They were designed to be carried in tanks for crew weapons. Soldiers like them because it knocked people down if you were close enough to them. My dad said they were good for clearing trees of snipers.
They were still a crew served weapon carried in M60A3s in 1984 in my battalion.
Always thought they were pieces of junk. When firing, you could see the bullets kind of doing corkscrew out of the barrel while the kickback walked the line of fire in it’s own desired direction. It definitely could be walked onto target though...
Our mechanized unit had them in Germany in 1989. I was in a line company but I was good friends with some of the mechanics who were assigned to the M88 beasts. Along with their M-2 50 cal. and side arm M-1911 .45 they had M-3 .45 Grease Guns (All arms that served in WWII!). I was a M-249 SAW gunner and saw the simplicity of the M-3 from maintenance to use was ingenious. The belt/drum or in an emergency magazine of the relatively heavy SAW could spit 5.56 rounds at a hellacious rate but was not close to the simplicity of the M-3 take down,reassemble and maintenance. I do understand they did completely different roles.
My uncle said the same.
Were good for clearing trees of Nip snipers at Okinawa.