.25 MRod Barrel in Crosman Steel Breech

[rsterne]

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]

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....

Bob

[AirGunEric]

I'm pretty sure someone around here who shall remain nameless also did a .25 cal barrel for a Crosman breech and the bolt they made had an o-ring on it...

[rsterne]

It can be done either way.... You can shorten the barrel, eliminating the O-ring and the transfer port, rechamber it, and use a bolt with an O-ring.... You can even machine the new transfer port to take a 22XX Crosman steel port if you wish.... The advantage to doing that is you can eliminate the notch I will have showing in front of the breech.... In addition, the middle notch on the MRod barrel ends up where the setscrew in the breech is.... No modifications need be made to the breech, either, so the barrel is a stand-alone part.... and it looks nicer when installed....

Of course then Mr. Smarty-Pants Al (Gippeto) comes along and shows everybody up.... He kept the internal O-ring and didn't have to mod the breech....

Bob

[SeanMP]

I like it Bob. Certainly less daunting than trimming the barrel and rechambering. I think I personally would lean towards boring the breech 0.050 deeper and retaining the captured Oring.

[rsterne]

That all depends on whether you are doing it for yourself (and don't mind "ruining," errrrrrrr, "improving" a 7/16" drill bit).... or you are supplying it to fit a stock Crosman breech.... For me it didn't matter, but I can see the advantage of Al's method.... I don't mind the notch in the top of the barrel in front of the breech.... The bolt will be dead simple, too, just a piece of 1/4" drill rod (or stainless) drilled and tapped for the bolt handle with an extended nose about 0.10" diameter....

Bob

[Gippeto]

Ah...Mr Smarty Pants is it now....Think that one could go either way there Bob. ;)

Used a 3/8" end mill to make the pocket on another barrel...works well IMO. Think I may keep doing it this way for .25 and up.

Al

[rsterne]

Used a 3/8" end mill to make the pocket on another barrel...works well IMO.

Pocket for the #010 O-ring?.... I guess you could do it with a smaller mill for .22 or .177 as well.... AFAIK, Crosman use a #009 on the .22 cal MRod and a #008 on the .177....

the "Mr. Smarty Pants" was meant as a joke/compliment.... always annoys me when I miss something that should have been obvious, only to have somebody else figure it out.... *LOL*....

Bob

[Gippeto]

Knew it was a joke Bob...was meaning that it could equally apply to you. ;)

Can't really do it this way on the .22 and .177 to fit the standard Crosman steel breech because of the 1/4" bolt bore and the need for the forcing cone on those two.

Suppose a guy could make a seperate "cup/forcing cone" to hold the o-ring and place it into the breech first...hold it in position with the barrel.... Would save having to cut the forcing cone into the barrel with the added benefit of easy bolt construction.

Might have to give that a whirl.

Going to see if the transfer port can be included....add an o-ring groove on the od of the "cup/cone/tp" to seal on a faced off barrel.......quick change barrel setup???? Maybe just put the forcing cone in the end of the barrel and leave the rest 1/4"....probe would need to be longer....something to keep me awake tonight. ;)


Al

[rsterne]

Longer probe shortens the loading port, possibly requiring longer bolt travel.... difficult to obtain on a Crosman steel breech.... but it's an elegant solution in quarter bore....

Bob