"Homicide Hank" Armstrong would also be acceptable but when you look at him and Greb at their best weight class Armstrong had more thunder, as Armstrong went up to fight bigger men he really used the volume.
From what I know about Greb all his success came from volume punching while Armstrong had a lot of his success through using volume. I don't think you can go wrong either way but that is why I rate Greb over Armstrong in term of volume punching.
Harry "The Pittsburg Windmill" Greb is probably the greatest volume puncher ever, couldn't punch for **** but by using his windmill style (hence the nickname) of constantly throwing punching he arguably is the best fighter ever based off who he beat.
In the history of boxing... people seem to forget... Paul Williams. Pacman is a monster but I think putting him down as the best offensive fighter, is a little bit of nut hugging
Prime Chavez is the best I've seen in my lifetime, Calzaghe deserves a mention. Salvador Sanchez, Ray Mancini, Aaron Pryor were also relentless punchers as well when I was a kid.
The first thing that came to mind when I saw this thread was Calzaghe, he could throw constant combinations for 12 rounds like it was nobody's business.
Chavez Sr comes to mind, talk of Armstrong of course, Pryor, Leonard at times, Duran...how has no one mentioned Duran??
Going a little further back in history, watch old clips of Dempsey, that man punched hard and he punched often. Talking of heavyweight volume punchers, Tyson would have to be up there, in his initial run as champion.
In recent memory I'd put in Pacquiao, the greatest offensive fighter since a prime Duran and a massive volume puncher too.
If we're honest, Joe Calzaghe. His constant volume and pressure was perplexing. If you've ever boxed, you know that throwing like that for 12 rounds is unthinkable for most people.