I was reading the information provided at the following thread, regarding fire-forming.
http://noslerreloading.com/phpBB2/viewtopic.php?t=4191&highlight=fireforming

And by the two completely different versions I'm finding, I'm lost as to what would be the proper way, and most importantly, the safest way to doing such a procedure?

What initial plans I had on the drawing board is that since neither Nosler nor Lapua offer .338 RUM brass. To take the .300 RUM Nosler offers, and use a .338 RUM sizing die with expander ball.

One side of me says it shouldn't be too difficult since I would only be moving the inside radius of the case neck approx. fifteen thousand of an inch. But the other side has the concern that doing so, would just crush the case.

Would I be able to get away with using something like an sizing die with expander ball to size up, or would I be better off to fire form the cases?

And where I've read two completely different opinions regarding fire forming, which would be the better option?

The 300RUM brass is 2.850" and the 338RUM is 2.760". With the 338RUM being shorter, I just don't think you can shorted a 300RUM case that much and not ruin it. I am just guessing here, maybe those with more experience will chime in and help you out.

Sizing up is the easy part. I would use a tapered expander and lube the inside of the case necks. I just stick the necks in Imperial sizing wax, give the case a quick turn and remove the case. Then expand. Remove the Imperial with a good solvent and a Q-Tip. I will have to look at the 300RUM case and measure the length of the neck, trim one to length of the 338 to see how much neck remains. Then look at the location of the shoulder of each. That should solve the question.Rick.

I've never formed / altered a case once in my life....but agreeing with Rich on this one. Others will certianly have more input on this, but if I remember correctly, the 338 edge is based off the .300RUM case due to the different specs.
The taper on the .338RUM from the case body begins at 2.296 in where the taper on the .300RUM begins @ 2.387 in.
I belive your dimensions are going to be too long with the .300RUM case ??

Isn't those dimensions SAAMI Max?

But doing more reading...................

Alot of manufactures are still calling it 338-300. Though I don't see what the difference is.

My plans are to build this one from the action up. I was hoping to be able to stick with either a Savage or Remington action.

But if that option is out, I'll have to look in to what BAT has to offer. Though if I do have to go that route, I might as well go with .338 Lapua

Yes they are, but as already mentioned, by the time you trim down a 300RUM cas to 338RUM dimensions, you may not have enough of a neck to properly hold the bullet.

My advice is just buy some Remington 338RUM brass. I would only consider fire-forming for a wildcat caliber where the dimensions are identical.

One problem sizing up you may have a thicker neck also get the dreaded donut you just don't know what the shoulder thickness is that will be part of the neck.

You might want to try this site those guys are playing with different 338 type mag and they have some gunsmith that post there also that can help out what the best brass to use. http://www.longrangehunting.com

I expanded a 300Rum to 338 without a problem, the OAL shorten by 0.005". The biggest problem would be the location of the existing shoulder. I don't have 338Rum dies so wasn't able to size the case to 338 dimentions. Doing so could collapse the case. Form dies might be able to move the shoulder back. Remove your expander/depriming stem from your FL die, lube a case and give it a try. Don't worry about a donut, that is easily handled. Can't say for sure how long the neck would be after FL sizing, you might have to ream or turn the neck. A lot of bench time.Rick.

When necking up you will have thinner necks, necking down will be thicker necks.

Thanks for correcting me!


Last time I checked the body length on the 300RUM is 2.387" and the body length on the 338RUM is 2.296" so I would assume you would be sizing that part of the case (I called that sizing up just how I do things)) and the OAL 338RUM case is 2.760" vs 2.850" for the 300RUM.


Till the 300RUM case is formed how much will have to be trimmed I cann't answer. Since the neck on the 300RUM length is .246" vs .330" for the 338RUM some of the shoulders will have to form into the neck length for the 338RUM. If the shoulder thickness is the same all the length of the neck that would be nice .

Like I said in my first post " you may have a thicker neck also get the dreaded donut you just don't know what the shoulder thickness is that will be part of the neck". 6ppcar, I figured that would handle the part about thicker neck and necking down but what do I know. I don't have any Nolser 300RUM brass if someone has some and formed 338RUM brass they may have the answer.

Having a 300RUM rifle and play with varies wildcats I did mess with some Rem 300RUM brass and the shoulder thickness on the brass I have is .017" + - and my neck thickness runs .0145" to .0155".

I have had good luck with R-P 338 RUM brass so I haven't attempted to reform better 300 RUM brass.

If Nosler ever offers 338 RUM brass, I will be all over it.
Nosler, when can we expect 338 RUM brass?

JD338

Well I can just hear the toilet flushing on this idea now.



I was hoping to stay away from R-P brass for the time beings since I'm still having some complications as a result of the CTR surgery I had back in July.

I have one case each in their Ni plated stuff sitting around for my 22-250, 25-05, and 300 Win Mag. because of this.

Hand loading in general don't bother me, its the case prepping.

I'm with you on this one, if they had it I would have already ordered it. And this question would have never crossed my mind.

A seasonal run of 338 RUM, here and there would be nice.

Other wise I would go with .338 Lapua unfortunately the case head its too big for either a Savage or 700 action to safely accommodate.

I'd suggest getting your chamber opened up to a 338 edge. It's just a 300 Rum necked up to 338 without moving the shoulder. A side benefit is that it is ballistically superior to the 338 RUM. That is my opinion, however, I've never used a 338 Edge. There is one or two guys that have them here.

JT.