I was considering a new wild cat the other night but I want to make sure that before I go through the trouble of even drafting up the case that its not something that has already been done.

I was thinking of using a 300 ultra mag case and cutting it down to fit in a 30-06 action and then necking it to accept a .430 dia bullet.

A shooting buddy says I should use a .378 weatherby case but I want to make sure I can still use a standard action. The idea would be to convert a Winchester M70 for this. The purpose would be to not only be able to name my own cartridge but to also have a sweet 44 magnum rifle for moose up here and hogs in the lower 48 not to mention blowing the crap out of what ever I want on the range.

Look instead at the B&M cartridges. Using that case the bullet will go too fast for pistol bullets so you might as well use a diameter better suited for hunting.

I have and they make some awesome stuff but one of my bucket list goals is to attempt some sort of wildcat I can call my own. You are right about velocities. I figured I would have to use heavy .430 dia bullets 300+gr I was wondering if anything from Swift would work like their bonded A frames. Of course it wouldn't kill me if something like this lead me into swaging my own bullets so I could obtain 400+gr ones.

What about 404 cartridges based on a shortened ultramag case?

404 Dakota, basically?

If you want to use pistol bullets AND rifle bullets, look at .410". 41 mag pistol bullets and premium bullets meant for the 450/400, although there are .408-.411 diameter bullets in that particular bore.

Yeah that's my problem there really isn't anything that hasn't been tried unless it's something stupid-overbore. If money was no object I would see what could be done with a 378 case if you could make the base of case the diameter of the belt.

I will have to look at .410

I think its a fun idea to be able to use a big bore for unintended used like on varmints with light for caliber bullets. For example I size 200gr .375's to .366 for my 9.3x62mm and get around 2700 fps. Kind of like getting hit with a 155mm for the gopher. lol

why mess with perfection we have the  .22lr, 5.56, 7.62,.338, .357, .45

Because it's a bucket list thing to want to name a cartridge.

The likelihood of you coming up with something new is extremely remote, approximately on par with FBHO and HRC deciding to tell the truth, the whole truth, and nothing but the truth.  
I'd check Cartridges of the World and the Handloader's Guide to Cartridge Conversions if you want to be sure, but wildcatting has been going on pretty much since the birth of metallic cartridges.  
Since you're really just looking for a "legacy"cartridge, simply change one dimension of the (assuredly already existing) cartridge case, and call it your own. That's pretty much what 80% of the wildcatters did.

Conceptually, the .430 M1garand_man sounds like a fine "woods" cartridge, something that would be at home in a short, handy rifle. With heavy (long) bullets, you'll run into the same problem that hampered so many short-action cartridges (like the .350 RemMag): mag box length forces you to deep-seat the bullet and limits velocity. Cut that case to intermediate length (like the 7x57 Mauser), and you can take full advantage of the .30-06 length action.

Unless something has changed to M 70, is mid-lenght action.  Same as a M-98, M-700, Springfield, etc .........

You could use a .378 case, maybe turn off the belt and or rebate the rim to fit the bolt face.  Then have reamers and dies made.  
I'd advise a Cobon as well..Gun Digest had an article written by a guy swaged .452's FMJ's for his .404 Jeffery (.423 ) to shoot wood chucks

what is that a 32 necked to 22?