I've come across an M-S rifle (possibly a model 1925) of a mystery chambering.

Its only visible barrel markings are British "7.62mm 20 ton BNP"and a couple crowns and a 4-digit serial number. It is a double trigger gun.

It was assumed by the owner to be chambered in 30-06, but the bolt doesn't come close to closing on a 30-06 factory cartridge. The muzzle swallows a 7mm bullet with no contact.

Any idea what chambering this is likely to be?

So would 20 Ton-force be 45,000 PSI? Is the conversion linear? Sounds like 303 British? Just a wild guess.

Cheers,

Raimey
rse

also might be a 30/40 krag.

Grouse Guy,
Is the rifle's model number shown on the receiver ring? If not, which feature of the rifle causes you to believe it might be a mod.1925? It would be helpful if you posted a photo of the rifle and post photos of the original Austrian proof marks( if any)on the barrel, hidden by the stock. The 7.62mm is the bore( not groove or bullet)diameter in the British system, and is not necessarily the nominal cartridge designation. Under the Austrian system, the barrels were usually marked as to groove diameter. "Slugging" the barrel and making a chamber cast is the most positive way to ID the chambering. If the rifle is a rebarreled military rifle, it could be chambered for different cartridges that were not available as factory chamberings; a chamber cast would sort this out.
Mike

The .308 Winchester cartridge is also known as the 7.62 NATO. Is there a possibility that .308 Winchester could be the mystery caliber?

The 308 is a possibility in later models and rebarreled military actions, but I don't believe so in a mod. 1925. We need photos and chamber cast. Neither 303 nor 30-40 would be a possibility in a Schoenauer , because of the rims.
Mike

.30 Remington or .300 Savage are also possibilities.

Our best provisional assessment is that this is a gun that has been rechambered and rebored to .308 Win. in England, probably a 1903 which came from the factory as 6.5X54MS.

As soon as the stripped screw holding down the front scope base is removed, this will be confirm able.

Thanks all for your thoughts and suggestions.

Just curious, did the 30-06 round load into the magazine?

craigd's question is a consideration, I don't know if the extractor will slip over the rim of a cartridge that is not fed from the magazine in a M-S or not. An unmodified 98 Mauser bolt won't close on a cartridge that is not fed from the magazine, I'm not sure about a M-S, I don't have one "in hand" to check.
Mike