Help! Rifle caliber I.D. - wild cat?

I

ihctractor

New member
Many years ago I inherited a highly customized Mauser 98 rifle. It came with two boxes of Norma .308 magnum brass and a set of RCBS loading dies. I assumed it was a .308 Norma magnum.
About half the brass had been hand loaded. I fired a few and they shot very nice. Now years later I decided to take this out. I bought a new box of factory .308 Norma mag. ammo. When I pulled the rifle out I was looking it over and for some reason decided to stick a bullet in the crown to see how tight it was and I was horrified to see the whole neck would go into the barrel:eek:.
So I get out the measuring tools and discover that the barrel is 8mm NOT .308! I disassembled the sizing die (which says .308 Norma) and it must have been modified because it's also 8mm.
So what is this thing??? .308 Norma mag. necked up to 8mm? What would you call it? Where do I find loading data?
I'm sure glad I didn't fire the factory stuff and have an accident!!
 
First do a chamber cast - can be done with Cerrosafe from Brownell's

First do a chamber cast - can be done with Cerrosafe from Brownell's - comes with directions. Then look at and measure the chamber casting to identify the cartridge and bore. Load data depends on what the cartridge really is.

A lead slug can be driven through the bore for bore and groove dimensions but the chamber cast can be done to include the throat.

It may be necessary to use one of the computer programs for calculated loads - going back to Homer Powley's Ballistic Sliderule for paper based calculations. It may be that data is readily available. See also LoadData on the Wolfe Publications/ Handloader Magazine web site - requires a paid subscription and also write to the NRA Dope Bag with questions - should be a paid up member of the NRA as well.

I would check first to see if the rifle is rechambered military with the bore of an 8X57 and the chamber of a .308 Norma but guessing doesn't cut it at 50,000 psi.
 
It could be any one of a number of 8mm magnum wildcat predecessors to the commercial 8mm Remington Magnum, like the 8mm Ernst, 8x62 Durham, 8mm Hollis, or 8mm PMM - all dating from the -40's, -50's & -60's.

It's tempting to think it's just a simple 8x57 rechambering with a reamed out neck on the .300 NM dies - but the .300NM was a much longer shell then the 8x57, every bit as long as a .300 Weatherby Mag.

I'd do a cerrosafe cast of both the rifle's chamber AND the sizing die.

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I'd do a chamber cast. You can also use melted crayons but they make more fragile casts and don't smell too sporty:D In a pinch they work and do give accurate casts. If you still have any of the original hand loads you can disassemble one and measure the components. It's probably a .308 Norma necked up to 8mm (which really doesn't make a lot of sense since it almost brings it back up to a .338) but that's just guessing and you want to know what it is before you fire it. A .308 Norma is basically the old 30-338 wildcat with less taper. A 30-338 is a .338 Winchester necked down to .30 caliber
 
The 308 Norma Magnum predated the 300 Winchester Magnum and the 338 Winchester Magnum by several years. Until the 338 Win Mag hit the scene, there were no .338" bullets available, there were .333" bullets designed for the 33 Winchester, which would never hold up. An 8mm wildcat might allow use of heavy bullets and use the many 8mm barrels that were available then. Maybe it could have come from Europe since many servicemen on a tour of duty would buy a rifle overseas, and an 8mm on a Norma Mag case might be a common cartridge there.

As Hawg Haggen suggests, do a chamber cast and find out what the case dimensions are, it is possible that it is a 8mm on a 308 Norma Mag, or perhaps something more exotic with different body length, or different shoulder angle, or different neck length, or whatever. Once you have it figured out, you can find a case of similar volume with similar bullet weights as a starting point for load development or rebarrel the rifle into something that is more common.
 
update.

I did some measuring of one of the original hand loads, a fired case and the chamber. As far as I can tell all the dimensions are the same as a .308 Norma Mag except necked up to 8mm. From what I've read on the net there actually was an 8mm-.308 Norma wildcat in existence. I also found out the the .338 Winchester mag has almost the exact case dimensions and that the 8mm-338 was a popular round in its day because you could simply ream out the chamber on a surplus rifle to .338 mag and leave the barrel alone. They called it "the poor mans magnum". I'm still not sure if mine is 8mm-308 or 8mm-338 and I'm not sure it even matters since the re sized dimensions are identical with the exception of 1/2 a degree difference in shoulder angle.
At this point since I'm sure this isn't a factory loading and I'm not interested in messing around with building a wildcat load I'm probably going to put it back in the safe for another 10 or 20 years as I have other stuff to shoot. I'd be interested in reaming it out to a commercially offered 8mm but from what I could find there's nothing out there that has a slightly larger case that I could use and still fit this action, plus the gun was custom built by a past family member and looks so nice that re barrelling it would be a travesty:(
 
The 308 Norma Magnum predated the 300 Winchester Magnum and the 338 Winchester Magnum by several years.
Click to expand...

The .338 Winchester came to be in 1958, the .308 Norma in 1960 and the .300 Winchester in 1963.
 
8mm/308 Norma Magnum

I have had a Brno Mauser for years that had been re-chambered to 8mm/308 Norma Magnum. The chamber has a very long leade (ala Weatherby) and the magazine has been stretched... a piece of 20 ga barrel welded to the front of the magazine. This allows a 200-gr Nosler Accubond to be seated for a LOA of 3.490". Flat-based bullets may be seated to the base of the neck for a somewhat shorter LOA.
I use 76.0 of H4831SC powder for a muzzle velocity of 3000 fps at 7400' elevation. Three-shot groups are sub 2" at 300 yds... one was 1.940". It is not maximum in my rifle, but follow the usual precautions and work up to that load or stop as pressure dictates. The barrel is a standard stepped-diameter military barrel, 23.6" long. I re-stocked it with an old Bishop "straight and plain grain stock, glass-bedded thru the chamber area and free-floated beyond. Scope is Leuplod VariVII 3-9 40mm.
I have taken Texas WT deer, Colorado mulies and elk with it, using a variety of 196-200 gr bullets. It does not "like" lighter bullets, and 220-225 gr bullets did not perform well. IMR4350 is the fastest powder I have found to work well, and the H4831SC works very well.
You have a gem. Feed it what it likes and let it run....
 
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