Muzzle velocity in winter

[Sergei]

One of the big differences between west and east front was the winter climate. In east things can get lower than -30 degrees Celsius, or below -20 in Fahrenheits, and at those temperatures it also started to effect matters.

Now, I was thinking about how in army we were told that if we don't warm up our 95mm AT grenades before battle, then their muzzle velocity will be lower (as the initial temperature is lower when the explosive ignites and it won't produce as much energy as rapidly).

So we were instructed to not expect ourselves to hit the target as easily in winter, because the velocity wasn't constant. We operated an RPG launcher which fired HEAT rounds, so it didn't have any difference on actual penetration (or maybe it does if a cold HEAT reacted more slowly as well?). It would be interesting to know, therefore, did very cold weather have any important effect on kinetic energy rounds. Does someone know any exact information?

[edgars]

I'm thinking that in a tank most of the shells lies pretty close to the engine which may heat things up a little. This of course is not the case with AT guns...

[Dan Robertson]

I have seen statistics on Russian test of steel APFSDS where penetration went down up to 20% when the rod was cooled to -20 degrees.

I suspect this would happen to AP rounds too, though they are heated more by friction since a DS round has a sabot.

[voidhawk]

<blockquote>quote:</font><hr> I have seen statistics on Russian test of steel APFSDS where penetration went down up to 20% when the rod was cooled to -20 degrees. <hr></blockquote>

Wonder if they cooled the target down to the same temperature too? Steel gets more brittle with lower temperatures, so you'd expect that to apply to the target too.

Another effect to consider is the shrinking of a gun barrel's internal diameter as it gets colder, thus "squeezing" the shot more, and thus increasing its muzzle velocity. I'd imagine the gun barrel would heat up pretty quickly after a couple (few?) shots though.

[Sig]

<blockquote>quote:</font><hr>Originally posted by Dan Robertson:

I have seen statistics on Russian test of steel APFSDS where penetration went down up to 20% when the rod was cooled to -20 degrees.

I suspect this would happen to AP rounds too, though they are heated more by friction since a DS round has a sabot.<hr></blockquote>

Interesting. Just curious to know: if the projectile is so heavily affected by temperature, what about the armour? Does the temperature gradient (interior heated to +?? celsius and exterior at, say, -30 celsius) affect resistance? Is armour rendered more brittle? Does this compensate for decreased resistance of the penetrator rod? Oh, and also (more related to modern armour): what is the effect of said temperature gradient when the armour is layered, and made of different materials (steel, ceramics, etc) with different dilatation coefficent? Does this cause structural damages, or micro-cracks, or..what?

Looks like we need some specialist in metal engineering or the like. High-tech grog wanted.

Like JasonC sometimes says: "inquiring minds want to know"

Sig

[voidhawk]

Getting a little off-topic, some interesting links below for some examples of effects of cold temperatures on steel:

http://www.disastercity.com/titanic/index.shtml

http://www.cts.umn.edu/T2/TechExch/2001/julsept/hoan.html

[Michael Emrys]

<blockquote>quote:</font><hr>Originally posted by voidhawk:

Another effect to consider is the shrinking of a gun barrel's internal diameter as it gets colder, thus "squeezing" the shot more, and thus increasing its muzzle velocity.<hr></blockquote>

How do you figure that? I would expect a shrunken barrel to lower MV for two reasons: Increased friction on the round as it passes through the barrel and, less importantly, slightly reduced base area of the round for the propelling gasses to operate on. Admittedly, this last is probably negligible. But for the sake of argument...

Michael

[voidhawk]

Reduced gas leakage.

I seem to remember there were guns with a tapered bore (tapering to a smaller diameter) that, in conjunction with a "softer" projectile base, would increase the muzzle velocity. Can't quite remember what they were called, but "squeeze gun" comes to mind. I'd expect it to play havoc with barrel life though.

Ah hah - found a link - for instance, see the following for the "Littlejohn" 40mm gun taper bore adapter:

http://www.users.globalnet.co.uk/~autogun/sgun.htm

[voidhawk]

Then again, the Littlejohn adapter actually has holes in the barrel to allow the gas to escape...it used a special projectile too.

So, perhaps not relevant at all. Now back to your scheduled programing...

[Terence]

Paging Rexford to the Muzzle Velocity in Winter topic. Paging Rexford to the topic. Paging Rexford.

[Michael Emrys]

<blockquote>quote:</font><hr>Originally posted by voidhawk:

Reduced gas leakage.<hr></blockquote>

I'll leave that one to the experts, but I have my doubts.

<blockquote>quote:</font><hr>I seem to remember there were guns with a tapered bore (tapering to a smaller diameter) that, in conjunction with a "softer" projectile base, would increase the muzzle velocity.<hr></blockquote>

True, but the idea was sort of like that of the APDS. You start out with a round with a basically oversized base. That gives it an increased base area for the propellant gasses to act upon. That's when the increased acceleration occurs. Then the tapered barrel slims the projectile down so that it has reduced aerodynamic resistance after it leaves the muzzle. That makes up for the friction losses it suffered passing up the barrel. It retains more of its velocity on the way to the target. I believe the tungsten the core of the round was made of had a higher density too, which would have also have helped it retain velocity.

Michael

[argie]

And the aerodinamics?

The air pressure must be higher with low temperatures, thus making the shell decelerating faster.

[voidhawk]

Michael - I agree with your analysis about the purpose of a tapered bore; mine does seem a little shaky...

Hey, but what about the cold fingers of the gunner?

[Michael Emrys]

<blockquote>quote:</font><hr>Originally posted by voidhawk:

Hey, but what about the cold fingers of the gunner? <hr></blockquote>

Yeah, okay. I'll buy that!

Michael

[L4Pilot]

<blockquote>quote:</font><hr>Originally posted by argie:

And the aerodinamics?

The air pressure must be higher with low temperatures, thus making the shell decelerating faster.<hr></blockquote>

The air pressure isn't necessarily higher in cold weather, but the air density almost certainly is. This would cause projectiles to deaccelerate more quickly after being fired and alter the trajectory. I don't know if WWII AFV's took this into account, but I'm pretty sure modern MBT's have an "air data computer" to compensate for variations of air density.

[argie]

<blockquote>quote:</font><hr>Originally posted by L4Pilot:

The air pressure isn't necessarily higher in cold weather, but the air density almost certainly is. This would cause projectiles to deaccelerate more quickly after being fired and alter the trajectory. I don't know if WWII AFV's took this into account, but I'm pretty sure modern MBT's have an "air data computer" to compensate for variations of air density.<hr></blockquote>

That's was I was trying to mean

Thanks.

(I was trying to show my new sig also )

[ 11-09-2001: Message edited by: argie ]</p>