Forming 338win mag

[b money]

I just bought a 338win mag and don't have any brass, but I do have some 7mm rem mag, and some 264win mag that I will never use. Is it possible to resize these to 338win mag? I'm thinking I'll have to anneal the necks, then run through a 300win mag neck sizer then through the 338 full length die. I'm hoping I won't have to turn the necks as I have no way of doing so. I bought some IMR4350 and will probably load some light loads to fire form them. At least that's my plan. Does my thought process seem reasonable?

[BK7saum]

You won't have to turn the necks when you neck up to 338.

[Vann]

I do it all the time, after forming the 7mm brass will be a hair short but it works perfectly. The easiest way to form it I found is to use the cream of wheat method, otherwise you run the chance of splitting the necks or crushing cases. Also annealing the cases will help greatly. If you don't want to fireform them, I usually open the necks up to .308 then .338.

[b money]

Great to hear. I did end up annealing one case and trying just to see. By the end it was .020 shorter then the trim to length but I think it will work. can someone refresh my memory on fire forming with cream of wheat? I've read about it before but had no use for it so I don't remember the process exactly.

[ammohead]

Put about 10 gr of unique in the case and fill with cream of wheat. You can tamp a bit to help with transporting. Carefully chamber case and with bbl pointing up....fire. No projectile needed. Maybe some TP to keep cow in place.

[b money]

Ok sounds good. Would red dot work? I have probably 10lbs of red dot that I don't really use much.

[Vann]

Yep, it'll work if I remember correctly I was using 5 to 6 grains of Red Dot. Any fast pistol/shotgun will do, just start out around 4 grains for a case as big as the 7mm and go up until you get your case blown out the way you want.

[EDG]

There is no point in fire forming. Get a tapered 7mm to .338 expander and just full length size to fit your chamber and you are ready to shoot.

[cowboybart]

I don't think you will need to fired form. might be a tad short - like you said .020". Load and shoot full tilt!

[b money]

Well I annealed all the brass and I tried a 264win mag. Necking up to 30cal was do-able, pretty tough but it went. there was a little stretching in the neck where you could tell it was a bit thin, but I kept going and ran it through the 338 die. There is a little split in that neck now. So how should I avoid this? Would fire forming help?

[Vann]

That's why I fire form mine. First I anneal them, then I run them through my 338 die without the decapping rod in it so it doesn't stretch the neck, then I fire form. This makes the neck stretch out more evenly and prevents most cases from either splitting at the neck or just crushing the neck trying to force it to open up. I can open it up straight from 7mm to 338 with my Lee dies but I usually will lose 5 to 10 out of 100 if I get in a hurry. Mostly it depends on the brand of brass and how hard it is.

[Wolfer]

I've found coating the inside of the neck with Imperial sizing die wax on a q-tip helps a lot.