It's not surprising that your 30-30 was a little short on steam if the vet wanted a neck shot. If your bull was anything like our Hereford or Charlois, those necks are like massive tree trunks. If I had to put a cow/steer/etc. down, it was one through the brain, but given your vet's instructions, you were in a bit of a bind, I'd say. Yes, a 400 grain 45-70 flat nose would have broken that bull's neck first shot, provided you are good at estimating exactly where that spine is, buried in all that muscle. I was reading an account by a buffalo hunter the other day (fellow hunted buffalo back in the 1800's professionally, dropping about 50 per day). His spot of choice was the neck, but he used big, heavy bullets out of his black powder rifle. I shoot both the 30-30 and the 45-70 and there's no comparison when it comes to penetration .... the 400 grain, flat nose bullet at 1,400 fps is like a freight train and no bull's neck is going to stop it, so better make sure there's nothing important standing behind the bull when you use a 45-70. I'd imagine, however, that it isn't every day that a vet asks for a neck shot. If you could get the old boy in a chute, you could have simply opened up its carotid with a knife, then given him a poke to get out quick so he didn't pass out in the chute (else you'd be dragging him out with a tractor). But I'm guessing that wasn't practical at the location you were at. The 30-30 is a good round, but not for 2,000 pound animals.