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

crosman 1377 double tube pumper ? about to find out ( pics

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I’m glad to see that mill in action! Somehow missed this thread till today.

Nice work going on there. Looks like you’re having fun with it and your machining looks great.

Not sure why anyone would bring up cocking force as a problem with this design….it offers higher volume per stroke and if effort is too great on the tail end, you can design in a pin that drops one side out and let you ‘shift’ into a lower gear…..

I like it.


Rob M:
thanks Dave .. well , the basic math says it wont be bad - ill be gaining 50 % lever length from the pivot hole ( the lever arm has another section not posted yet )
MA diagram by murphyrobert9, on Flickr

So ill have 1.5 MA against 2.1 ish required force to move the pistons ( the .1 accounts for the additional friction caused by surface area and 2 linkages )
So it will be roughly 40 percent harder than stock , or thereabout. im also likely to add a foster on the main block to account for future laziness

Rob M:
heres a more accurate depiction of the lever length .. and it still needs a wood handle below ( i might not keep the second arm as is , i dont like it cosmetically )

20210804_084840 by murphyrobert9, on Flickr

Rob M:
caution , im not a woodworker.. SO i decided to recycle .. this knub is off an old wrecked benjamin 342.. I chopped a piece , cut a channel , mounted it then restained it with some rub ion walnut

20210804_121011 by murphyrobert9, on Flickr

20210804_121312 by murphyrobert9, on Flickr

if theres a clearance issue during real world pumping ill trim it .

Rob M:
real world color

20210804_122619 by murphyrobert9, on Flickr


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