Sorry to say, even by any official definition, the 45-70 is "not" straight walled. I know in Delaware the 45-70 is not considered a straight walled cartridge.
Here is the definition of what are considered legal handgun cartridges for hunting in Delaware from their Division of Wildlife web site:
Legal handguns are limited to revolvers and single shot pistols with a minimum barrel length of 5.75 inches and a maximum length of 12.5 inches and chambered for and using straight-
wall handgun ammunition in .357, .41 caliber, .41 magnum, .44 caliber, .44 magnum, .45 caliber, .454 caliber, .480 caliber or .50 caliber and using open sights, metallic/mechanical, optical or telescopic sights. Since the .460 casull is a .45 caliber, it is legal under the existing handgun legislation.
I'm going to try to get me a ".460 casull" that is a ".45 caliber." According to their definition, a 38 Special would be a legal hunting handgun but I doubt they know that. I believe there are some obscure and more gutless cartridges that would comply with their regs by their definition. They also list a ".41 magnum" and a ".41 caliber" as legal weapons. Then there is the ".44 caliber" and the ".44 magnum" so the 44 Special should be OK. Then the geniuses go on to mention the ".45 caliber" and the ".454 caliber" handguns. Whoever wrote this doesn't know their *** from a hole in the ground. If you wish to go by the definition espoused by people that don't know the difference between bore diameter and cartridge for your definition of what is a straight walled cartridge, more power to you.
The 45-70, by the way, wouldn't be legal there since their is no "handgun ammunition" available for it. Of course, if I have a 45-70 handgun and have ammunition for it couldn't I legitimately call it handgun ammunition?
According to the 7th Edition Hornady Handbook of Cartridge Reloading, "the 458 Winchester Magnum...is a straight-walled cartridge." Now, if you compare the dimensions of the 45-70 Government cartridge to those of the 458 Winchester Magnum cartridge you will find that in the 45-70 the head of the case measures .504 inches and the mouth .480 inches. In the 458 Win. Mag., the head of the case measures .513 inches and the mouth .481 inches. Therefore, if the the 458 Win. Mag. is a straight-walled cartridge according to an official source that actually has a knowledge of firearms and cartridges, the 45-70 certainly is as well. Straight-walled means the wall is straight without a shoulder as in a bottlenecked cartridge.
I'm still looking but haven't been able to find any cartridge data for the 460 casull.