500 Ultra Mag?

BigUglyMan

BigUglyMan

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I know, normally I'm a crusader against über-magnums, but I've been thinking about it lately and wondered if anyone had heard of anyone necking the 300 RUM up to accept .510" bullets?
 
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This would take some doing as the OD at the shoulder is .526, and the brass thickness is about .04. So you'd have to remove some of the body taper to make this work. Furhter, this leaves no shoulder, so headspacing becomes an issue.

A 458RUM is more reasonable.
 
I think the right way to proceed would be to have the case blown out so it had no taper, thus maximize the amount of shoulder you could head space against. I think you would still end up with a .416 Rigby type shoulder, but it would be interesting. At a guess, a 570 gr. bullet would get between 2400 and 2500 fps...it would be a powerful mother!
 
BUM, you would likely have more success with headspacing using a belted magnum case or a modified Rigby. All of which have already been done.

Even when fully improved, the RUM case will not leave a lot of shoulder for this cal. Not sure how little shoulder you actually need to headspace properly.

Also, bullet selection is pretty low considering the issues with the BMG. Unless you plan on using cast bullets.

Don't laugh, a hard cast with gas check can go 2200fps quite easily which is close to the case capacity max. You can get some real heavy bullets now. 500/550 gr are easy. You might be able to dig up a 600 to 650gr too. Custom molds will make this a snap.

How about a cast 650gr spitzer w/gas check bumbling along at 2100fps? A 300wby case blown out to a straight taper would work great (well maybe not enough width, the 378 wby case would).

Jerry
 
I just played around with one of my .375 Ultra cases and my cartridge conversion software and it looks like Prosper is right - the case would end up being a straight wall arrangement even blown out, and without a belt - head spacing would be difficult, if not impossible. Looks like we'll have to make do with the Jeffery one of the A-Square rounds.
 
Ultra.jpg
 
So headspace it on the case mouth.It only has to hold position untill the primer goes off .After that the case comes back on it's own:D against the bolt face.
Rich
 
I've never seen that application used for a high pressure rifle round, just pistol rounds. If there was case stretch where could it go? The case head would be tight to the bolt face, and the case mouth would be indexed at the front of the chamber.
 
Probably because there's a better solution: Belted or rimmed cartridges. Problem solved, parent cases readily available, so the problem just goes away
 
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