"Tuned" my new to me .177 HW100 to shoot 8.4gr JSBs at 825fps. I did this by lowering the reg pressure until they were shooting in the 840 range. Then I started turning down the hammer spring until I had it in the 820 range. I ran several extra shots to make sure it was consistent.
The next day I start the sight in process. First few shots sounded normal. Then they sounded weak along with a very low POI. Pulled the chrony out and found it was shooting 411 fps. I turned the hammer spring up 1/2 turn, and did another chrony run. 1st shot was 597, then the next shots, maybe 10 or so, constantly increased velocity.
The velocity topped at 896, then each shot afterwards started dropping until it was consistently in the 840s. Then turned it back to where it was originally and it was in the 830s. I then turned the hammer spring down just a smidgen, and now it is back in the 820fps range. My hammer spring setting, if not exactly where it was at the end of the tuning is nearly so.
Anyone have a guess what happened?
The next day I start the sight in process. First few shots sounded normal. Then they sounded weak along with a very low POI. Pulled the chrony out and found it was shooting 411 fps. I turned the hammer spring up 1/2 turn, and did another chrony run. 1st shot was 597, then the next shots, maybe 10 or so, constantly increased velocity.
The velocity topped at 896, then each shot afterwards started dropping until it was consistently in the 840s. Then turned it back to where it was originally and it was in the 830s. I then turned the hammer spring down just a smidgen, and now it is back in the 820fps range. My hammer spring setting, if not exactly where it was at the end of the tuning is nearly so.
Anyone have a guess what happened?
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