.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

[Rescue35]

Nice work Bob.

[gene_sc]

SImple and sweet mod there Bob. I have a few of the Crosman steel breech's and was looking at what you are doing at one time.... I love single shot breech's personally.
Great that you showing us.
Thanks
Gene
PS... Those new Crosman .25 cal barrels ain't cheep...

[rsterne]

They are cheaper than TJ's or LWs.... although they are only 20"....

Bob

[1377x]

does the 7/16 drill bit have to be flattened like a mill bit?
great work i was just asking how this is issue could be solved

[1377x]

for $50 its cheaper than going the TJ route.once you factor in the machining would it be the economical way to go the tJ route though

[rsterne]

does the 7/16 drill bit have to be flattened like a mill bit?

Yes, it does.... HOWEVER.... 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....   

The TJ's blank would have to have the chamber, leade, ports, and crown machined.... All that is done in the MRod barrel.... plus it's beautifully polished and blued....

Bob

[ten.ring]

it's going to be nice having a crosman breach that has a good close fit to the barrel

mark

[1377x]

does the 7/16 drill bit have to be flattened like a mill bit?

Yes, it does.... HOWEVER.... 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....   

The TJ's blank would have to have the chamber, leade, ports, and crown machined.... All that is done in the MRod barrel.... plus it's beautifully polished and blued....

Bob

so it is ok to shorten the barrel .050???
will the oring be exposed?when the barrel butts up to the breech the o-ring is then sealed by the breech and the back of the barrel.
am i on the right track?
i havent taken the barrel out of the wrapper yet, still have to get a breech.someone is making custom breeches and was thinking of asking them to make me a breech for a 22xx/disco tube that will accept a .25 marauder barrel with no modification needed
but if turning the barrel down and either cutting the extra off the barrel or the breech is easier that sounds cheaper.

[rsterne]

so it is ok to shorten the barrel .050???
will the oring be exposed?when the barrel butts up to the breech the o-ring is then sealed by the breech and the back of the barrel.
am i on the right track?

That's correct.... I haven't done it, but Al (Gippeto) says it works perfectly, and I trust his opinion....

Bob

[huklbery]

so it is ok to shorten the barrel .050???
will the oring be exposed?when the barrel butts up to the breech the o-ring is then sealed by the breech and the back of the barrel.
am i on the right track?

That's correct.... I haven't done it, but Al (Gippeto) says it works perfectly, and I trust his opinion....

Bob

Could you simply counter bore any barrel then rather than deal with a O ring grove?

[rsterne]

If you wish to shorten the barrel more, and then re-chamber it, machine a new leade, and move the transfer port, you could do that and then use an O-ring on the bolt to seal the breech.... IMO, a lot more work and no advantage.... other than that the forward notch on the top of the barrel would then be hidden inside the breech.... I have seen barrels done that way as well, and they work fine.... The barrel is shortened so that the middle notch on the top lines up with the set-screw in the Crosman breech....

Bob

[1377x]

i like the sounds of gippeto's or your way option better the less work the needs to be done the cheaper the transition will be
i take it tight tolerance precision is key here!

[PakProtector]

hey-Hey!!!,
Sooo...could this be done on one of the pumper pistols? I am thinking that estending the air tube/pump forward so that the storage chamber is larger and the pump arm is longer would make for a very neat carbine that could then be tuned to deliver two shots. Or am I smoaking crack?

Mod the breech as shown, and machine a new, longer tube with a longer valve stuck inside sound about right? On the pumpers the valve and storage chamber is one piece, yes?
cheers,
Douglas

[rsterne]

You would need a longer/larger valve for a .25.... The 13XX valve is about the right size for a .177, even a .22 cal will benefit from a larger valve.... The valve is a separate piece inside the tube, just like on a 22XX of Disco (but smaller diameter).... A 13XX valve is only about 1.6cc.... the one in a Benji 392 is about twice that.... I plan on 5-6 cc for my .25 cal....

Bob

[Bill G]

Bob,

Your saying that the internal volume of the valve it 1.6cc?  Is that before the poppet?

Bill

[rsterne]

Yes, a 13XX valve is only about 1.6 cc internal volume.... between the check valve seat and the poppet seat (including subtracting all the internal bits).... A 22XX valve with the piercing pin in place is about the same internal volume.... A Disco valve is about 3.1 cc to the rear of the gauge block (where the hole is ~1/8"), about 2.5cc not including the space between the gauge block and the valve (but including the 1/4" hole in the front half)....

Bob