It is perfectly fine as long as you keep your shots within the range of the round. Thousands of moose and bears have been killed with that round and when it came out back in the 1800's it was the round to have. Then when Winchester offered their 1886 lever action rifle in it it turned into the best rifle out there at the time.
I took the moose in the avatar photo by my user name with a Marlin Guide gun in 45-70 and a 405 grain cast lead bullet over IMR3031 powder.
Here's a bit of the story I wrote about that hunt which is posted in the hunting stories section of this board.
'At seven feet tall near 1,000 pounds he was absolutely immense and he was staring right at me. I crouched below the hill crest and pointed frantically in moose direction whispering to John “Moose! Moose! Right There!” John crouched down and began to duck walk forward as I turned back to the moose and worked the lever on my Marlin.... Knowing that the point of impact was six inches low at 50 yards for my hundred yard zero, I put my sights on his throat and pulled the trigger. At impact the bull spun and began to lope away over the uneven ground. With a bullet in the moose I sure didn’t want to lose him in the bog (or worse down slope away from the road)! I held for the center retreating moose butt and pulled the trigger. ... I covered the 100 yards between us and saw that he was down on top of the ridge 50 yards from where my first shot had hit him.
After action report:
The first shot had broken his right shoulder just below the joint. I later recovered the bullet outside of the ribs a foot behind the shoulder.
Either my second shot or John’s shot had taken the bull six inches left of his stubby little tail, broken the left hip at the socket and passed beyond. The bullet was left behind in the gut pile so I don’t know whose shot it was, but in any case with a broken shoulder and a broken hip the moose was down. ....'
So yes indeed, the venerable 45-70 cartridge can and will still work for moose and the modern Marlin Guide gun is just the gun to do it with at close range
My middle son took his second moose, a cow, with a TC Contender 45/70 ,with a 300 gr cast bullet and a lite load of 3031, the shot broke ribs on both sides plus the off side shoulder, the bullet passed through and was not recovered, the moose ran about 40 yds.
While I was up on the mountains looking for some elk, we spotted some off in the distance. And while I was glassing these elk I couldn’t quite pick up the details of these elk because they were clear out there, and because I couldn’t keep steady enough to get a clear picture of what I was looking at. I told my brother, “I can’t really tell ‘cause I’m shaking.” He gave me the best piece of glassing advice I’ve ever been told (‘cause how many glassing tips can there really be...