[SauronOfMordor]

Yeah...but since the tumbling effect was mostly observed on strikes outside of a couple of hundred yards, doesn't it make it a rather moot point on close range soft targets?

The effect I was talking about was for pre-mass-production rifles with the 1-in-14 twist barrels, from the field evaluation period.

They increased the twist for production models in the 60's in order to improve accuracy. So they got a rifle that would more accurately put holes in paper at 300 yeads -- a range there the bullet has lost so much energy that it doesn't have enough knock-down power to be effective

[Spktyr]

Actually, it was observed on the early production rifles as well; I have it on very good authority from someone who was there for several tours.

[hiredhand]

Energy transfer from 55gr .224 bullets at 500 yards is DISMAL. I was going through the charts the other day doing a comparison. We've got two ARs in the house. They're not my favorite, but I'll have to say that these have been reliable so far and we have not been "nice" to them. Also, VERYBODY can use them, from the 10 yr old, up to and including the wife!

I can't say the same for some of my .30 caliber hardware. Not everybody in the house can use it. This is mainly on account recoil and weight.

[archy]

The effect I was talking about was for pre-mass-production rifles with the 1-in-14 twist barrels, from the field evaluation period.

The original Armalite AR-15 rifles obtained for Special Forces by the Army Limited Warfare Lab [from USAF procurements, as I recall] had the 1:14 twist barrels, often helpfully augmented by the use of Remington commercial ammo, usually in the 55-grain hollowpoint loading.

The *improved* Army Ordnance Corps XM16 version used a 1:12 twist barrel, for lessened erosion with ball powder, better performance with tracer ammunition, and to meet accuracy requirements under Arctic conditions not frequently encountered in Vietnam. The resulting weapon was fairly quickly replaced by the next-generation M16A1 with a chrome-lined 1:12 barrel and a bolt assist for dealing with cases that hadn't quite chambered, either from corrosion or moisture on the brass or from chamber fouling. The features remain on today's M16A2 and M4 variants.

Most of the remaining M16 rifles we had in First Infantry Div. Circa 1968 were traded for new/er M16A1s, thence to be handed off to the Viets, Koreans or Australians. A few old much-rebuilt Vietnam-era M16s still remain in Australian ARES armouries, their new AusSteyers not being in complete issue quite yet.