This whole problem is my favorite method of counting sheep! It's was a big "duh" moment when I remembered the hole through the rear piston...stupid me, but I tend to get focused on one element of a mechanism and don't see the forest for the trees...
My only worry is that the .3mm figure, while correct for the 75, is somewhat larger than needed on the smaller pistol, the spring forces presumably being less than on the rifle.
Using hand pressure (as opposed to the rack and pinion which give far greater forces) on my arbor press handwheel, and measuring the amount of compression on the rear seal, I get a figure close to that (.008"/.2mm deflection as opposed to .0118"/.3mm) but there is no way for me to know how comparable the forces are. In any case I hope that a few thousandths either way won't matter.
This mystery largely solved it only remains to make the rear buffer element that goes between the cap and the washer. I'm thinking hard rubber sheet, and then shimming as needed to get the existing lock screw hole to line up. Presumably the compression of this rear buffer also figures into the overall deflection, which complicates things a bit, but also likely gives some wiggle room.
Nick,
From ruralburbian Philomath.
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