Can I reform 300 WM brass for 7mm RM

[gamestalker]

I got handed a bunch of 300 wm once fired brass a while back and have been trying to figure out what to use it for. The only high power I have that is belted is the 7mm RM. Obviously the 300 WM brass is longer to the shoulder than 7 mag. is.

My question is what do I need to do to make it happen, if it is even an option?

 

[Striker Fired]

It looks like you would have to trim about .1 off the .300's and run them through a & RM sizer die.Belt and case head is all the same on the outside.

 

[helotaxi]

Why? The 7mm RM brass is common enough that it's not like you're stuck doing this to keep a rifle shooting. Have you considered selling the .300 brass or trading it for what you want?

Maybe it's just me, but I have issues with having ammo around that has the wrong headstamp. I've formed all my .300BLK and 6x45 brass from 5.56 brass (nothing more than the brand and year stamped on the head) to eliminate any confusion over what I've got. Few better ways to ruin you day than trying to shoot the wrong ammo in a gun. Mis-marked cases only increase the chances of that happening.

 

[LoonWulf]

Im with Helotaxi on this, trade it to some one or sell it if possible. If you MUST form them to 7mm, then i would check them very carefully after forming. You may end up with necks that need turning, and you may also need to anneal the cases. Ive got some spare .300 brass laying around, later today i might give it a try to see what happens, Ill let you know.

 

[gamestalker]

Thanks Loonwolf!
I have been enjoying all aspects of this hobby for 30+ yrs. and have no issue with turning necks, or performing any other steps for that matter. I would really like to give it a try just for the fun and experience. So any suggestions would be greatly appreciated.

I do realize it's not a rare cartridge and is hardly worth the time and effort to most, but I really don't know anyone that would buy or trade it for some 7 mag. brass.

 

[LoonWulf]

Sorry to take so long to reply, I got busy and forgot LOL.

Anyway, I gave it a try with miniumum prep work.

cut .130ish off the once fired .300 case, and ran it thru my full length 7mm die. Came out fine, except i have obvious weak spots on the shoulder, im going to make a batch of annealed cases now and try again.

Cutting .13 off takes you down to almost a perfect length to finish trim, and my necks were .311 for the 300 opposed to .309/31 for my 7mm brass.

Ill put some pictures up after i finish with the next batch.

This was done with Winchester brass for both 300 and 7mm.