Any time I tried inserting the ram cap (straight, rolling, etc), it never worked. The o-ring would *always* get pinched putting it back in. Now if I took something thin and pushed it in a bit, it'd fit fine, but the last thing I want to do (or should have to do) is deal with something like that.
So I purchased two different o-ring sizes. One was 1x14 and the other was 1.5 x 13. The 1.5 x 13 would give the same OD and fit tighter to the cap, but be thicker. The 1 x 14 would fit the cap the same, but the OD would be a bit smaller and hopefully not catch on the body.
1.5 x 13 seems way too big, but the 1 x 14 fits just fine. I've only aired it up and dry fired it a few dozen times, but so far, it's holding up enough. I can see a small amount of grease being pushed out between the cap and body, though I don't know if it's due to the o-ring or the fact that I swapped the screw with a thumb screw; I'll have to continue to experiment. So far though, if there's any air loss, it's not audible. I'll put some soap/water on there to see what happens, but in general I wanted to see if anyone else had experience with doing something like this.
If you want to set off and go develop some grand new thing, you don't need millions of dollars of capitalization. You need enough pizza and Diet Coke to stick in your refrigerator, a cheap PC to work on, and the dedication to go through with it. We slept on floors. We waded across rivers. -John Carmack