300 ultra brass from 7mm ultra?

[Eastcoastshooter375]

I have seen ample supply of 7mmRUM brass but 300 is limited. I know the 338 ultra has a shorter body, but wasn't sure about the 7RUM.

I would expect the neck thickness would be off, but how much, I'm not sure.

 

[Lefty7mmstw]

I have seen ample supply of 7mmRUM brass but 300 is limited. I know the 338 ultra has a shorter body, but wasn't sure about the 7RUM.

I would expect the neck thickness would be off, but how much, I'm not sure.

When I tired out my 7rum I went to 300 rum and necked the brass up I already had in 7 rum. I've got over 100 rounds of this brass in use and the only issue I've had at all is a couple of necks splitting on the first firing. Annealing before necking up would probably stop this. For me it was simply staving off dropping a $100 bill on brass. As to neck thickness, it'll be a smidgen thinner but who cares; I'm still getting .5 to .6 moa from a 9# 300 rum without a brake.

Do a 50 and see if it works for you.
BTW, Lube the inside of the necks a bit so they neck up more evenly.

 

[Eastcoastshooter375]

Lefty, I will definitely give it a try. I've got close to 120 emptys that are approaching retirement, but have 40-60 1x fired that should last a while. Just thought I might try necking up 7RUM in case 300RUM brass becomes even harder to find. Wanting to get things back in my "comfort zone" . Now if I could figure out how to turn 150gr noslers into 230gr Bergers.

 

[Lefty7mmstw]

I'm wishing for a few more 225 gr hornady pills too bud. Lucky the 180 and 190 hornady pills fly true also and I've got a few hundred each of those.

 

[Stavi300RUM]

Are you saying that a person could run 7mm RUM brass through their FL 300 RUM die and it'll do? What all needs to be done to do this? I'm wanting to use up my 7 RUM brass.

 

[Doublezranch]

Yes. It would be a perfect way to use up your 7 RUM brass and fill the need for your 300 RUM brass shortage. Run your 7 brass through the 300 fl die and your ready to roll.

 

[Erik Kiser]

It's essentially the same thing guys do with 300 Ultra brass to make 338 Edge although the 7mm to 300 up size isn't quite as much as making the Edge brass