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domer_pyle · Senior Member

I noticed if my scope gets bumped it changes the rifle's POI pretty dramatically at ten yards, tried 2 different scope mounts and same results.

Is this because of how the breech is held onto the gun? It doesn't seem the most secure. My barrel band is also all the way forward, would sliding it back towards the stock help this?

I can't figure this out and the excitement of a non-hold sensitive gun is really being killed by being unable to dial in precision accuracy. Any ideas would be greatly appreciated

yourdaddyjoe · Supporting Member

Float the barrel...

Drill and tap a second 8-32 set screw and you will lose the piviot point in the breech.

Shopping list:
#29 Drill Bit
8-32 Tap
1/8"x8-32 Cup Point set screw.

You need to remove the breech from the gun and the barrel from the breech.

For Safety sakes... De-gas the gun...

Remove the Stock:
Remove the safety... A bent Pick works great...
Your aming for the small wire that locks the safety in.
Big Philips screw between the guage and trigger...

Remove the barrel band.

Remove the rear breech and trigger screws. Be carefull... your hammer spring cap will pop out and the spring will fly.

This will allow the bolt to go all the way back to access the .05 hex front breech screw.

IMPORTANT
Squeeze the breech to the gas tube to compress the transfer seal when removing this screw. If the head strips... you can drive a precision screw driver into the hex socket and remove it. Best to order a new front breech screw from Crosman before starting this project... I strip them 1:5 when removing the breech.

Careful when removing the breech. the tranfer port seal lives between the breech and valve. It must go back in the way it came out.

Now you can remove the barrel set screw and seperate the barrel from the breech.

It's a good time to do your barrel crown now that you have it apart. Use the forum search function... I'm sure Slava or Al have done a post on re-crowning.

Back to the breech...

Use a center punch and dimple where you want the second set screw to prevent your #29 drill bit from wondering off center.

Drill and tap for the extra set screw.

Clean out any burrs on the inside of the breech.

When re-setting the barrel in the breech... Put your bolt in all the way, Line up the transfer port of the barrel to the breech and lock in the set screws.

The rest of the assembly is reverse of the above.

Once this is all done. the barrel is locked down in the breech... and if this mod don't take care of the problem... go back to the scope as the issue.

It's your choice to use the barrel band or not. Full Float is with out the band... but I only loose the barrel band on thicker or shrouded barrels. The idea of such a small screw to secure a breech and barrel bugs me...

domer_pyle · Senior Member

Damn, above and beyond what I was looking for but I'm definitely gonna bookmark this in case this really turns into a project. You really live up to the "Mack" part of your online handle!!!

Actually what I might do (because this will be a hunting gun that gets roughed up) is this idea I found doing a little more searching, basically putting the barrel band on right in front of the breech, and I'll keep the other one right at the end of the fill cap

http://www.network54.com/Forum/581291/thread/1301239638/Discovery+wandering+POI

Thanks a lot for that detailed write up though, that's some good info

yourdaddyjoe · Supporting Member

Thanks... no ego strokes are required... RazzDouble

I will have to say... that set up will help to keep you from developing a leak in the TX port.

The location of the front breech screw on the Disco is too far from the seal and I have heard of guys getting nasty leaks. The only cure they offered back then was to mod the valve and relocate the breech screw to the forward hole in the gas tube like any other 22xx...

domer_pyle · Senior Member

That was another part of my choice, it seemed like a good idea to pull the breech down to the air tube to prevent or avoid any type of leak. Since coming across that article I've been thinking of a way to machine a band to actually go around the front of the breech while floating the barrel. Ahh too many damn projects...

yourdaddyjoe · Supporting Member

I'm sure someone had done it... I would search around the Crosman forums and see if someone is making them.

1377x · Member

does it matter if the second breech barrel set screw is not centered?

yourdaddyjoe · Supporting Member

Preferred in the center... a small bit off and you can adjust your sights to it. The idea is to have 3 points of contact to remove any pivoting of the barrel in the breech.

Crosman barrels are not as consistent in O.D. as we would like to believe.

rsterne · Moderator

Breech Bands for the 13XX/2289 series are in production in Canada.... I gave the drawings for the one I used on my Uber-Pumper to a machinist here.... It mounts to the front of the trigger group (drilled & tapped hole required) and was necessary because I had to eliminate the front trigger group screw.... I helps locate the breech as well....

Grant Stace in New Zealand was making them for the 22XX series.... but he is difficult to deal with.... I don't know if they are still available....

I have recently designed some riser breeches both single shot and to utilize the MRod magazines.... These have a band around the Main Tube near the front of the breech to attach it and eliminate the small screw under the bolt.... When they are in production I will let everyone know.... Again, they will be made in Canada.... and they may include an integral shroud mount....

Bob

yourdaddyjoe · Supporting Member

I've been eyeballing a Crosmods breech... But... it still uses the small front breech screw..

Details Bob... I need details...