[Nando Aqui]

In "Guns Magazine - COMBAT 2003 Annual" issue there is a very interesting and in-depth article: "Failure of the 5.56 - Are the U.S. Troops at Risk?" by Seth R. Nadel

Among other things, it explains how the original, unstable 5.56, 55-gr bullet was far more devastating to the human body than the later 62-gr, better stabilized bullet, which was more suitable to penetrate body armor.

However, there is a statement on page 48 that I question. Quote:

"... The second effect of winter is the reduced velocity of the round as it is fired. A change in temperature of 5 degrees can change your point of impact 1-inch at 100 yards, according to a sniper's log. Consider a change of 50 or 100 degrees, from the warmth of summer to the depths of winter. The change in the POI results from the lower velocity of the very cold ammo. So now we have, in a worst-case scenario, a short barreled M4 carbine, firing an over-stabilized bullet, at (relatively) low velocity, which causes minimal wounds. This may sound very hummanitarian, until your wounded opponent kills you."

I know I have shot in 95°F and 25°F weather with my AR15 HBAR, using the 55-gr round. I also know that there was no 14-inch change in POI, as the article would suggest. [(95-25)/5 = 14]

Is it possible that the author (or the sniper's log) have meant .1 (1/10th) of an inch instead of one-inch? I guess I could believe a change of 1.4" for a 70° change.

Any opinions?

Alex

[Art Eatman]

I think you're probably right about the 0.1".

The only experience I can think of was my 350-yard deer. My load testing and sighting in was done in most-likely 90-ish temperatures. I took the shot around New Year's Day, and even in Texas it was likely no more than 45 to 50 degrees.

The bullet hit within an inch of where I wanted it to hit, where I expected it to hit.

Out beyond 500-600 yards, I can see where fifty degrees of temperature can matter. But for the typical 100- to 200-yards shots, it's of no importance this side of a competition match. Heck, even 300...

Art

[Double Naught Spy]

Well, from the few times I have shot at 100 yards, ranging from about 50 degrees to 105, I feel confident in saying that my point of impact did not change by 11 inches.

It could easily have been off by 1.1 inches and I would never have noticed.

Imagine 100 degrees difference in temperature and having your shot by off by 20" at 100 yards. Heck, there are handguns that fare much better!

It must have been a mistake.

[mete]

Obviously a mistake , otherwisw I would have missed many deer since sight in is done at about 70F and hunting is done at 0-40F.

[COHIBA]

all is suspect.
i know of no sniper/scout who use a 223, much less in an AR platform to do the deed.
were my rifle to vary even .1" from 5 degrees it would be w/ the armorer.
as far as the M16 or AR platform goes, i have shot them from the hottest okinawan days to the coldest NC mornings and never seen a shift like that. in fact i remember shooting some mornings when their was frost on the ground at 0800 and we were sweating of gooseeggs off by 1300. if the change was even .1 at 5 degree shift per 100 yards then you would be looking at a 10" shift from 500 (the USMC quals KD out to 500). trust me you would notice.

[CaesarI]

Well most of the discussion in that article is suspect...
Among other things, it explains how the original, unstable 5.56, 55-gr bullet was far more devastating to the human body than the later 62-gr, better stabilized bullet, which was more suitable to penetrate body armor.
Both will penetrate "body armor" quite nicely, as long as we're talking to soft sort, and neither will penetrate the hard sort. The author also seems to be under the impression (as many were during the Vietnam war) that the 55gr round was effective because it was not stabilized in flight. This was once thought to explain the reason for the rounds performance. Later tests revealed this to not be the case. The 55gr rd is stabilized in a 1-12" barrel and the 62gr rd is stabilized in a 1-7" barrel. Both rounds will fragment dramatically in flesh, with the 62gr rd actually losing a greater percentage of its mass to fragmentation.

The greater effect on the rounds in Afghanistan is the short barrels, and long ranges. Aside from the "cool" factor, regular troops have no need for an M4.

-Morgan

[Delmar]

with todays gun powders formulated to be less temperature sensitive, I would guess the difference in POI would be more due to air density than anything else, and really doubt the article's assertion of POI shift. The 62 grain bullet is designed to better penetrate armor better than the old M198, which it seems to do, but its no long range sniper round by "a long shot", not necessarily because of its drop, but more because of its drift.

[PUMC_TomG]

I would assume this to be a load of balogna to a point. I sighted in my Scoped Rifle in about 80 degree weather... I shot yesterday in 30 degree weather... still hitting my zero....

So I doubt he's too correct. Maybe .1 inch or something... but I don't see a huge difference... unless I have the coolest rifle on the planet.

[cracked butt]

I don't think the average grunt is going to worry much about some 'tacktickle' crap published by a magazine when the bullets start flying. The soldier will put more faith in the millions of manhours of research and development needed to develop his rifle and ammunition combination than of what some hack put together in 5 minutes time to fill print space.

[Marshall]

I can tell you I have shot in the 100 degree heat of summer and 15 degree cold of winter and never touched an adjustment on my scope while still hitting precisely what I was aiming at. Although, I must admit, I didn't get out any tapes measures. :neener:

[BigG]

I think the short bbls are a mistake, especially w/ the 62g. You take a marginal ctg (with 20" bbl) and reduce it to a glorified submachinegun ctg.

[hksw]

Are you guys also taking into consideration the temperature of the ammo? It appears from the quote of the author that the subject is the actual temperature of the ammo and not just the environment. I can see where there would be very little to no change when you shoot ammo that has been sitting in room temp/humidity and going out at 110°F and doing the same at 30°F.

I can also see a possibly big difference in POI between ammo that have been sitting and equilibriated at 110°F and at 30°F. That difference in temperature would surely affect chemical reaction time and flame propagation which, IMO, would have an effect on velocity. I've never tried it myself, however, but you know what? I do have some .223 that's been in the trunk of my car for a while and some in my appartment. I think I'll see for myself this weekend.