I have a Mannlicher Sch. 8x 56 mann.This is a propriety cartridge no longer made. This is a commercial action with the butter knife bolt handle and rotary mag. Smooth as silk and absolutely best feeding there is. BUT again for an obsolete cartridge. I could probably scrounge some bass and dies but don't want too. Would much rather get it to a standard 8x57 so no probs with ammo etc.and use the original barrel rechambered. Can this be done? Will, if I can find one, another magazine work. OR can the existing mag be modified to take the 8x57? What can I do?

For a whole lot less money than modifying an 8x56 M/S to 8x57 Mauser, you could just make 8x56 brass for yourself.

As to whether the conversion is possible, M/S rotary magazines are reported as notoriously fickle to modify. Some folks seem to pull it off once in a while with "no sweat". Others can dump hundreds of dollars in gunsmithing hours on the magazine alone and still not have anything reliable. At $75 per hour bench time, it doesn't take long to have a real bundle tied up in such a conversion.

And if your magazine gets screwed up in a conversion attempt, just where do you plan to find another? Would be a real bitch to have a nice classic rifle with a magazine which wouldn't function any more with ANY cartridge.

Early Mannlicher-Schoenauers did not have the cartridge retaining band on the forward part of the magazine. They relied on the side walls of the reciever (and stock) to help stabilize the cartridges.

The magazines were not only designed for each cartrigde, but they were designed for a particular bullet weight and ogive.

Modifiying the rifle to reliably feed 8x57 can be a nightmare, and is not for the inexperienced gunsmith.

The magazine is the big obsticle.

See if loaded 8x57 rounds will fit and feed (at least from the mag into the chamber partially) in the unaltered rifle. It may.
Or,,they might not even fit into the mag.

M/S usually feed best with round nose bullet.

The 8x56MS has a head dia just slightly small in diameter than the 8x57Mauser.
The M/S's also have excessive headspace on many occasions.

I've seen one M08 that was simply converted by a simple chamber reaming it appeared. It worked fine.
Two other conversionss needed magazine work due to the 8x57 being slightly larger at the base and the shoulder is slightly different. I never did see those function w/ ammo.

Personally I'd leave as is. For the money invested, you can buy a set of dies (yes they are expensive) and convert a couple boxes of 8x57 and be all set for a day at the range.
Conversion will kill re-sale value. As much as it would seem to be a good thing (easily available ammo) M/S buyers like them original as possible.

The dies show up on FleaBay once in a while.
I made my cases in 8x56 with 8x57Mauser dies for a long time. Thinned the shell holder to allow the case to go deeper to push the shoulder back and allow chambering. The base needs to be turned a few .000" for the M/S proprietary dimension.
Once they would chamber, I neck sized only from there, using a 32acp seater die and the .323 expander.

Now I have a set of real dies,,still have to turn the bases using 8x57 brass though.

Ammo is avaiable @ Buffalo Arms and Old West Scrounger

I originally met my friend George the Knifemaker many years ago when he borrowed my 8x57 reamer to rechamber his 1908 M-S in 8x56. M-S rotary magazine worked fine with properly-chosen roundnose bullets, as mentioned above.

Grooves of these older 8mm rifles that I've examined have run ~0.327"-0.328" but accuracy was good anyway.
Regards, Joe

I realize you said you didn't want to reload, but FWIW, it isn't a big deal. I bought a nice 1/2 stocked MS 1908 rifle in the 70's with a Lyman 36 peep on it. Set of RCBS dies and 200 8x57 cases and I was in business. Trimed them and than ran them into the sizing die full length to set the shoulder back. Loaded them up and had one sweet carrying rifle that was a pain in the A$$ for a south paw to work the bolt on. That butter knife bolt was just near impossible to grab coming over the top with my LH. Sadly I traded it off because of that.

There's been some rechambered, but why take the chance? Time you pay for that, you could be set up and have ammo to burn.

Just my .02

Thanks fellas for the advice and suggestions. I think I'll try and see if an 8x57 round will fit in the magazine and maybe I'll get lucky as some one suggested. If not I'll just retire it to a corner. I'm not keen on cartridges I can't buy and care even less for wildcats for that reason.I tried a 7x57 but no go. As some one stated the problem appeared to be the side wall. If I don't get lucky I'm not going to spend big bucks trying to make a silk purse out of a sows ear.