I finally got a semi helpful reply from PE customer service
Good afternoon *****…
Unfortunately, I’m afraid that I can’t help you with a specific size for that O ring.
These spool shafts came with the O rings pre-installed. As such, we did not have spare O rings.
The best that I can offer is to sell you the complete Spool Shaft.
Originally, the spool was priced out at $114, but I am more than happy to sell you one for $35 as this is a part that likely you won’t be able to find anywhere else.
Please let me know if you would like to proceed.
Originally Posted by CCMachinist
When I started doing shells for my revolvers the apparent thing i noticed was the hole size in the cartridge controlled the velocity of my paint.
TL;DR hole size controls how fast balls get spent