Choked bore

[yamoon]

I slugged a 8x57 98Mauser sporter today, the lands and grooves are sharp and strong. The slug measures .321, so is it a choked barrel? Were choked rifle barrels common in Germany? I am trying to decide if it is a .323 bore or not.
thanks Mike

[Axel E]

No, there were no "choke bore" rifle barrels made in Germany. But the current min/max bore and bullet dimensions became mandatory in 1940 only:
8x57I: land min 7.80 = .307", groove min. 8.07 = .318, bullet max. 8.09 = .319"
8x57IS: land min. 7.89 = .311, groove min. 8.20 = .323, bullet max. 8.22 = .324"
Before 1940, gun- and barrelmakers could use dimensions they thought to be best for a given load. If the gun stood proof, it was ok. There was no clearcut distinction between I and S bore barrels. It was a well known fact, found by the Austrian military in WW1 and others, much later confirmed by P.O.Ackley: The bore diameters of the barrel are not critical. It's the diameters of the neck and throat of the chamber that cause trouble. As not only the bullet of a S cartridge, but the case neck too is .005" larger than that of an I one, an 8x57IS cartridge wedged into a minimum 8x57I chamber can not expand and release the bullet. This causes excessive pressure, not the tight bore. In the 1920s and 30s the Mauser factory bored their sporting rifle barrels to I specifications, but chambered them with S neck and throat dimensions, "so S loads may be used too". Other gunmakers rifled their barrels to compromise .320 - .321" groove diameters intentionally, like your's . So you have to check just the chamber dimension: Shoot an emasculated American factory SAAMI specification "8mm Mauser" load in your rifle. If a S, .323" bullet slips in and out of the fired case with just finger pressure, you may use all full power, CIP specification "8x57IS" labeled loads too

[yamoon]

Thanks Axel
I will check the chamber.
Mike

[yamoon]

Could I fire one of my loaded .318 8x57 rounds to check the throat or would I get gas escaping into the action?
Mike

[mike ford]

You can fire one of your .318 loaded rounds , they would be safe in both 8x57I and IS. The neck should expand and mostly seal off the gas. You don't just have a choice of .318" and .323" bullets. You may also find that a .323" bullet won't enter the neck of a fired case, but a .321" 32 Win. Special one will. The new 165gr .321" Flex Tip bullets seem to be enjoying good press and would be worth a try.
Mike

[yamoon]

Thanks Mike