The 1377 Project, MKII Piston, Part 1

I decided to revisit the 1377 carbine project. I was never happy with using an o-ring as a pump seal, as it drew vacuum on the back stroke. So I decided to see if the original seal could be modified.

My old piston and two new seals (cheap from Crosman).

The pressure wasting cup face is obvious.

I took one of the plastic pistons...

And sawed off the end.

Turned away a bit of the plastic.

Voila, a piston cup chuck.

Putting a cutting edge on some brass tubing.

Drilling a hole in the pump cup.

That worked well.

Trimmed off the back of the cup.

I need to figure out a more precise way of doing that.

You can see how the brass drilled/punched a good fitting hole.

I cut a couple of shims for later. The drill catches the rings as they are cut off.

Looks like the conical recess is about 90 degrees.
More to come...