shots. Kept on shooting for another 10 shots (#101-110) to see the vel. fall off, but shot # #1 to #100 were on target in in normal vel. variation readings. Was trying for groups today, and the two outstanding pellets were the Kodiaks and RWS Supermag WC’s.
Not a powerhouse, this little rifle is getting a bit more than 8 foot pounds with these heavy pellets, so it isn’t going real fast. But those Supermags are looking mighty good for pest birding (head shots) out to my back yard 30 yard max.
