In case I wasn't clear,I do want one of the 13xx pistons with the end seal and a groove for a back up O-ring, two 3/8" wide .545 deep grooves for teflon. I'll need alot of extra of those types of end seals also... Along with that other long piston of course. Let me know how it's coming along.

Add on.

Drill and tap the piston end then screw the seal on and your done, that allowed for the back up seal and the front seal

Send the tubing you want to use and I will finish your piston all that is needed is to cut the grooves for the bushings

Maybe I didn't see how it was held together in the picture. I'll wager a guess and say that the drilling and tapping needs to be in the exact center of the piston, and the odds against me doing that without a lathe are slim to none, so I might need to have you do that for me,or maybe, just make me another piston that is set up for the new type seal-O-ring combo. The piston I made for my 1322 works ok but a much better one can be made on a lathe. So if you can maybe mod one of your other pistons to work or something that would be good. What ever it costs just let me know,I pay my bills!

Send the tube? Do mean send the stainless tube I honed for this next project?
I can use the valve as a guide to get me the final demensions on the ID of that tube,I would say it's very close to stock size,maybe a hair under,were talking tenths here. My valve is .617 and it's not tight but very close. For the piston OD .6185 at the most. But since I don't want the piston touching the tubing, the OD at the O-ring end can be .6185 but above that it should be .610,rememeber that the shrink teflon fills in what ever space is left over so the piston OD above the O-rings doesn't need to be .6185. Thanks for the help.

I mean the shrink teflon It makes it much easier when working with variable sizes in this way I could keep all inline.

as far a placement of the end seal it makes it easier if you have jigs to guide your work and cnc to center it then it’s just a matter of boring the hole.

But you know the old way was to do it by hand measure and mark measure and mark measure and mark then drill.

But we both know that for getting a hole dead center a lathe really is the best and easiest.. But maybe we can come up with a custom design piston using one of those seals or something similar. I do like the ones that snap on a big tapered pin like the springers are using though. There seems to be alot of those seals in springer size so I'am sure they can be had in 5/8" for a crosman pumper. Must get rid of that last bit of head space!