I've seen +/-3fps offset from optical chronys shot in a line (i.e. measuring the shot). When I rearranged my chronies, the offset was reversed, but the same magnitude.

You might have also switched bb manufacturers, or used pellets from a different manufacturing lot too.

I was considering a new product idea along the lines of solving the wind up issue a while ago. I was thinking of mounting a microswitch to the tip of a spring guide which would detect if the piston was mostly cocked. The microswitch would control MOSFETS which would keep the motor running until the piston was 2/3 cocked. Never got around to developing the idea because I'm occupied with other products though.

The benifit of a sensing spring guide is that you can disable the recock by turning off the FET input and decock the ASG by firing in semi mode. You can also do funny stuff like run a shot counter and have a counted 2/3 round burst instead of the usual timed motor delay like the SIG 550/551 series. I also suspect that a sensing spring guide would also solve the occasional semi auto jamming problem which now field cleared by switching to f/a.

Only room for 2 ideas on my stove at a time though. If I put too many on, nothing gets done because I blow too much time switching projects.

The “J” battery mod and NiCds is a straight forward solution to this issue.

Haha I should have suggested something similar. I'm running twin parallel 11.1v 1500mAh LiOn cells in my P90. Now I remember why I didn't bother with a sensing spring guide.