375 Remington Ultra Magnum necked up to 50 caliber (.510)

[375rifleman]

Hello, I am looking for any and all information regarding the 375 RUM necked up to 50 caliber (.510) wildcat rifle cartridge. Thanks in advance for any thoughts, opinions, or answers.

 

[Buckskinner]

I dunno about that cat... Since the 404 Jeffry only has a 9 degree shoulder the neck would actually be larger than the case itself...

 

[THEIS]

Hello,

Have you looked at any of the 500MDM, 50 B&M or 50 B&M Super Short wildcats to see if they meet what you are anticipating your needs to be?

THEIS

 

[J E Custom]

Hello, I am looking for any and all information regarding the 375 RUM necked up to 50 caliber (.510) wildcat rifle cartridge. Thanks in advance for any thoughts, opinions, or answers.

The RUM case would just barely work for a .510 dia bullet because the case body at the body shoulder junction measures .525 and for all practical purposes the shoulder would be non existent
making head spacing marginal. you could AI the case and go to .535 with less body taper and end up with a shoulder of 12.5 thousandths (Still very little).

I looked into using the 50, 45, and the 416 and came away with the 416 as my choice of a boomer for many reasons. I have never regretted my choice and It is one of my most accurate rifles, with the best group @ 100 yards being .034 thousandths 3 shot group.(34 thousandths larger that the bullet Diameter with a 400 grain bullet @ 2700 ft sec for all the power I need).

Here is the rifle and some of the earlier specs. and pictures.

http://www.longrangehunting.com/forums/f28/416-buff-21003/

J E CUSTOM

 

[IdahoCTD]

You forgot the neck thickness added to the bullet OD of .510. That makes the loaded round .535" or more so you would have to headspace it from the end of the case like a pistol case.

 

[375rifleman]

Basically I'm wanting to send a 750gr Hornady A-Max to 1800fps-2000fps range, out of the shortest possible barrel length without getting into SBR's so 16"-20" barrel length as cost efficienct (using as common components as possible) as possible. Maybe I should look into the WSM, WSSM based cartridges, or even the 338 Lapua cartridge as a base cartridge. Thanks in advance for any thoughts, opinions, or answers.

 

[IdahoCTD]

Anything with a Lapua bolt face would be easier so you'd have at least some shoulder to headspace against. A 338 Norma necked up and blown out would work.

 

[J E Custom]

Basically I'm wanting to send a 750gr Hornady A-Max to 1800fps-2000fps range, out of the shortest possible barrel length without getting into SBR's so 16"-20" barrel length as cost efficienct (using as common components as possible) as possible. Maybe I should look into the WSM, WSSM based cartridges, or even the 338 Lapua cartridge as a base cartridge. Thanks in advance for any thoughts, opinions, or answers.

You might look at the 378 Weatherby class of cases (378 ,416 and 460 because they are bigger and have a belt to head space on. with this case you have a very strong case and head space is not a problem. if you don't like belted cases have the reamer slightly longer than the parent case and after fire forming, size the case less than full length and you have a beltless case that head spaces on the shoulder.

Here is an example

http://www.longrangehunting.com/forums/f19/375-zayne-175302/

J E CUSTOM

 

[Bravo 4]

375,
I know you have been chasing this for years now. So I tried to make you a dummy round today to no avail. I just couldn't get a .338 Edge case to hold up to such a large jump. The shoulders caved in, even after annealing them (even tried with necks fresh off the flame). This would require multiple steps up in caliber, that I don't have the dies for.
You will not reach your velocity goals with a short mag case. The RUM cases or bigger are needed. Even though mine is a shortened RUM case, it still has more room than the shorter cases.
As stated before, my rifle with a 16" barrel may reach your minimum target velocity with the 750 Amax. I pushed it to 1750 fps before I stopped, and didn't see pressure signs. Maybe if you played with a different powder and with a slightly longer barrel you could break the 1800 threshold. Or go with a bigger case so as not to have to push it.
It's a fun rifle (especially suppressed), CEB sent me some of their 350 grain Handgun Raptors last month to try and see what they will handle as far as velocity and tight twist (rpm's). Need to shoot a hog/deer/coyote to test terminal performance. These things have a giant hollow point with pre-scribed petals that come off. I bet it'll be nasty!
And yes it does headspace on the case mouth, works fine as long as you have your cases trimmed to the right length.

 

[Bravo 4]

Also, if you want a couple of dummy rounds to have your own reamer and go/no-go gauges made then just let me know. This is for a shorter (2.38) case.

Just my experience as well, it took PTG more than one try to get it the way I wanted. They didn't even use dummy rounds the first attempt and made me what is basically a full length .50 MDM reamer and gauges. Then I had to pay them to get others made, overall took about 6 months to get the reamer I wanted from the start.

Speaking of .50 MDM cases, if you get your hands on a few I can neck them up to .510 and make dummies to see if they would work.

 

[375rifleman]

Thank you everybody for your comments. Bravo 4 I forgot what base Cartridge your 50 started out with, but do you think that possibly a full length RUM case would work ? Maybe Ackley Improve the case first so that there's more neck to work with I don't know. I'd really like to be more in the middle of my desired 1800fps-2000fps range.

 

[Deleted member 46119]

What Bravo 4 said.

You can use a RUM case. It's rough to get them expanded all they way without crushing.

I haven't tried it with a pure 404 Jeffry case. That would work.

Taking a a RUM case off at the shoulder then expanding would be less stress and achieve your velocity goals.

 

[IdahoCTD]

Sometimes it's easier to anneal and fire them with bullseye and a cotton plug but in this case you don't have a way to hold the case against the bolt face to do so unless you build a .45 caliber to fireform and then neck them up. If the case capacity is enough, cutting them off at the shoulder would be the best approach.

BTW you can buy a Hornady neck die and then buy the expander balls straight from Hornady for all the different calibers. So you can step up as gradual as 1 caliber at a time.

 

[Bravo 4]

I use the longer RUM cases (just not .338 RUM as its shorter) and chop them off at the shoulder. A .510 cal bullet will load right into it. It is a little longer than a .50 Alaskan case (which is 2.1") and the case dimensions are so close that I use Alaskan dies.
The .404 Jeffery case is a good idea to start.
Here's one of my loaded rounds with a 750 Amax: