New to tuning, need low tune for Gen 1 .25...

[JohnL57]

Just replaced a rusty airtube & tried Brian's low tune:
VSM 2.25
H 2
HT 5.5
2500 psi fill, after two mags pressure is still at 2000 psi- obviously could get more power, would like 24 usable shots from a 2500 psi fill. What should I adjust first? Haven't chronied yet, but I have one.
Thanks,
John

[JohnL57]

Low Tune Update: Did some digging here and found the Improved BLT, H 3, HT 6, VS 5. With a 2600 psi fill my string started at 776, peaked at 829 (shot12) and went back down to 796. Definitely saw some POI shift at 50yds. Tried backing off the H to 2.25 and got 750 at start, peaked at 814 (shot17) and ended at 791 (1600 psi). if i fill to 2200 I get two mags starting at 790, peaking at 814, and ending at 791. I can live with this, but would love another 8 shots. What should I try next?
John

[caniborrowsomeammo]

RayK is getting 40 shots with his first gen I believe. But he is using a 3100 fill.
When YOU say 2600 fill are you talking gun gauge or tank/pump gauge? The gun gauges are usually not very accurate, the gun I worked on yesterday read high- ie: tank gauge 3000# gun gauge 3700#. When tuning that will present a problem.

[StefanMD]

Low Tune Update: Did some digging here and found the Improved BLT, H 3, HT 6, VS 5. With a 2600 psi fill my string started at 776, peaked at 829 (shot12) and went back down to 796. Definitely saw some POI shift at 50yds. Tried backing off the H to 2.25 and got 750 at start, peaked at 814 (shot17) and ended at 791 (1600 psi). if i fill to 2200 I get two mags starting at 790, peaking at 814, and ending at 791. I can live with this, but would love another 8 shots. What should I try next?
John

You should copy entire string in a post and starting/ending pressure to we see what can be done!

Also, if the initial speed are to low in relation to your max speed you should fill the gun a little lower...

[zaphod621]

The original BLT that I came up with and still use was to allow me to either hand pump or fill with a 3000psi scuba tank and still have enough power for pesting around the house and keep the .25 quiet. It does that and still gives me three mags (24 shots) within 4% of peak speed. The key to tweeking it for your gun is making very small adjustments to the Velocity Screw. I found having it choked down to 2 turns out or close to that results in a flattening of the peak that gives a nice long flat peak of about 16 shots in the middle at 1% and that's where the real accurate shots are. You may have to play around with that Velocity screw a bit to find the setting your gun prefers.

I also found I could get a few extra shots by adjusting the hammer spring pre-load a little higher to help reduce the hammer bounce I was getting at 2.25 turns in. I ended up setting mine to 3 turns in and I can hear the difference in the "burp" you can hear when you have too much bounce. I chronyed it and was indeed getting a couple extra shots out of it but it tends to increase my fill pressure requirements a little and still maintain a balanced bell curve. I am filling to 2600 now but it still suits my original intent of the BLT. I average 761fps with JSBs at 32fpe at the muzzle that's plenty of power, in fact too much for most of my shooting as it passes clean through a tree squirrel and really whollops a pigeon at 60 yards and still has 29fpe retained. Shot string begins at 741 peaks at 772 and ends at 748 with 24shots. I manage 2" groups at 72 yards (my range extent out the back door) sometimes smaller when I try real hard.

Hope that helps
Brian in AZ