Air Gun Home :: View topic - Repeating Breech for 22XX using 850 Magazine

rsterne · Moderator

I've been working on this ever since I finished my RWS/Hammerli 850.... I liked the 850 magazines and wondered if I could make a breech for a 22XX that would use them.... I have a RIM (Rotary Indexing Magazine) and mount currently on my 2260 PCP Carbine Grouse Gun and while it functions flawlessy on the bench, when you hold the gun at odd attitudes it occasionally jams.... When it does it is a b!tch to clear.... and I figure that come hunting season it will undoubtedly cost me a Grouse so I need something that is foolproof.... Rolling Eyes

The 850 indexes the magazine when you function the bolt.... but I figured that was too difficult for my first attempt at making a breech.... I don't find indexing the RIM by hand a problem, so I went the manually indexed route.... The breech is machined from a piece of 3/4" x 1" aluminum bar stock 6 1/4" long.... It is virtually the same size as a Crosman steel breech except about 1/8" deeper to allow room for the magazine below the barrel line.... Instead of positioning the magazine so that the bottom hole feeds the pellet I used a hole at 45*.... this enabled me to leave the right side of the breech intact for structural strength while machining the magazine notch nearly down to the main tube recess.... An added benefit of this approach is that the breech is basically the same height above the barrel as a Crosman steel breech, and the magazine sits so low I can use medium height scope mounts.... The RIM requires high mounts.... Evil or Very Mad

The magazine is held in place with a brass pin that slides in a slot milled in the left side of the breech and it and the spring are held in place with a cover plate.... You pull the pin ahead to remove and replace the magazine.... The indexing mechanism is a bit Rube Goldberg but it works.... I have a small piece of nylon plastic bolted to the side of the breech that rubs on the tiny indexing ratchet on the magazine.... It doesn't locate the magazine perfectly every time, but it is close enough that the probe on the bolt always enters the hole in the magazine and the taper on the bolt moves the magazine until it all lines up to feed the pellet.... I used a stock Crosman bolt with a 0.15" long extended probe and the front 1/2" of the bolt turned down a bit so that it slides through the 6mm holes in the magazine.... Wink

I haven't mounted it on a gun yet, but it seems to function perfectly.... Once the magazine is loaded with pellets, you pull the bolt back, slide the magazine pin ahead and drop in the magazine and release the pin.... Moving the bolt forward loads the first pellet.... To reload, you pull back the bolt, and using your left thumb, rotate the magazine clockwise one notch, then push to bolt home to load the next pellet.... When you can't see any pellets in the magazine, you have either 1 or 2 remaining.... Since this is intended for hunting, that means it's time to pull the magazine and replace it with a full one.... In case you aren't aware, the pellets in the magazine are retained by a rubber O-ring in a groove around the outside.... Maximum pellet length is 10mm which is long enough for EunJin domes.... One added bonus is that you can also reload the magazine without removing it from the gun.... Cool

Before any of you ask.... NO, I will NOT be making them for sale.... I have between 20-24 hours of machine time into it.... not including the time I spent looking at it and pondering how to work around the next problem.... Mr. Green

Bob

Lipoly · Veteran Member

Alstone · Moderator & Site Supporter

Nice one Bob! I like the idea of off setting the magazine to keep the hight down.

Al

rsterne · Moderator

Here is a photo of my completed 2260 PCP Carbine Grouse Gun.... 16 shots (2 magazaines) at 20 FPE filling to 2000 psi and shooting down to 1200....

C'mon Hunting Season.... Mr. Green

Bob