johnpb
I have done it three ways. All were done because the primer seat was worn because of flame cutting. The factory plugs allowed some little blow back, and that didn't much bother me. However, after the primer seat becomes flame cut, the blow back increases and increases as the flame cutting worsens. I think keeping a rifle cleaner than i do helps keep flame cutting from happening, but i will never know, because i don't have the best habits when it comes to cleanliness.
Busta is the man that fully understands using o-ring to stop blowback. Taking advantage of his knowledge, i used a flattened 'C' drill to deepen the primer pocket of a plug so it could receive an o-ring. This should be done very carefully, so that one can sneak up on the correct depth. If the action won't close on the plug, primer, and p-ring; one drills deeper until the action will close. If this is done carefully, one can end up with reduced head space and zero; zero as in zero blow back. The o ring is compressed some, but not too much, and the seal is made.
Sabotloader made a thread where he used washers instead of o ring, and this reduced head space and therefore blow back. I did this with both stainless steel and aluminum washers. Here the head space was reduced so that there was a slight primer compression when the action is closed. This worked OK for me using the steel washers, but there was a very little blow back. This led me to aluminum washers and a head space that compressed the primer some little. This made for zero blow back and i was thrilled. However, after shot after shot the aluminum eventually failed. This led me to the next and final fix for blow back. I believe
GM54-120 still has a couple of plugs in service using this system, and they are working well for him to my knowledge.
The best way to decrease head space for me, was done because i drilled the primer pocket too deep trying to get it to work with the washers. After one drills the primer pocket too deep with the 'C' drill, one might think the only thing left is to toss the breech plug. However,
Screwbolts described using a grade 8 bolt as a method to 'heal' the damage. This involves drilling the breech end of the plug with a letter Q drill, and tapping the hole with a 3/8 x 24 tap to receive the grade 8 bolt.
These are pictures of the breech plug for my Omega, and the over all length of the primer and plug ended up being 0.011" longer than a 'new' breech plug. So, the head space is now reduced by 0.011". This results in one being able to 'feel' the primer compress when the action is closed, and this along with a nice smooth primer seat results in zero blow back. Time will tell how long this procedure lasts, but so far so good. The grade 8 bolt is hard and tough like them vent liner are, and they last a very long time on the other end where there is really a lot of heat and flame.