You gave me the courage to do an experiment I've been looking to attempt but didn't have the cajones to try until today. I didn't take any pictures but I'll do my best to describe my process....
So I have a 97K with a Vortek 12ftlb kit in it. I was running it damn near max for FT at 11.8ftlbs with JSB 8.44gr. It was always a snappy/jumpy gun even at that power level. I figured reducing the piston weight would help.
Step 1) Reduces piston weight down to 215g (45g lighter, maybe a bit more forgot to measure). Then I put it back together and fired off a few shots before putting it over the chony. As you'd probably expect, the gun was pretty bouncy. What you may not expect was was that I lost nearly a full 2ftlbs and the gun felt terrible. Back in we go.
Step 2) I open up the transfer port to 3.2mm and added a small shim to the top hat. Put it back together and back over the chrony. I gained back about 10fps but the shot cycle didn't feel much better. Definitely significant bounce still.
Step 3) Added an additional spacer to the spring made of acetal. Probably close to 3/8" of added preload now. I hade to take about that much off the PG4 guide to make it all work. Put it over the chrony yet again and bam. Back to about 790fps.... with an odd bounce!!
Step 4) Opened the TP again, this time to 3.6mm. This actually gave me a decent increase in velocity. I am now sitting at 807fps and the bounce is gone. I need to accuracy test it tomorrow but inside on my 10m targets at 27x dialed in on my scope, the reticle is staying within the 1.18" circle when the gun fires. Absolutely an improvement over before. I'll probably remove that small spacer next and see if it softens it up a hair while keeping the rifle legal for field target use.
