I found quite a lot of free play between piston and sys tube nearly all the time.
So generally I DELRIN plug the shirts of my pistons at 4, 6 and 12 o'clock. Edit: 12, 4 and 8 o'clock.
And yes - it makes a difference.
If case hardening is preventing drill I warm the skirt up with a small gas burner until it starts to get redish then let it cool down slowly.
Drill the three holes and thread them 5mm. De-burr in and outside. Dont worry about some grinding marks at the outside as there will be no more metal-to-metal contact.
I cut three pieces of DELRIN plugs - 6 x abt. 20 mm and thread them too on on side. Threads must be absolutely clean of shaves.
After that I do a real proper degreasing on all the parts with break cleaner.
Metal and DELRIN threads get cured/primed with some acid.
Common superglue (cyanacrylat) is put on the threads of the DELRIN plugs and they are screwed into the piston. Let it cure over night.
Excess on the inside gets cut to a max and carefully grinded flat following the shape of inside of piston.
Excess on the outside gets cut leaving about one millimeter proud. This excess is gradually grinded/sanded down (near the completion of the process in miniscule amounts) until the piston fits the sys tube to its best.
Finally polish the piston.
The whole process irrespective of curing time takes me not more than 1 to 1,5 hours.
Material cost - nearly nothing.
After thousands of shots in different break barrels and underlevers - mainly HWs - all the plugs are still fine, no wear at all.
Here some pictures of different executed projects.
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