Benjamin 347 pump seal repair
I don't often work on airguns though I have a couple. A friend needed repairs on a vintage gun, a Benjamin 347, same system as several other Benjamin models.
I ordered one of the repair kits off the internet from Airgun Warehouse that comes with the seal removal tool and also replacement pump piston cup. The gun uses the rubber cup that pops over a stud on piston rod, the new seal was the other [later?] type that's captured around its circumference.
Didn't want to wait to get the right cup, so I looked at it and decided to experiment. I used my hole punch, good quality Made in England, multiple punch spindles, to punch a hole dead center in the rubber pump cup.
After cleaning the mounting area & stud I placed pump rod in vice with other end firmly against table, used a drop of Palmolive liquid as lubricant because that won't harm rubber or gun parts, but a guy could use vegetable oil too I guess. Forced new cup down over stud with a little help from a screwdriver. Popped right in place, holds very securely and no chance of it coming off.
The particular punch spindle I used is .250" or 6.5mm, perfect fit, slightly smaller than pump rod stud diameter. Took quite a bit of clamping force on pliers-type hole punch tool, had to rotate cup on spindle to punch evenly all around.
Works great, excellent pressure. Please feel free to copy this to any relevant airgun website so it may help the next person?