First off, great forum. It has really given me the confidence to mod up my discovery and now my Hatsan. So a big thank you to the moderators and the posters. I figured I would share my results in hopes that it might help someone else. I am resurrecting this post so as not to start a new post on the same subject. I hope that is ok.
I also followed rsterne's advice (link was already posted) for my .25 at44-qe long and I too am doing it to regulate the gun. I use it to plink with as well and I am unhappy with the quantity of shots. I recall 40 being on airgun depot's website when I purchased it. I just checked and it says 20-25, which is still a stretch. I could get maybe 15, which is just too few for what I use it for.
I just wanted to point out a few things that I noticed when following rsterne's advise.
1. Mine did take the 6-32 set screws. I did have to enlarge my holes a little bit though. I put the tap to the hole and it just looked too small. I tried a #36 drill and it didn't fit, so I drilled them out. The 3/16 set screws were too long for my valve. Either I couldn't get the valve screwed in or the stem would seize up. I would get the next size shorter. I had to sand all of mine down about .03".
2. I had to take off about .005" from the main tube to get a hole to align. This was probably the easiest part.
3. The delrin piece at the back of the valve is a pain to get out. I used channel locks and buggered it up a bit. I added the flats with a file to make it easy to remove next time.
4. Hole sizes: barrel=.1875" or 3/16; breech=.185" or #13; Transfer port=.182" or #14; Valve hole =.180 or #15.
5. I drilled out the poppet? valve seat? (small delrin thing in the valve with an o-ring around it) to .204" or #6. I wouldn't recommend this. I'll explain why. When I got the valve all assembled. I went to fill...off the gun of course. It leaked (audibly) until about 150 bar. Then the noise went away. I set the valve aside and checked in the morning and it had leaked about 25 bar. By the next day it was empty. I took it apart to see what was wrong. I couldn't really find anything wrong. I cleaned it up and tried again. Still leaking. Took apart again and found that the poppet was nearly impossible to remove. After drilling it out, the ID is about the same size as the piece in the valve that it sits against, so trying to get something on it to push it out from the gun side is impossible. So I approached from the air tube side with a hooked poker thing. I was able to get it out, but not without destroying it. I grabbed the spare and pushed it in there. It no longer leaks. My guess is that the taper on the valve stem only has so much area to contact the poppet. Drilling out the poppet, reduces this contact area. My guess is that .204" is on or close to the limit? I'm also not as good as a machinist as rsterne, but I couldn't see any issues with mine, so not sure why it failed? Turning down the valve stem is probably fine, but it probably has a limit as well. At some point it will be too weak to function properly.
6. Don't lube the o-rings in the valve. I did out of habit. I noticed right away something was wrong when I got it all assembled and pushing in the valve would cause the valve to stick open. It would eventually close, but it wasn't responsive like it was before I lubed them. A little hot soapy water fixed this.
First shot string. No preload. JSB heavys 34 grain with all mods described. Resulted in 9 usable shots. Based on this group, more preload would make it worse? Seems as if I'm starting from the top of the string. Do I need to shave off a few turns of the spring? This hammer spring does seem overly tense. If I ever left the gun with less than 100 bar in it, the hammer spring would overcome the valve spring and drain my tank. It happened a few times. Maybe it was a bad seat to begin with?
Shot # Velocity
Not the greatest shot string of all time. Here comes regulation. Now I had some issues with the chrono as the sun was setting, so I had to put a light on it and that only seemed to work sometimes. So I put err for when it wouldn't give me a value.
So, somewhere between 34 and 36 use able shots. However, only mid 30's for energy. I have a feeling I should have purchased the .22 cal. I would have had this right out of the gate.
Oh well, I'm learning. I did get one group at 30 yards before I had to put her away and there was just one hole on the paper, so that's good, but it did that before at 30 yards. It will be interesting to get it out to 70+ to see how she really performs. I am also wondering whether I need to drill a hole in the tank. Roy said I could try it without. The string does seem odd in that it starts high and then decreases, not entirely constant. Maybe I need to wait longer for the plenum to fill? Oh speaking of plenum, it is 3.12" long, OD=1.0", and wall thickness is .055". My tank ID is 1.02".
Big thanks to Milo 74 for the regulator. Install was easy and price was reasonable.
I'm open to any and all feedback or suggestions. Just trying to maximize my fun and take out some starlings and ground squirrels in the process. I'm thinking my plenum is more than the 1:1 ratio I've read about, so maybe back that off and turn out the regulator a half turn. This will free up more space in the tank and increase my velocity. Hopefully to get back into the 40 ftlb region.
Now I'm just rambling. I'm off to bed. Thanks again everyone!!!