Other than the weight, and the added complexity and cost, an ACP is a very nice solution.... It has to be heavier and more expensive than an equivalent PCP because of the addition of the pump and check valve.... On the other hand, you don't have to carry a pump or pony tank separately.... My Millenium Pumper is a good example of what can be accomplished by combining the PCP components of a Disco with the pump parts of a Benji.... plus a few custom parts as required.... http://www.gatewaytoairguns.org/GTA/index.php?topic=39328It incorporates a fill fitting so that it can be filled from a tank when one is available and then just topped up in the field between shots.... again a good compromise.... You can call it an ACP or a PCP with onboard pump.... either way, it's a great combination.... Bob
Assuming you are already getting 17 FPE (618 fps) in .25 cal with a 20 gr. with your 0.13 CI valve, the spreadsheet says ~ 19.2 FPE (657 fps) with a 0.16 CI valve and ~ 22.7 FPE (715 fps) with a 0.22 CI valve.... All those are at 1500 psi, with an 18.75 barrel in .25 cal, having a volume of 0.92 CI.... Your valve volumes work out to 14%, 17%, and 24%.... so they are all pretty small for a .25 cal.... I would try and get up to about 0.30 CI if possible.... That should put you at about 26.2 FPE (769 fps) with a 20 gr. pellet.... I looked at my initial results for my .25 cal Disco pumper carbine, which had a 20" barrel, and at 1500 psi it shot 665 fps with 25.4 gr. pellets (25 FPE).... It had a valve that was 5.5 cc and a barrel volume of 16.1 cc, so that worked out to 34%.... That also means that my estimate of 26.2 FPE at 1500 psi with an 18.75" barrel is probably slightly too high....The basic variables in the spreadsheet are caliber, pellet weight, valve dwell, reservoir pressure and volume, transfer area volume, barrel length, pellet drag and starting force, the gas used (air, nitrogen, helium, CO2), and an efficiency factor which usually runs between 55-70%.... The normal procedure is to input the known quantities, use default quantities for some of the minor ones if they aren't known, and then balance the dwell and efficiency until it matches what the gun is doing (or what is normal).... For a dump valve, the dwell is simply selected so that the valve is still open when the pellet leaves the barrel.... I had to use an efficiency factor of 67% to get your gun to deliver 17 FPE with the 0.13 CI valve, and that is not unreasonable for such a small valve.... The calculations are just straight F = MA, done every 0.000001 sec. as the pellet moves down the bore until it exits, correcting for the new pressure as the air expands behind the pellet.... It takes into account the weight of the gas behind the pellet accelerating as well.... The spreadsheet has had MANY revisions and refinements, and I feel it represents a VERY good model of what is going on inside a pneumatic airgun (CO2, pumper, or PCP).... Bob
If you are asking what changing the caliber ONLY will do, I can give you a rough idea.... I need to know the pellet weight and caliber currently and in .25 cal.... and the pressure.... From your post I will assume both have an 18" barrel and 0.20 CI valve.... The current FPE levels as a dump shot and for 2 shots MAY be enough information, but doing the dump shot shouldn't be too hard....Are you REALLY getting 14 FPE on a 2289 pump with only 10 pumps?.... The best I did with an FTP, 14.5" barrel and 14.3 gr pellets was 541 fps (9.3 FPE).... That was quite a while ago, but 50% more than that is quite astounding, even with an 18" barrel....Bob
and the pressure?.... If you are using 10 pumps on a 2289 pump, which has a swept volume of 18 cc, that is a total input of 180 cc.... If your valve is 0.20 CI = 3.3 cc, at 100% pump efficiency that works out to 180 x 14.7 / 3.3 = 802 psi.... At 70% efficiency (typical), that is only 561 psi.... At 802 psi, that requires an internal efficiency of 90% to achieve 14 FPE.... At 100% efficiency, the minimum pressure to deliver 14 FPE in an 18" barrel would be 718 psi.... That requires a pumping efficiency of 718 / 802 = 90%....I repeat, are you SURE you are getting 14 FPE on 10 pumps with a 2289 pump?.... If so, you have achieved greater efficiency than anyone else has ever managed....
OK, read your response, and since you are SURE, then with a caliber change ONLY, and assuming a 20 gr. pellet (I asked but you didn't answer) you should get 610 fps (16.5 FPE).... I would strongly suggest you carefully document all that you did to achieve 90% efficiency with your 2289.... as you should be starting your own airgun company.... Obviously you don't need my help any more....Bob
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