Friday, January 8, 2010

Benjamin 312 Leather Seal Shenanigans

This is a boring and pointless post that only serves to show how much I have to learn about fixing airguns...

I decided to get clever and make the forming dies for the pump cup with a hole...

and a pilot...

Seems like a good idea as the hole will be perfectly centered.

Left to dry in the vise...

All torn up in the center. Did it twice and got the same result.

Decided that maybe the lack of a chamfer on the male die was the issue so I added one.

Still torn around the hole.

And again...

So I left only the merest hint of a pilot.

Tired of this yet?

Finally! But it's too damn short. I started using a female die with no center hole at all.

And shaving the leather thinner. I need to get some already thinner leather.

Too thin.

Last chance...I soaked this leather longer than the last and shaved it thinner but not as thin as the last time. It's long enough if a bit ragged.
I won't be spoiling the surprise to say that yes, this one works. And I didn't even show the 10 other failed attempts.
So what I learned is that the smaller the cup diameter the more the leather stresses. And that I need even more of a variety of leather thicknesses. BTW, here's a great post from the Classic Camp Stove forum on making small leather pump cups.
Did I mention this cup is available for less than $7.00 from JG Airguns? But what would be the fun in that?


Unknown said...


I have the same project - an old "father-in-law" present 312. Where did you find the parts and maintenance manuals for dissasembly and re-order of replacements parts. this one is pretty beat up.

Phil -

Felice Luftschein said...

"The St. Louis & Benjamin Air Rifle Co.'s" book by DT Fletcher has all the factory literature. You can email him to buy a copy:

For parts you can try Bryan and Associates, Mac1 or JG airguns.

Tell them the blog sent you.


Anonymous said...

I've formed the cup w/no hole and used a punch after

Anonymous said...

I realize this is a very old blog and probably no longer moderated but I'm gonna give it a shot anyway. I think I may have found a cheaper alternative source for the leather pump cups but I need to know the diameter of the cup itself or the ID of the chamber for the 312, 317 and 322.