I bought some once fired brass, and resized and trimmed to length, and much to my surprise, the cases were a bit short for the chamber, and most of the cases ripped off about an inch from the base. I am using Lyman dies, and a lee shell holder. Perhaps this is where my problem came from. I took a set of feeler gauges, and kept lowering the die toward the shell holder until the rifle would just close on a reformed case, starting with a .024" gap, which would not allow the bolt to close. I wound up using a .011" gap between the die and the holder. This worked perfectly, and was simple and completely repeatable. No more split cases.
Reforming 300 win mag to 308 Norma Magnum
- Thread starter 22to45
- Start date
Did you anneal, the book answer is in the Pic below. But hey I've never done that conversion
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First off, you are choosing the wrong brass. Compare a 300 Win Mag & a 308 Norma Mag case side by side. See the difference?
Now compare a 7mm Remington Mag. case & a 308 Norma Mag case side by side. Can you tell the difference? I thought not.
If you cannot find some 308 Norma Mag. brass, grab some new 7mm Rem. Mag. brass, expand the case necks & you're good to go. No using too long brass which must be re-formed & trimmed and will result in the case neck being formed from the thicker brass from the shoulder / body. I've been doing this for over 40 years. If you can't find 7mm Rem. Mag. brass, look for some 338 Win. Mag. brass.
After Winchester brought out the .458 Win. Mag. in '56, the .338 Win. Mag. in '58, then the .264 Win. Mag. in '59, the next logical step was a short .30 calibre magnum cartridge. BUT, Norma introduced the .308 Norma Magnum in '59 along with its bigger brother the .358 Norma Magnum in '60, both of which were designed by their Chief Ballistician Nils Kvale [whose first short Magnum Belted cartridge was the 8x61 Kvale Magnum in '49], screwing up Winchester's plans to legitimize the older .30-338 Magnum wildcat. They had to go back to the drawing board, coming up with the .300 Winchester Magnum in '63. In the interim, Remington came up with the 7mm Remington Magnum in '62, thereby filling up the mid-calibre short magnum cartridges.
Now compare a 7mm Remington Mag. case & a 308 Norma Mag case side by side. Can you tell the difference? I thought not.
If you cannot find some 308 Norma Mag. brass, grab some new 7mm Rem. Mag. brass, expand the case necks & you're good to go. No using too long brass which must be re-formed & trimmed and will result in the case neck being formed from the thicker brass from the shoulder / body. I've been doing this for over 40 years. If you can't find 7mm Rem. Mag. brass, look for some 338 Win. Mag. brass.
After Winchester brought out the .458 Win. Mag. in '56, the .338 Win. Mag. in '58, then the .264 Win. Mag. in '59, the next logical step was a short .30 calibre magnum cartridge. BUT, Norma introduced the .308 Norma Magnum in '59 along with its bigger brother the .358 Norma Magnum in '60, both of which were designed by their Chief Ballistician Nils Kvale [whose first short Magnum Belted cartridge was the 8x61 Kvale Magnum in '49], screwing up Winchester's plans to legitimize the older .30-338 Magnum wildcat. They had to go back to the drawing board, coming up with the .300 Winchester Magnum in '63. In the interim, Remington came up with the 7mm Remington Magnum in '62, thereby filling up the mid-calibre short magnum cartridges.
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- Location
- Western Manitoba
I have never done that conversion, but I have converted 7mm Rem Mag into 7x61 S&H. I never did any case annealing to previously fired cases. If you have a "gap" between your shell holder and the die that you are using, the die and the rifle chamber are not "matched". Why that bolt closing thing is so important - more or less throw away the original die maker's instructions - you are NOT likely making SAAMI standard stuff - either your rifle chamber no longer needs or wants that, or the die that you are using was not cut to SAAMI dimensions.
- Location
- Western Manitoba
As it happens, I was able to find examples of each of the cases mentioned above - picture below:
An unfired Norma brand 300 Win Mag case on left. Then an unfired Norma brand 308 Norma Magnum. Then a previously fired "FC" 7 mm Rem Mag. Then a new, unfired W-W Super brand 338 Win Mag
- Location
- Western Manitoba
I do not own a 7mm Rem Mag rifle, so I have no sizing dies for that one - although I do have 7mm Rem Mag brass. Picture of dies below:
The RCBS and Bonanza dies boxes have got RCBS #4 shell holders in them. The Lee die box has got a Lee #5 shell holder in it.
The RCBS and Bonanza dies boxes have got RCBS #4 shell holders in them. The Lee die box has got a Lee #5 shell holder in it.
Can use a trim die to form from 300wm brass, but as was mentioned, neck turning will be needed and care taken to not dimple the new shoulder too much.
Its energy intensive, but useful to do with good brass like Lapua.
Just don't get it confused later...
Its energy intensive, but useful to do with good brass like Lapua.
Just don't get it confused later...
I just necked down 338 win mag, easy one pass through the sizing die. Once I had enough actual 308 NM brass, I kept the converted 338 for use in the 30-338 I had. - dan
All the replies were interesting. Yes I am fitting the brass to the chamber of the rifle I have. I have read recently that one manufacturer does not recommend using shell holders from another brand with their dies. This of course could just be marketing, or shell holder thickness might actually vary. I do not intend to shoot this rifle a lot, and a set of brass that works 3 times will last me a long time. But it is nice to have my father's beloved magnum up and running.
I have mixed shell holders and dies from different makers many times. While there is a possibility of stacked clearances giving you grief, it's very unusual. - dan
I have used 7 Rem mag and 300 Win mag to form the Norma. The 7 was easy to form but slightly short which I didn’t like. I prefer the 300 mag case as I could trim to the length I wanted. I didn’t need to thin the case necks. Loads are at or near book maximum. Two loads using 165 gr and 180 gr.
