I have a little experience with both systems:
The M60 is an open bolt weapon, the M16 a closed bolt system.
The danger of a cook off is much lower in an open bolt weapon. The cartridge soaks up a lot of heat in a closed bolt weapom after a couple a long bursts of full auto fire.
Yes, the open bolt of an M60 is an invitation for debris to get into the gun, that is why one usually
(when contact is not imminient) carries it "half loaded". (That is with the belt in the gun with the bolt closed on an empty chamber).
In my opinion, a true machinegun needs to be an open bolt weapon.
I do not like the open bolt submachineguns. The M3A1 is a an example. The bolt is a huge affair relatively speaking and when you fire it at 25 to 50 meters the forces unleashed when pulling the trigger make a good first round engagement difficult.
For accuracy the open bolt gun in a light shoulder fired weapon sucks! A true machingun is another case. First of all, if you know what you are about, you endeavor to use it from the tripod with the T&E in fixed or search and traverse fire.
Second choice should be free gun on the tripod.
Last choice to fire the weapon from the shoulder/underarm/hip in the descending order of desirability.
So to recap;
An auto rifle the closed bolt system is the way to go!
Machinegun the open bolt is the way to go.
Submachinegun, depends. For military ops I would choose an open bolt design as more reliable. For police work I would use a closed bolt system hoping for better first round/burst engagement probability.
If you are specing an agency acquisition, be very thorough and careful when you analyze your needs. If a machingun is called for, then balance out the above trade offs to gain the most for your $s ! All auto fire is fun, but not all auto fire is tactically sound nor necessary!
Ni ellegimit carborundum esse!
Yours In Marksmanship