Reducing the hammerspring energy slightly produced a 10-shot chrono string with the following stats's:
Pumps between shots = 3
Average MV = 733fps (14.3gr Crosman WCs)
Average ME = 17.1fpe
Air Consumption = 9.3 bar-cc/fpe.
Very satisfying - I think this may be the ideal state of tune for this rifle. It's definitely time to get away from the chrono and do some shooting that's more fun!
However, there's another experiment I did last night that's too good not to share.
At one point, I installed a considerably longer spring - the stock 392 part. I only did one shot with it in place, because that one shot dumped all 1200psi = ~23 strokes = 1150 cc of air that were in the valve!
And here's the interesting part: The muzzle velocity for that shot was only 847fps = 22.8fpe.
Recall that, when set up for 4.5 strokes between shots, the gun was producing 824fps and 21.5fpe. Increasing the air expenditure by 400% therefore only increased the muzzle energy by 6% and the MV by 3%.
Why was this so? Where the heck did all that air go (other than into an ear-splitting muzzle blast !!)?
James Perotti's and my opinion, that I'll elaborate on later today, is that the answer is summed up in two words: Sonic Horizon, and this graph.
More later.
Steve
This message has been edited by pneuguy from IP address 70.144.178.41 on Dec 3, 2006 10:24 AM
(Login pneuguy) Crosman Forum Member 70.144.178.41
Right. But sometimes I think that makes exactly two of us. LOL!
December 4 2006, 8:29 AM
It's a difficult concept to accept that the pellet can be only a fraction (like 1/3rd) of the way down the barrel, but already beyond the point where any extra air can contribute to propulsion.
Consequently people carry on designing powerplants with dump valves as if it weren't true.
Re: Right. But sometimes I think that makes exactly two of us. LOL!
December 4 2006, 11:04 PM
Makes sense to me. What was your maximum predicted velocity with air again? The 15cc valve is making 25% more power, and I'm anxious to try the plastic sabot pellets out. If your graph is correct, there should be very little increase in velocity. With the huge gains I measured, I'm wondering if I didn't make a mistake by machining the new valve the same volume as the barrel.
(Login SifuSkyler) Crosman Forum Member 207.69.137.34
Now that is weird...
December 4 2006, 12:24 PM
Using the stock valve with some added volume and flow, I get about 875 with 14.3 grainers at 15 pumps. I would have thought that dumping all that volume would make for quite the bangstick. Perhaps a longer barrel is in order.
(Login pneuguy) Crosman Forum Member 70.144.178.41
The reason you get more FPS, Skyler, is that 15 pumps into a stock valve volume...
December 4 2006, 2:09 PM
...is generating much more than the SV's 1200psi operating pressure - probably more like 2000psi.
And you're absolutely right - a longer barrel would make it possible to utilize more air.
Not, that, I personally would have the slightest interest in such a mod. More barrel would increase power at the amount of that I want to input between shots, only infinitesimally. Nowhere remotely worth the extra weight and encumbrance, IMHO.
!!)?
