"DrPutz"So I did quite a bit of troubleshooting this weekend on the Bantam. A couple of full disassemblies and I think that I have the valve leak resolved - I suspect there is a burr or the valve taper was cut a bit wrong. Anyway, first couple of string no leaks. The leaks do not amount to much, but annoying. Here's the upshot:
- I opened up the transfer hole to 0.133 (3/4 of .177), but not the barrel or the power adjuster.
- I kept the much lighter valve spring (.026″ wire diameter spring 1″ long), though it did not want to seat on the initial fill - I had to dry fire a couple of time to get the valve to close.
- Based on the slow motion videos and heavy cocking effort, I ditched the SSH in favor of a short strong spring. I had to drop back to the 0.054" spring, due to the higher speeds from the transfer port opening. Now easy to cock, which is what I wanted.
- The hammer screw is 0.062 above the inner hammer top.
The tune turned out to be pretty good: 827 to 800 fps (3.3% var), 65 shots on 30 bar (180 to 150) for 19.7 fpe at 1.46 fpe/ci. I might have to up the fpe a bit for the JSB Monster MKII's, since they are shooting about 10fps slower than the MKI's. Supposed to warm up this week, so hopefully some range time in decent weather.