I watched a program on the Military History Channel Tuesday (I think - it took me this long to calm down) titled "The Works — Guns and Ammo" which may have been originally broadcast on 8/14/2008. It seemed to be pitched to the 'low-information voter', so I tuned in to see what they're being told. This is what I 'learned' (among other things):
- The M-16 is a semi-automatic. Well... yes, the M-16 can fire semi-auto but it's really a 'select fire' arm: full-auto, 3-shot burst, and semi-auto. The M-16 is thus a true "assault rifle".
- The recoil of an M-16 is light because the muzzle brake reduces it to a manageable level. Ah... no. the recoil of an M-16 is light because the puny .223/5.56mm round doesn't produce much oomph. A muzzle brake keeps the recoil from taking the rifle far off its aim-point.
- The flash hider hides the shooter's position from the targeted enemy. Absolute balderdash. A flash hider hides the flash from the shooter for the purpose of retaining the shooter's night vision capability.
- The AR-15 is 'AR' because it's an 'Assault Rifle'. No, it's called an AR-15 because it was first produced by the Armalite Corporation which labels all their models "AR-something". In fact, if you ask the CSGV (Committee to Stop Gun Violence), they will call an AR-15 an "assault weapon", a made-for-TV term that means "scary-looking guns we would like to ban forever".
- If you fire a bullet absolutely straight up such that it would fall back onto your head, it will expend all its energy getting to altitude and when it finally gets back down will bounce harmlessly off your head. (Do NOT try this at home.)
That last really ices the proverbial cake. It calls into question everything I've ever seen on the Military History Channel; everything.
Let's talk physics. I fire a bullet absolutely straight up (ASU) at 1,180 fps (feet per second). The acceleration due to gravity is 32 ft/s/s, so the bullet will rise for (1180/32) 36.875 seconds and it will attain a height of 21,765.25 feet (4.12 miles). At that instant, its upward velocity will be zero. It will then begin to fall — 21,765.25 feet. It will fall for 36.875 seconds (sound familiar?). When it finally strikes your head, it will be traveling 1,180 fps. Yes, it expended all its energy getting to a height of 4.12 miles. Then it gained it all back by falling that same 4.12 miles.
"Bounce harmlessly off your head"? Uh... probably not. There is one odd thing that happens, though. As the bullet exits the muzzle, it will be spinning because of the rifling inside the barrel, and it could be spinning 2,000 rpm. Although the bullet loses its vertical velocity, it loses very little of its rotational velocity. At the top of its path, vertical speed zero, it is still spinning at about 2,000 rpm, and it will continue to spin, nose up due to gyroscopic forces, as it falls those 21,765.25 feet.
So, a word to the wise: whatever you see on the Military History Channel should be taken with a very large ration of salt, especially when they tell you that the Fokker D-7 was "reluctant to spin". A plane reluctant to spin is also reluctant to turn, and this is not a good thing in a fighter airplane.