Maybe that's a problem in an M16's magazine, made to fit that straight-wall magazine housing of Stoner's AR15, and so cursed now with 30-round magazines that have to transition from a straight magazine to a curved one, the cause of much of the M16A1 and later versions reliability problems.
But the Kalishnikov and Stoner 63-derived magazine of the Galil doesn't suffer that disadvantage, and a Galil is no doubt sturdy enough to handle a 6.8 caliber upgrade....perhaps the way to go is not with a new M4 upper at all....
Not at all, though they didn't exactly *tumble*. When the bullet nose [ogive] hit a dense material such as flesh or bone, the still-spinning bullet's heavier rear portion continued its turning, often in ever-widening diameters, leaving a wound whose path resembled a funnel. That was a characteristic of the very early 1:14 twist barrels, changed to a 1:12 twist in the M16A1, particularly when the 55-grain M193 ball ammunition was used, which also had a nasty habit of breaking in half at its cannulure [bullet jacket's grooving]once it got sideways while meeting resistance. The diverging wound channels could get real nasty, and could help promote blood loss and shock, giving the old M16 and M16A2 a better reputation for stopping power, if not for mechanical reliability or long-distance accuracy, long ranges not usually being a problem in Vietnam where the usual enemy equipment were AK and SKS rifles or leftover US WWII carbines. But every now and again, someone on the other side would turn up who could really shoot.
Too, some hits were from tracers that had burned out at maximum distance, or had been fired from short-barrelled XM177E2 *Car 15s* that sometimes had the same stopping problems that 14.5-inch barrelled M4s now exhibit. If you're gonna use the 5,56mm, use it in as long a barrel as possible, and take advantage of that accuracy...if it's not a windy day.
-archy-/-
My take on the "tumbling" was that the old 55 grain ammo out of a 1-14 twist barrel (if that's what the M-16A1 was) was not too stable at best. As soon as it hit somebody it tended to fishtail and flip. The new NATO standard 62 grain ammo, fired from a faster twist 1-9 barrel, is extremely stable in flight. It was designed for NATO armies to be capable of hitting and penetrating a Russian steel helmet at about 600 yards. That's great, but when it hits Abdul at 20 feet, it often makes a clean "knitting needle" or "icepick" wound. These wounds, while ultimately fatal, don't reliably put a man out of the fight immediately. Much of their energy is wasted, as the bullet zips on through and keeps going.
The Russians have better bullet designs, which are made to flip 180* every time passing through a torso. These wounds do far more damage than a "knitting needle," ripping and shredding a wide swath of meat and organs, and going from 3,000 to almost nil fps, dumping all their energy into the shootee.
Neither have I, but I have NEVER seen a mortal man take a 7.62 into center torso - front or rear - and be able to do anything but lay down, stay down and take a dirt nap. Hits in less fatal locations, would still knock the bastard down, usually with a sudden loss of interest in further aggravating you.
Had I seen anyone take two or three shots to the chest, and then fire at me after I went by ---- I would surrender to the bastard!
The unforgivable drawbacks with the sweet M14 - is Length, Weight and Bulk of piece and ammunition, and it does not lend itself to being brought to bear in close confined places.... I'm all for a light, short piece - but I believe one would have to insist on a projectile and ballistics that will convince the target to DIE!
Our guys should have a weapons system that can KILL...not injure... For the in close building clearing operations - what the hell is wrong with a sawed off shot gun? Don't laugh when I mention the reliable killing functionality of the ancient .45 ACP firing Thompson Sub-Machine gun... It's a short piece - and the round in close is effective.
Frankly, I can't keep up with all the new weapon systems they're coming up with -- it seems every month they come up with a new platform... This can't be good...especially if they're simply "bad" looking but ineffective for the purpose they're intended --- to KILL RELIABLY. I don't think the enemy is impressed by "bad" high tech looking weapons --- but they do respect an effective weapon...
Semper Fi