Want to build a 458 rifle

[akshooter]

I'm want to build a 458 caliber hunting rifle. I'm considering using one of the ultramag cases and necking it up to 458.
 
There are several existing 458 wildcats based on this case diameter such as the 450 Howell, 458 African Express, and the 450 Vincent Long to name a few.
 
My concern is that necking up a 404 Jeffrey diameter case to 458 doesn't leave much of a shoulder for headspace.
 
Have any of you out there had any experience with this type cartridge / wildcat or know anyone that has?

[JJ Kelly]

460 Weatherby or 450 Dakota (450 Rigby) are the biggest .458's. I use
a .458 wm in a Ruger #1, it is enough for me. My friend has a #1 in .458
Lott and 150-200 fps more. Other studies with .458 caliber guns show
best results with a 500 gr. bullet is about 2400 fps. The above cartidges
get close to 2700 fps. max. I mostly use 400 gr bullets at 2200 fps in my
.458 WM, I have only shot hogs, biggest about 300lb, they go right down.
 
 

[Nobade]

Accurate Reloading has pictures of the cartridge you are thinking about as well as loading data. It is a very good one, has plenty of shoulder and power wise is right in there with the 460 Wby. Just a straight neckup of the 375 Ultramag with no other changes. I have been thinking about doing one myself, but I have a 450 Ackley reamer and would have to buy the reamer for the 458 RUM so I think I'll go with the Ackley. Besides the extra 100 fps isn't needed anyway, just makes it kick that much harder.

[JJ Kelly]

Nobade: How does the .458 RUM headspace if there is no shoulder, rim
or belt? Also I would not use any case with re-bated rim because you
tend to get bolt over base malfuctions and in a rifle being used for big
stuff, not a good idea.

[Nobade]

The 45 caliber version has plenty of shoulder. Looks like an overgrown 35 Whelen. It is the one in the middle, also called the 450 Vincent Long when made from 404 cases instead of Ultramag cases.

If you make an Ultramag case straight it makes a 50 caliber cartridge. There is one called the 50 Razorback, but it headspaces on the case mouth. That's a lot trickier than a 45 version.

[JJ Kelly]

Still don't like re-bated rim. I do like .458 bullets, there big enough and not
crazy money. Another cartridge I like in .458 dia. is 460 A-sq short, which
is a shortened 460 Weatherby case, same length as .458 wm. If we want to
go .50 cal, I like the 495 A-sq, again .460 weatherby case opened up straight,
no neck, headspace on belt, case 2.8" long, Don't have a reason to have one.
What ever the cartridge you are going to use, easy to get brass is one less
headach.

[corbanzo]

I think this is what you are looking for. 


http://www.z-hat.com/Ultracat.htm