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rsterne · Moderator

I ordered a .25 MRod barrel for a new project which required fitting it into a Crosman Steel Breech.... It turns out this is pretty simple if you don't mind a slight alteration to the breech as well....

The MRod barrel has the transfer port 0.050" further from the end of the barrel than the standard Crosman 13XX/22XX/Disco barrels.... You can't just machine off the end of the barrel to make it line up or you will ruin the O-ring groove in the barrel.... Instead of having an O-ring on the bolt, the MRod barrels have the O-ring that seals the bolt inside the end of the barrel.... My solution was to grind the end off a 7/16" drill (to make it work like a long mill) and drill the breech 0.050" deeper....

The MRod barrel is 1/2" OD instead of 7/16", so it has to be machined down to fit inside the breech.... That is pretty simple if you have a lathe.... Since I was using a Disco breech I was able to hide the shoulder inside the recess in the end of the breech.... If you are using a 22XX breech you will have to machine off about 0.1" more length and have the shoulder right at the end of the breech.... The bottom of the barrel ends up flush with the bottom of the breech, so the barrel will touch the main tube, requiring the barrel band to be bored out to 1/2".... It will end up with no web in between the holes once that is done....

Once I had the transfer ports lined up, I ran the set-screw in to make a mark on the barrel, and filed a notch at the set-screw location.... That is important, as otherwise the mark from tightening the set-screw will make removing the breech difficult or impossible.... I will need to make a new 1/4" diameter bolt with the appropriate length probe to seat the pellet, but that will be simple as no O-ring groove is required....

Bob

rsterne · Moderator

Now that I've gone and machined the breech, Gippeto goes and tells me that wasn't necessary.... The "land" between the O-ring groove and the end of the barrel is about 0.050".... You shorten the barrel that much and then capture the O-ring between the forward side of the groove and the breech.... Should work perfectly.... Rolling Eyes

Bob