I measured the depth of the tube to the valve face.
And the distance from the end to the pivot center.
And the length of the pump assembly from pivot center to plunger face.
And then I adjusted the length...and reassembled. All that measuring got me close, but I still had to take it apart about 3 more times before I had the pump headspace set to my liking. Anyone have a better way of doing it?
Then I went to work making a replacement aperture disc. I took some rough scaled up measurements from the Benjamin book...the threads seem to be 3/16"-40. All I had was a #10-40 die but there's only about .0025" difference between those two so I just adjusted the die to cut oversize.
Knurling...
Turning the shank...
Here's the adjustable die.
It fits!
Drilling a .081" aperture hole (#46 drill). I went big because I wasn't sure what would suit my friend best.
Boring out the recess in the front. I intentionally ran it fast so it would chatter at the bottom, hopefully diffusing the reflection.
Yes, it's screwed in backwards for this shot. Oxpho Blue is awesome stuff.
Mounted on the rifle.
Another shot.
The 310 is a smoothbore and the bolt is bored to just hold ball ammo. Kind of neat.
Well it's held pressure overnight, several days in a row. I got velocities of 590 fps using the Gamo round balls (8.2 grain) and 620 fps with CPL (7.9 grain) pellets, both at 6 pumps, which is the maximum recommended. Better to just pump it up 3 times for plinking. I'll see if it holds air for a week straight and plink with it off and on before giving it back to my friend.
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