I spent a few years as a drill sergeant and was assigned to the ranges. So I trained in the M2HB, M-60, M-203 and of course the M16A1. I left the military before the M-4 and don't know much about it. We didn't have the burst setting yet. We were still using the LAW, which I think has been out of the system for some time. The SAW was brand new.
We had a hard time training M-60 shooters to fire off six round bursts. They'd either shoot to few or too many. Firing six shot bursts and then counting to five between bursts you could pretty much keep the gun firing as long as you had belts of ammo to feed it. Sustained fire was something like 200-250 rounds per minute. Even at that rate the gun got HOT and at night it'd glow red. During the day the barrel would smoke. They gave us asbestos gloves so that we could grab the hot barrel and change it out with another.
Our 50's were fired with your thumbs. That gun had a head space issue. Each gun had its own gauge. They fired pretty slowly, but with gusto. Bam, bam, bam..... It was pretty easy to pickle off one round. But man! What a wicked round & gun! We used to say the M-60 said, "gonnagetchagonnagetchagonnagetcha". The 50 said, GOTCHA....GOTCHA....GOTCHA.
I'll tell you what. If some of you young guys want to shoot some darned amazing weapons then do a hitch in the infantry; marines or army. I was in both services. I even spent time as a pilot; yeah a weird career. I liked each for different reasons. If you have the guts and want to fight and live in the dirt, then join the Marines. If you want a career I'd suggest the Army. Either way, you will eventually lose your hearing.
One more thing. I'd not suggest that anyone join the military during peace time. You need a war. Promotions are better, there's more stuff to work with and it's more fun. Peace time is inspection after inspection and meaningless run after meaningless run and they make things up to make you miserable. It is all make-believe; you need the real thing to do any good.
No one works harder than an infantrymen. No sleep, the food is well...iffy. You stink like hell and the thought of an 8 hour day is ridiculous. You'll work three 24's, snatch a little shuteye (you'll be able to sleep standing up) and then go for another three days straight. Days flow into oneanother. You work in a fog of fatigue. If you get into a fight you'll run on adrenaline. You'll chew on the dried coffee in your MRE's.
It feels funny when you finally get home. You will also be amazed how civilians can complain about how hard they work. Some of us missed the excitement. I know I did. Lots of grunts became cops, soldiers make good cops. I became a high school teacher, but I stayed in the reserves because I felt so at home there. Now I'm too old to play soldier anymore. I've been out for decades. I missed the desert, but trained people for it. I'm enraged at the ROE that the troops have to work under. I blame liberalism, but I blame liberalism for pretty much all bad things.