Breech seal shimming.

I noticed up front that the o-ring seemed flush with the breech. I wondered if it was getting a good seal.

A little google-fu revealed it is not an uncommon situation, and shimming via a washer, dental floss, plumbers tape, were all ways around it.

I have plumbers tape and floss on hand, so went with the floss. Removed the o-ring with a straight pin pry up from the outside edge. To get the floss down into the channel, I took about 10 inches of floss, and loosely wrapped it around a 44Mag case. Put the mouth of the case into the channel and pushed the floss off, and into place. Then put some silicone grease on the floss, and o-ring, and replaced the o-ring.

That left the o-ring a bit proud of the breech face, and I can feel it seal up on closing.

I chrono'd after, and gained about 30 fps with both the 14.3gr and 18.1 gr pellets. (820/720 fps fps respectively after). Chrony was being a little difficult (15F here today), but results seem good.

Pic after,
[Linked Image from i.imgur.com]