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All Springer/NP/PCP Air Gun Discussion General > Machine Shop Talk & AG Parts Machining

.357 Big Bore MSP Near Completion!

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Duane38:
Gang, here are a few pics of the .357.big bore pumper project.  Did some testing today and found myself to be pleased with the preliminary numbers so far.  I may fiddle with transfer port sizes to see what is best.  Right now, the TP is .25".  Here are the numbers using 81 grain JSB:

10 pumps, average of 404fps - 29.3 ft/lbs
15 pumps, average of 496fps - 44.2 ft/lbs
20 pumps, average of 606fps - 66 ft/lbs
25 pumps max, average of 695fps - 86.8 ft/lbs

Valve volume final measurement is .65 cu.in.  Each stroke is 5.3 cu.in.  barrel volume is 1.95cu.in.

Duane38:
Uploading not worthy here...

Duane38:
Muzzles...

Duane38:
Doh...

Duane38:
....

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