kerndog said:
I just recently bought a new breechplug from Metrics Unlimited, and is this plug ever sweet !!! No blowback at all ! My question is, How many shots is the o-ring they provide, good for ? I fired about 10 shots through it and the o-ring still looked good, so i put it back in the rifle, should i do this, or replace it ?...thanks
Did someone say "o-rings"?
Like Steve mentioned, the #60 o-ring at Lowes or Home Depot are all you would really need. They come in a 10 pack for $1.97.
However, if you really are an o-ring connisuer, there are several options.
All of the o-rings on the perimeter are suitable for use in the Metrics Unlimited breech plugs. They are made from several different materials, such as Buna, Silicone, and Viton to name a few. The one in the center is for my Knights. The round cross-sectioned ones seem to be better suited for the MU breech plugs. And to be honest, in this application, the cheap ones will serve you well.
You can use any o-ring that has the dimensions of 1/4" O.D. x 1/8" I.D. x 1/16" thick. You can get 100 pieces of the basic black Buna-N from McMaster-Carr for $1.94. You could easily get 50+ shots on most of them, but for 2 cents a piece, I discard them after a range session (usually 40-50 shots.
This is the cheapest o-ring you are likely to find.
http://www.mcmaster.com/#9452k14/=5n7fk4
You can check out several more here at this link. There are near metric equivalents that will work as well.
http://www.mcmaster.com/#o-rings/=5n7dvr
Here is a pic of the cheep o-ring and fired primers after a 38 shot range session with Blackhorn 209 powder. They do wash-out in the center as expected, but lose very little in thickness. IIRC, this one only lost .002" or .003" in thickness. As cheap as they are, they get tossed after a range session. For Hunting I always have a fresh one in the plug, and a couple in the possibles bag just in case.
The best thing about this o-ring is that it makes your ignition system waterproof with a primer installed. The fact that it harnesses the blowback is just icing on the cake.
I did some early testing for Nick, before these plugs were released. The 5/8" were made to shoot 777 and other powders initially. I introduced the o-ring, as I have used this idea in other custom plugs. I shoot Blackhorn 209 in my 209 inlines. There was just enough room in the primer pocket to utilize the o-ring, so I brought the idea to him, the rest is history. The 7/8" breech plugs were a later project, and utilize the o-ring as well.
Here is a prototype 5/8" breech plug with my o-ring modification.
Here is a production 5/8" breech plug.
Breech area after a range session.
It sure beats that plastic primer carrier all to heck, IMO.