Oring sealed piston cap questions & personal opinions.

[nced]

Question from the ".20 Calibre" thread (rough paraphrase)........
"did you use the same oring groove width with a 1/16" cross section oring as a 3/32" cross section oring"

Well....in the beginning I made the width about the same as the oring cross section. For years since I've used a groove width width of .080-.802 wide (for a .070 nominal cross section) instead of the more normal .093-.097 wide.
Anywhoo....I only used the 3/32" nom cross section oring for a couple days, then replaced it with a 1/16" nom oring since there were disadvantages to the "fatter oring" such as more drag on the piston resulting in lower velocity.

Initially, when I started messing with oring piston seals to lessen "temperature induced poi shifting". Later I also found a benefit where I could use a lighter wire spring in my .177 R9 and still maintain the same velocity as a heavier wire spring if I was using the old HP seal design incorporating a thin parachute edge. Also, using the single 1/16" cross section oring it only took a couple shots to stabilize the poi unlike the factory parachute seal that required a couple dozen shots to stabilize the poi (that was in the days of using molly paste and spring tar).............


LOL....here is a pic of the very first oring sealed piston cap I made decades ago in WV using a small Harbor Freight desk top lathe next to a factory HW piston seal at the time. I didn't know how the aluminum face of the piston cap would hold up to hitting the end of the receiver so the gun was broken down after about 1000 shots for a "look-see"..........

As you can see, the only marks on the face of the cap are "combustion colors" from the days of using molly paste as a lube.
 

[stevevines]

Very interesting Ed, I love reading info such as this, and am glad I found where you're hanging out, forum wise, these days.

[bandg]

Yep, certainly innovative and nice work there Ed.  My thought was would the 3/32 o-ring have performed better with a groove cut specifically for that size o-ring?  Could the 3/32 o-ring have been compressed much more heavily in the original groove than is the 1/16 o-ring and thus possibly increasing drag greatly without adding to seal?  Do you think overall that the o-ring approach has true advantages over the more common seal?

[A.K.A. Tommy Boy]

Good Idea....Smart !   Nice work Ed.   Very innovative thinking & practical application.     Having machining equipment at your disposal is real handy.                         

Best Wishes - Tom