lower pressures = best velocities?? YES! ;D

[chanman84]

Hey guys, I went to shoot a couple strings of 10 shots through my disco this morning and decided to record my velocities. All shots are taken with crosman premier domed hollow point pellets

String 1 at around 1850psi
1. 790
2 .786
3. 789
4. 793
5. 799
6. 797
7. 805 (1650psi)
8. 799
9. 809
10. 811

String 2 continuing from about 1550psi
1. 818
2. 806
3. 811
4. 812
5. 809
6. 811
7. 807
8. 805
9. 797 (1150psi)
10. 793

I'm getting my best velocities at around 1600psi down to 1100psi. I was always filling to 2000 before I got my chrony but now I just fill to 1600 and it's just awesome not having to pump so much! This trend seems to be the opposite when using my home made power adjuster. The higher the psi, the more power I get and the curve is not quite a bell curve as a stock disco, but rather a declining linear curve. Here's what I mean.

Same CPHP WITH power adjuster starting at 2000 psi fill 

1. 968 
2. 947
3. 937
4. 931
5. 934
6. 921
7. 914
8. 893
9. 885
10. 871
11. 858
12. 844
13. 822
14. 806
15. 708

I think I found a happy compromise by backing the rear screw all the way out and leaving only the spring guide rod giving a bit extra tension on the valve spring. This gave me much more efficient use of air and shots per charge as compared to the previous string before it.
1. 862
2. 866
3. 875
4. 877
5. 881
6. 879
7. 879
8. 864

Just as a point of reference for those of you always topping off your disco, sometimes its better to shoot at the lower pressures for best results. A chrony however, makes tuning much easier and no longer a guessing game. Cheers.
-Roger

[rsterne]

In theory, the "proper" way to use a non-regulated PCP is to pump past the point of maximum velocity to where the valve is in "partial lock".... ie it is being closed by the extra air pressure.... The gun is actually more efficient, and therefore quieter operating that way.... plus you get more shots per fill.... I use the point where the velocity is 96% of the maximum for both the fill and refill pressures....

However, if you only want half the number of shots per fill and easier pumping.... there is nothing wrong with filling the Disco to 1600 psi instead of 2000.... The "declining linear curve" you refer to is the result.... If you want just a few, very consistent shots.... then work with the middle section only of the bell curve.... That is what you are doing in your last shot string....

Bob

[Rickey]

Are yall pumping your Disco by hand?  How long to fill it up?

[chanman84]

I pump by hand. It only takes a minute or two to pump it back to full from 1000psi.

[Bryan Heimann]

probably saves a ton of wear and tear, pumping only to 1600 psi.  i see a lot of posts about pausing every 25-50 pumps to let the pump cool off in order to make it last longer.  if you just figure out how many  pumps you need to get those ten best shots and keep the pressure in that window, the pump will naturally get it's needed rest between shot strings.