An even easier way to do it is to pick up a dowel rod from ace hardware. Cut it square and cut off a 3/8 piece from the end. both need boo be flat as possible. The rod should be small enough in dia. to easily slide down the bore.
After removing the bad o ring, Put a new one inside the breach area of the barrel. Using the short piece of dowel, press it past the o ring grove. Place the long rod in the bore, and while holding the short piece flush with the breech, contact the o ring with the long rod..Now gently push the long rod toward the breech. You will fee part of the o ring slip into the cut. Now jig the two pieces of rod back and fourth. the o ring will magically slip into the o ring grove. Done and done, and at the bench shooting an o ring failure no longer requires you to remove the scope/ barrel and a re sight in.
Takes a while to describe, but takes less than a minute to do. Keep the dowel rods as you would cleaning supplies, as . It "IS" going to happen again. LOL ;<)
Knife
