Originally Posted by
NickG
Did some testing with the sliding nose piston today as it's easier to alter than the inertia weight idea .
Firstly I built it with a spacer instead of a buffer and set the power ( 11.4 fpe) to give a base line.
I then put two o rings in that were sized to just slide in the comp tube power went down by. 1 fpe ,increasing the pre load sent the power lower , I believe this meant the o rings were expanding too easily on the power stroke slowing it all down , it did soften the cycle, probably because the power was down.
Secondly I put two X rings in smaller in diameter and more rigid due to the square section, had the same result, so reasoned the pressure involved must be high enough to compress them too easily.
that pretty much mimics my results... pity I didn't have the patience to go further as you did - take#3 sounds promising - keep us informed
Originally Posted by
NickG
One downside is there is a larger shot to shot spread than I like, I think it's due to some movement between the nose and the piston body, so going to button the front to keep it all in line. Hopefully that will sort it out.
The other concern here is how consitent the expansion timing will be - tiny variations, lets say in pellet fit and therefore peak pressure - may have a large affect on piston braking point and therefore fps variation. Also as that "buffer" oring ring wears through repeated pressurisation and relaxation - it's quite a dynamic, tough environment.
That's why I like the floating inertia option - much less to go wrong
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.