Back when I shot in HUntsville (TV) THE easiest way would be hand o=it to David Slade (Minor Hill TN) and let him do it. Yes sit that was easy and worked flawless every time.
If you have a cleaning rod with a felt on the end push it up to the oring groove and that stops the oring going down the barrel. Just work it into place with a Allen key. If you can take your barrel off that makes it even easier.
Harbor Freight sells this set of dental picks for about $3 that are very thin and soft. You can bend the tip in a slightly offset little U shape to reach in and rotate under the oring and pull it out without damage (after some practice). You might dull the tip slightly . I use a small Allen wrench to re-insert it. Much easier out of the rifle.rifle. Alternately, you can just stab it and pull it out. Have replacements on hand in either case. Bob
I think I posted this twice sorry, but I did a video, using my worm patch cleaning kit, to reinstall my oring on RW 25 Caliber Rosso and it worked great if this helps you let me know
Once you do it one time it’s not so bad. I’ve had to replace that oring in my Brocock Bantam Sniper HR a couple times. Most recently last week when I blew it out being careless. It took about 15 minutes to remove the barrel, lube the o-ring, replace it, and the barrel. I used a blunt end brass pick from a Hoppe’s pick kit to work the oring back into its groove. I don’t recommend using sharp picks to remove orings. These work quit well.
I just replaced my first breech O-ring, on a FX cutlass barrel ( the old ST barrels ) That was a breeze as it was not very deep in the .22 hole, but the other O-ring that is in there, much deeper, well that one got to be a SOB to replace. I am unsure why it is there after all as it seem to be seated deeper than a pellet would be, i can only assume as it is the old kind of ST barrel which is smooth bore in most of the barrel, that O-ring is there to prevent the pellet from sliding forward before it is fired.