Sure sounds like it is the Delrin diameter referred to in Tim's note. (And yes I now recall you had that in your excellent review that started this thread.) My #1 and #3 poppet/stems had reasonable stem lengths and 3.2 fpe difference for 0.007 diameter difference. Tim's guidance would predict a 1.4 fpe change. So fairly consistent results to his guidance.From the last little paragraph on this post....https://www.airgunnation.com/threads/mac1-usft-analysis-overview.1044226/post-1047847
"Tim sent a note with my gun that says, "0.2fpe per 0.001" diameter of valve head." I'm not sure if he meant the valve stem can be reduced by 0.001" to gain 0.2fpe or if the outer diameter of the delrin has to be reduced by that much to gain 0.2fpe. My gun is going to stay at its just under 20fpe power level so I won't every be testing out this theory, just thought I'd include it for any interested parties. "
I've got a spare poppet that Tim supplied with my gun and I'll try to remember to measure it and provide you the dimensions when I'm not at work. I've never had that spare poppet in the gun so don't know what fpe it produces, but it might be interesting to compare specs at least.
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