25, depending on the follower.
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.
The GI M16 and M16A1, as *improved* by Army ordnance, had 1:12 twist barrels, changed from the earliest Armalite AR15 rifles distributed in-country by the Limited Warfare Laboratory and the USAF that had 1:14 twist tubes. The reason supposedly was ordnance fears about bullet penetration and stability under arctic conditions, not something I immediately recall experiencing from the few years I was around Southeast Asia.
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.
Indeed, the M16A2 rifle, suitably reworked into a National Match version, makes a pretty fair 600-yard National Match course rifle, as recently used successfully by several competition shooters. I've been sufficiently impressed to consider a match M16A2 service rifle upper for my old AR15 clone, whose trigger I'm very happy with and used to.
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.
More to the point, the Russian ammo is designed from the start to be used from the barrel of a 16-inch barrelled 5,45mm weapon, the AK74. And it works just fine in one, though the results in the shorty AKSU tanker's version have been reported as much less satisfactory. In my own experience, I've got an EX-USAF lady friend who far prefers her 5,45mm SAR-2 to the various M16 family < rifles she qualified with and practiced base defense activities with during her USAF service. And the more I get to try it, the more similarly impressed I become, and the more I look forward to a lengthy exposure to the use of a 24-inch barrelled RPK74.
FYI, Remington is now listing the 6.8 Remington SPC ammo in its on-line catalog, and says this about it:
Developed in conjunction with the U.S. Military, the 6.8mm Remington SPC provides greater downrange effectiveness and ballistics than the 5.56x45mm. It’s unique design is based on the 30 Remington case, which has been necked down to 6.8mm(.277).
It's available in Match and Express Core-Lokt (BTHP and metal case)
Midway USA is listing three 6.8mm Remington SPC cartridges, at these prices for a box of 20:
$14.45 Remington Express Ammo 6.8mm Remington SPC 115 Grain Boat Tail Hollow Point
$12.90 Remington Express Ammo 6.8mm Remington SPC 115 Grain Metal Case
$17.45 Remington Premier Match Ammo 6.8mm Remington SPC 115 Grain MatchKing Boat Tail Hollow Point
The status is listed as "coming soon."
I think if I go and jump on the 6,8mm bandwagon, it'll likely be in a Robinson Arms *Expeditionary Rifle* with interchangable barrels, likely a fairly short one in the *bren gun* configuration. With something else for a bipod.
