Ditto, not a gun afficionado, but I've studied it a bit.
"Slug throwers" (sci-fi term for these kinetic-energy weapons) impart a packet of kinetic energy (K) to their targets:
K = mv
2
In the MKS system (meter-kilogram-second) K is measured in joules:
1 joule = 1 kg·m
2·sec
-2
To calculate and compare the K of different firearms, you need to know two properties: muzzle velocity and mass of the projectile. Here are a few examples (using MKS):
- Walther PPK ("Polizeipistole, Kriminal", police detective pistol made popular by James Bond)
Muzzle velocity -- 970 fps (295.656 mps)
Ammo (mass of projectile) -- 9x17mm (6.18 g = 0.00618 kg)
K = 0.00618 kg × (295.656 mps)2 = 540.2 joules
- Beretta M9 (adopted by US military)
Muzzle velocity -- 1155 fps (352.044 mps)
Ammo (mass of projectile) -- 9x19mm (7.49 g = 0.00749 kg)
K = 0.00749 kg × (352.044 mps)2 = 928.273 joules
- M16A1
Muzzle velocity -- 3280 fps (999.744 mps)
Ammo (mass of projectile) -- 5.56x45mm (3.65 g = 0.00365 kg)
K = 0.00365 kg × (999.744 mps)2 = 3648.13 joules
- AR 15
Muzzle velocity -- 2700 fps (822.96 mps)
Ammo (mass of projectile) -- 5.56x45mm (3.65 g = 0.00365 kg)
K = 0.00365 kg × (822.96 mps)2 = 2472 joules
Even though the AR 15's slugs are about half the mass of the sidearms' slugs, the kinetic energy they impart is about 3 times greater because of their much higher velocity; ideally, with slugs of the same mass when you triple their velocity you increase their kinetic energy by a factor of nine.
Another effect of the much higher velocity is what we saw in the video when the AR round ripped through the ballistic gelatin. I think I've heard that referred to as cavitation, but it's caused by the shock wave which would be much less for a slower projectile.
I've also heard over the years that an M16 round will tumble, especially when it enters the body, thus doing much more damage than a sidearm round would.
On the radio a few months ago the expert being interviewed described the differences in effect and had a scale for comparing the lethality/damage imparted by different firearms. The AR15 rated considerable higher on that scale than a 9mm sidearm.
As to Percy's original question/comment, I've only heard radio reports of that incident and from what I heard I would assume that a sidearm had been used instead of an AR15.
It was in an enclosed area, which would have placed him in close proximity with his intended victims. A long gun is a better choice when there's some distance between you and your target; if they are close enough to close distance to you, they would have a chance of disarming you. All they need to do to neutralize you as an immediate threat would be to wrestle the muzzle into a neutral direction. Doing that when you're armed with a sidearm would be much more difficult.
So I would think that if the gunman had done any amount of planning, he would have chosen to use a sidearm. Just my own guess.
On the subject of "slug throwers", in the armory of
Burg Eltz on the Mosel I saw something I had never known even existed. Laid out there with the other medieval weaponry was a row of
handheld catapults. They had an arm and bucket and some kind of spring to throw the arm and its payload (eg, a rock you picked up) forward when you release it, like your typical catapult. I never knew any such thing existed.
At the same castle they also had about a dozen functional miniature cannons with barrels up to a foot or two long. The guide explained that traveling armament salesmen would take those with him to demonstrate how the real thing would look and work as well as to demonstrate the quality of their craftmanship. And if you put in an order for cannons, you could keep one of the miniatures of the model you ordered. Hence the castle's collection.
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