Nope, and not even that dual feed systems, belt AND magazines are a bad idea- only that it doesn't seem to have worked real well with the M249. Which may well be why the USMC wants something better.
You ignore the Gatling gun and the Sten, as well as the Bofors, and any side fed gun such every single belt fed machine gun ever produced.
As well as the German FG42 and Johnson M1944 and the Israeli Dror, all of which fed from magazines from the side, and the German Knorr-Bremsen and MG13, which used box and double-drum [trommelmagazinen] In weapons that used full-power rifle magazines, they were clunky and unbalanced; I've handled all of them, shot a FG42 and owned an MG13. Clunky.
And I don't even want to think about a Gatling [.45-70!] with the Accles feed *doughnut* drum as a handheld weapon; though some .30-40 caliber Gatlings were fielded, those used by Cpt. *Gatling* Parker in Cuba were .45-70...and on wheeled mounts.
A weapon used for suppression fire needs to be able to fire more than 30 rounds before reloading.
Concur.
If not, then you need to change your tactics such that squad members will only advance if they can reach cover before the machine gun empties a 30 round magazine.
My view: having the SAW in use by a squad of riflemen makes it desirable that the weapon can be fed from the same magazines as the squaddies rifles, assuming that a more powerful cartridge or loading for the SAW isn't used; that's the trade-off. Having the weapon feed from either a belt or magazine seems okay, IF and only IF reliability isn't compromised. The tradeoff penalty here is additional weight and complexity, but it can be done.
The real answer could be reliable large capacity drum magazines such as the 75-round RPK mags or Beta-C 100-round magazines some USAF teams use. They're a bit fragile, but as a first generation prototype, could be better developed. Or we could just go with belts.
An alternative: an interchangable barrel system for the AK, allowing a cutdown short barrel to be fitted for assault vehicle crews, or a standard one for Joe Snuffy, Rifle Grunt, or the RPK barrel for the big guy in the squad who can hump the extra weight and extra ammo...or the corporal who better knows what to do with it. That way if in use a firing pin or extractor lets go, the squad is not out of business until it gets the SAW back running again, but the SAW gunner simply removes his barrel and hands it off to anyone nearby with another interchangable-barrel AK. The second guy fits the heavy barrel, and the team is back in business again; either the RPK gunner can give his ammo belt to the new SAW gunner or he can simply trade guns with #2, leaving the other guy to clear the stoppage in the receiver of what had been the SAW and get back to work. Having a few extra heavy spare barrells around could be a nice idea, too: sounds like prime trade goods for scroungers to me.
Two other deseriarta: belt-fed guns ought to be capable of being fed from either side, as per the Browning M37 .30 and the .50M2. this makes such activities as use in vehicles a lot less complicated [you do know that US AFVs mount the co-ax MG on the left interior side of the turret, while the ex-Soviet vehicles fit them on the other side, don't you?] this also allows twin-gun mounts that feed to each gun.
And the possibility of having platoon MMGs *downsized* to use the smaller primary rifle caliber is possibility, as seen in the South African SS77, both a 7,62 and 5,56mm capable gun. This could result in an over-heavy 5,56mm gun, but the Navy has beenn going in the other direction as well, turning the 5,56mm M249 into a 7,62mm gun as...but eliminating the magazine feed.
