.25 JSB Kings Power Tune and General Musings

[Bullfrog]

I've spent the past two weeks playing around with tunes for Kings. Usually I don't shoot Kings because I favor heavier pellets with my power tunes, but as I currently have a big supply of them I thought I'd give a go. Here's where I ended up as of this afternoon:

.25 JSB Kings
A2A valve
Hill depinger and free flow gauge
Gaska/WAR air tank extension
Factory hammer, 12.5# spring
Transfer ports drilled to .18
Spring tension - full CCW (0 spring tension)
Hammer stroke - full CCW (max hammer stroke)

3000 psi fill

1. dry fire (to test depinger after re installation)
2. 947.5
3. 953.1
4. 962.3
5. 959.5
6. 965.9
7. 974.8
8. 965.8
9. 979.2
10. 986.3
11. 983.5
12. 978.1
13. 989.3 -2600psi
14. 983.7
15. 983.2
16. 974.6
17. 972.2
18. 972.8
19. 970.2
20. 965.0
21. 960.1
22. 959.1
23. 949.5
24. 944.3 - end 2150psi

From here I can either shorten my hammer stroke for lower numbers/more shots/lower fill pressure or increase my spring tension for higher-power/fewer shots/3200-3300 fill pressure. Its easy for me to remember my tunes when I can have a base tune that has the spring tension minimum and the hammer stroke maximum. I can adjust one or the other without trying to do both at the same time and forgetting my tune settings.

I would say that's a darn fine tune. I bet Barracudas will really shine with it.

Here's where my general observations come in. A few months ago I was able to max my FPE levels out for 4-5 shots in the mid 90sfpe by overfilling to 3400psi at max spring tension and hammer stroke, with 80fpe at less spring tension and hammer stroke being a more efficient and practical tune for an entire clip from a 3200 or 3300psi fill. Its from the 80fpe tune that I did much of my hunting from over the summer. Then back around Christmas I went inside the gun for some reason I don't remember and found that the oring that sits on my valve stem was broken. The oring stops the valve from opening all the way. It limits my max FPE but also makes for flatter shot strings. I replaced the oring and also added a depinger and BHB buffers. I was able to get 24 very flat shots at 50fpe with Barracudas with the BHB and I never tried to max it out to see what it would do. I then took the BHBs out at tried to set my gun up for max fpe again. Initially I was able to max out at 80fpe with decent efficiency and every few days my max fpe would decrease down to the best it could do was 65fpe with good efficiency and could do 70fpe at 100psi per shot. I couldn't figure out why my gun was losing power potential on max settings, while at the same time maintaining consistent power and air usage at lower fpes.

I then got to thinking about my depinger. I opened up my air tube and found that the depinger had worked its way down to the gauge block. Originally I had installed it midway down the air tube. Over a few weeks it had worked its way as far back as it would go. I figured it was the reason my max fpe potential was falling off so I took it out and also added a max-flow gauge block.

To my shock, I received NO increase in power by removing the depinger and switching to the max flow block. What I did receive was a boost in efficiency at high fpe settings. When the gun was maxed out with the depinger it was costing 100psi per shot to make 72-80fpe (fpe varying on the projectile). Without the depinger and the high flow block it was costing me 50psi to make the same energy levels on max settings. I believe this is because my valve relies entirely on the air tank's pressure, not a valve return spring, to shut it. When the air moves freer in my air tank, the valve can shut faster.

I put the depinger back in today and the above string was the results. I didn't try maxing it out. I will do so in the future, but for now I'm going to try hunting with it on this power level to see what it does. I am beginning to suspect that the entire time I was easily producing 80fpe-95fpe in the summer it was because the valve oring was broken. It may have been broken as far back as August when I killed the hog. I do remember that I had the gun set on 80fpe with bullets when I killed the hog and it had plenty of spring tension to spare. Its the only variable I can think of that's left to change that would explain why my max fpe levels have dropped off from 95fpe to 80fpe.

[Bigtwin69]

looks impressive to me. In the future I might tweak my 25 cal...having too much fun bust'n birds over and over (in the wind) at 50+ yds. Mine is a Gen 2 so I assume I wouldn't need a depinger. Where did the cutom/mod parts come from?

[oldpro]

Replace the poppet it's probably sticking to seat. Look at patch ring on bottom of poppet head to see if it's digging in. Should be faint line.