ARs didn't really need to have 1-7" Twist and how it was determined that they would.

[lysander]

Just one thing about the 1-7 twist....

The length of the FN designed SS110 tracer was 1.10", weighed 64 grains, and had a muzzle velocity of around 3100 fps. The M856 Tracer is identical. Running that length, velocity and weight through a number of stability calculators, a twist rate of 1-in-8 WILL NOT stabilize that projectile at tempratures of 32 degrees F or lower.

In order to keep the tracer bullet stable at below freezing temperatures, you have to go with a 1-in-7 twist. So the twist rate HAD TO BE 1-in-7.

Unless you thought the Army was not planning to go to war if the weather got chilly.

EDIT: Oh, and BTW, the IVI designed XM288 tracer, also needed a 1-in-7 twist if the temperature was going to be under -65 F, it would be marginally stable at -40F with a 1-in-8 twist.

So, really, you either kept the short M193/M196 bullets and the 1-in-12 twist, or you switched to 1-in-7.

Oh, and another BTW, tracer is issued to infantry for use in rifles like the M16, how do you think that fighting at night is done? Especially in the 1980s before wide spread NVG issue.

The Major (actually, he was a CWO 4 at the time) was the correct decision.

[Humpy70]

I wasn't aware M856 tracer was being issued to troops in 10 rd stripper clips and I have never seen it since? I have only seen it in belts. Guess something has changed. That is why the Engineer in Charge Brunton told us the A2 did not need a faster twist.

[mlberry]

McNamara and his "whiz" kids did untold damage.

[lysander]

M196 was packaged in 10 round stripper clips, I have no idea why he would have thought that the new stuff wouldn't need to be. And, seeing the Army had absolutely nothing in the inventory before the M249 that shot 5.56mm, except the M16A1, and they bothered to spend $138 million, and 10 years getting the M196 to work acceptably in the M16A1, makes his belief that the new M16 wouldn't need to be compatible with Tracer even more questionable. (EDIT; Not to mention the 100s of millions of rounds of M196 consumed during the Vietnam War)

Maybe that's why we called the Picatinny Arsenal "Pick-a-ninny", they had no idea our operational requirements . . . .

And, just because clipped M856 isn't common, as such, does not mean it is not issued to troops in fiber boxes. We shot a lot of that stuff in M16s during my time. We loaded 1 in 5, one tracer, half a stripper clip, tracer, the rest of the stripper clip, repeat.

[lysander]

PEO Ammunition Systems Portfolio Book

Page 174:
M856, A063 [for use with] M16A2
M856A1, AB74 [for use with] M16A2

TM 43-0001-27 - Army Ammunition Data for Small Caliber Ammunition

Page 10-21:


You can go back and look up field manuals (FM 7-10 for one) all the way back to 1941, that detail all the uses of tracer ammunition by infantry riflemen, besides 1-in-4 for machine guns.

"... told us the A2 did not need [tracer]...", the man that said that is just stupid. He may have been a weapons engineer, but he certainly didn't have a clue how those weapons were employed. Thankfully, Wincentsen was around.

[1_click_off]

This should be sticky status so it doesn’t get buried.....

[alx01]

You would not believe the badmouthing McNamarra got. He was absolutely hated by everyone in the office I worked in and if he had died when I was there I am sure there would have been a party you would remember forever. Words cannot describe how they loathed him.

I'm not really into AR history, but out of curiosity who's McNamara and what did he do to piss you guys off so badly?

[JediGuy]

Robert McNamara.

I suggest google and any number of articles and books written by people (such as my dad) who would be happy to know he is in eternal torment. OK, my dad is a pastor so not that extreme, but the person he dislikes more than Communists and less than Jimmy Carter would be Robert McNamara.

[Diamondback]

Robert McNamara.

I suggest google and any number of articles and books written by people (such as my dad) who would be happy to know he is in eternal torment. OK, my dad is a pastor so not that extreme, but the person he dislikes more than Communists and less than Jimmy Carter would be Robert McNamara.

AKA "Mr. Strange," Piss Be Upon Him. Very few of those I've encountered who served while he was SecDef had anything at all polite to say about him and his band of "Whiz Kids." He's one of the big reasons why the technology breakthroughs of the SR-71 Blackbird weren't exploited and built upon, just for one, along with the insistence that "we don't need bombers anymore the ICBM's will do everything needed."

But I'm just another "damn disgusting 4-F basement dweller" who's been picking the brains of notable figures in aerospace history at Museum of Flight events in Seattle since I was a small child, what the hell do I know?

[Alpha-17]

RE: Tracer use by Riflemen

I'm a little too young to comment on the use of tracers during the 80s, even if technically I was alive by that point, but I will say that I think the decision to use the 1:7 twist was a fortuitous one. Tracers are super useful to have, and I used them when they were available on deployments. Heck, I still use 'em for my rainy day ammo stash. Everyone has their own loading technique, from 1:4, 1:5, bottom three, whatever, but that just shows how widespread the practice is.

And that's not even going into the options 1:7 opened up for longer, heavier bullet types used today.