Stupid question about guns

[Husar]

Ok, so if the two rounds reach their target with the same kinetic energy and have the same shape and materials (+ density), the 5.56 is faster and the 7.62 has more mass, but overall kinetic energy is the same as I said, would there be a difference in penetrating power? Would the mass of the 7.62 help it penetrate because it simply is harder to stop and would the smaller size of the 5.56 help it get through as it has to "cut a smaller hole" to get through whatever is in it's way?

I'm wondering about this because if caliber and weight are so important, why do tank gun designers increase the velocity of their penetrators instead of weight and caliber? I would think a very, very fast small bullet should cut through armour quite well, after all it take less energy to shove a needle into your skin than it takes to get a pencil there., even if it's a very sharpened pencil, or am I wrong? (not feeling like testing that last thought right now )

[rvg]

I'm wondering about this because if caliber and weight are so important, why do tank gun designers increase the velocity of their penetrators instead of weight and caliber? I would think a very, very fast small bullet should cut through armour quite well, after all it take less energy to shove a needle into your skin than it takes to get a pencil there., even if it's a very sharpened pencil, or am I wrong? (not feeling like testing that last thought right now )

5.56 being lighter runs out of loses velocity faster than 7.62 which means that the longer the distance of the shot, the better 7.62 is compared to 5.56

at 50 ft either caliber is pretty much guaranteed to kill regardless of body armor

at 300 ft 5.56 is significantly weaker than 7.62

[Vuk]

Ok, so if the two rounds reach their target with the same kinetic energy and have the same shape and materials (+ density), the 5.56 is faster and the 7.62 has more mass, but overall kinetic energy is the same as I said, would there be a difference in penetrating power? Would the mass of the 7.62 help it penetrate because it simply is harder to stop and would the smaller size of the 5.56 help it get through as it has to "cut a smaller hole" to get through whatever is in it's way?

I'm wondering about this because if caliber and weight are so important, why do tank gun designers increase the velocity of their penetrators instead of weight and caliber? I would think a very, very fast small bullet should cut through armour quite well, after all it take less energy to shove a needle into your skin than it takes to get a pencil there., even if it's a very sharpened pencil, or am I wrong? (not feeling like testing that last thought right now )

At that point I think the 7.62 would still have the advantage as it would retain its mass better than the smaller 5.56 which would break up a lot faster.

[rvg]

perhaps not entirely on topic, but this is my all time favorite article about large caliber penetration...

http://www.mit.edu/people/daveg/Humor/ravioli_as_gas

[Husar]

2.) Mass helps armor peircing. An Abrams Anti-Tank Round (called a Sabot) has a Depleted Uranium tip, among who's unusual properties include a tendancy to get sharper the further it burrows into armor. Other nations prefer Tungsten. For Armor-Peircing bullets, I believe Steel and Lead is still the standard for making them heavier--although all kinds of specialty bullets exist for bigger-calibre guns. IIRC there is a Sabot-style .50 Round, but I'm not sure if it has DU in it.

Yes, the question is, what makes for betterer penetration, more mass or more speed? For example sabot, you have a 120mm cannon, the actual tungsten rod that hits the enemy in the end is maybe 50mm or less in diameter, the point being that when fired from a smoothbore gun it can have a much higher speed and thus more penetration.

If mass were the bigger factor in penetration I would expect them to use a 120mm rifled gun and fire a tungsten rod that is 120mm in diameter and thus has a whole lot more mass but is also slower. Of course the latter would retain more efficiency at longer ranges but the decision went towards the former because at the usual ranges tanks engage eachother, the smaller projectile with higher speed has a better chance to penetrate the target.

It's also notable that german guns with lower calibers in WW2 often had better penetration characteristics than larger caliber guns of other nations because the projectiles had a much higher velocity AFAIK.

Why would the penetration of an assault rifle bullet be much different?

At that point I think the 7.62 would still have the advantage as it would retain its mass better than the smaller 5.56 which would break up a lot faster.

Why would the bullet break up faster if it's the same material, same density and same form? The kinetic energy is the same after all, which also means that the smaller bullet concentrates the same kinetic energy in a smaller area, which usually makes a difference in penetrating power.

Due to the higher speed of the smaller bullet the material being hit also has less "time to react" as was also somewhat jokingly mentioned in rvg's link.
The smaller bullet would simply concentrate the same kinetic energy in a smaller area, helping it to punch through in that smaller area.
I know mass also plays a role in which object gives way in a collision etc., the question is which effect s bigger?

[Vladimir]

You're German. Find the formula to calculate kinetic energy and it will answer your question.

[Husar]

You're German. Find the formula to calculate kinetic energy and it will answer your question.

I know it, I was asking about the same kinetic energy but with different mass and diameter, basically whether kinetic energy is the only factor or not.

Vuk and rvg seem to be saying that a bullet with higher mass and bigger diameter is superior to a smaller but faster bullet even when the kinetic energy is the same.

[Vuk]

I know it, I was asking about the same kinetic energy but with different mass and diameter, basically whether kinetic energy is the only factor or not.

Vuk and rvg seem to be saying that a bullet with higher mass and bigger diameter is superior to a smaller but faster bullet even when the kinetic energy is the same.

That is not what Vuk is saying. Sectional Density is the ratio of an object's mass to its cross-sectional area (Wiki link). It is what makes a needle penetrate skin better than a copy of the unabridged War and Peace. Heavier rounds tend to have a better sectional density. A 7.62 usually has superior SD to a 5.56. SD and velocity are the two most important factors in determining whether or not something will penetrate armour. Basically mass is important, but it needs to be concentrated into as small an area as possible.

[Husar]

That is not what Vuk is saying. Sectional Density is the ratio of an object's mass to its cross-sectional area (Wiki link). It is what makes a needle penetrate skin better than a copy of the unabridged War and Peace. Heavier rounds tend to have a better sectional density. A 7.62 usually has superior SD to a 5.56. SD and velocity are the two most important factors in determining whether or not something will penetrate armour. Basically mass is important, but it needs to be concentrated into as small an area as possible.

I see, it confused me because I kept on saying that factors like density would be the same, yet you kept saying the bigger round is better.

Good to know we can agree on that though, I wouldn't even have a copy of war and peace handy to prove you wrong.