Will this Work?

[Shoalwater]

I have an idea rolling around in my head for and ELR cartridge. I want to take a 300RUM and push the shoulder, neck, OAL, etc., back by .200". This would give you a case OAL of 2.650, a mini 300rum if you will. All the same specs except shortened by .200". I would also probably straighten the taper out to about 10 to 15 thousandths as well. It would yield a case with about 105gr capacity give or take and you would be able to seat the 230gr Bergers way out and still fit in a AICS or Accurate Mag. If my numbers are correct, it should be able to push those 230's up around 3000FPS out of a 28" bbl, making it better (drop wise) than a 338 Lapua moving a 300gr Berger Hybrid at 2850FPS, to a mile, and almost as good in the wind.

How would I go about moving the shoulder back that far? Is it even possible? My initial thought is to cut down a 300RUM FL Sizing die by .200" and just try it, but I think trying to move the shoulder that far will most likely result in a donut. Any help would be greatly appreciated.

Here are a couple of pics to help show what I am trying to do. The first is a 300RUM and the second is my shrunk down design.

 

[Gunpoor]

I have never attempted anything such as this but I think you would need to have a die maker build a set of dies to your specs and also have a chamber reamer custom made also. It would not be a cheap endeavor but would be a wildcat cartridge you could slap any name on that you want. Once you have the dies and a rifle to shoot you would need to trim 300RUM brass to the desired length and then run them through a custom forming die and probably anneal the shoulder and neck area. Load them up and fire form them to your chamber and voila, you would be ready to rock and roll with it. Way more cash and bother than I want to spend but I am glad that the wildcatters of yesteryear were more ambitious, otherwise there wouldn't be some of the commercialized cartridges that I enjoy shooting now.

 

[Lefty7mmstw]

I'd look at necking down the 338rum before I'd try to push 300 rum brass down .2 inch. That's a lot for rather strong brass; you'd likely have wrinkling and cracking at the neck even with a good anneal job. I'm thinking sort of a reverse 338 edge here. Collet 338 rum dies could be used with a 30cal collet. I believe the 338rum reamer could be used too set up correctly of course.

 

[Kansas dog shooter]

Could you do this, shorten the breech of your barrel and push the shoulder on it forward 0.200". Leaving the front of the chamber as is. You would then shorten your forming die by the same amount. Push the shoulder on the brass in short increments by backing off the die to start and bringing it back down 1/4 turn at a time. This would be about like making .222 Rem. out of .223 brass. I do that for my .222 Savage. Had a friend give me 1000 rounds of once fired .223 brass. Just my 2 cents...

 

[AZShooter]

Using a 338 RUM case was my first reaction too.

Be sure to share with us your finalized wildcat in the future!

 

[65WSM]

If you are using a Redding bushing die in .300 RUM then you could merely shorten the butt of the die by .200. The bushings are longer than your new neck design.

I like the idea. I have loaded for .300 RUM and wished for more neck to partially resize. My fellow reloaders and hunters I hang around with have decided that the 200 gr Accubonds are the favored bullet. With a case full of Retmbo in back of it.

We use Nosler .300 RUM brass. I would suspect that you will have to inside neck turn with the Forster case trimmer if you go to .338 RUM brass. I do not like to do this because I get the inside of the case all scarred up and it scratches the bullets on seating.

I have done this with a .22-250 Ackely bushing die shortened to .22-6.5 Lapua with a 40 degree shoulder.