We teach some of this stuff about shotgun gauges and calibers (not the heavy ordnance part) in the curricula for our Hunter Safety class.

 

This is anecdotal evidence, but the longer I work with the younger shooters, the more I discover all the stuff they just don't know. 

 

One of our major concerns is putting the right ammo in the right firearm.  We also caution our HS trainees about the classic 20 gauge/12 gauge blow-up -- drop in a 20 gauge and then follow it with a 12 gauge and fire.  The barrel blows up just about where your forearm, wrist and hand are.  Another is why you need to load softnose lead or bluntnose hollow points in tube feed rifles and not pointed (or "spitzer") bullets.  The recoil acts on the rounds and drives the leading round's primer into a pointed bullet where it acts as a firing pin.  The result is a magazine explosion and you go to the emergency room.  We caution them about barrel obstructions -- like shooting a sabot slug in a shotgun barrel with a choke tube installed or getting mud/snow in the barrel or have something like stuck in the barrel -- and how the barrel can blowup or the gun.  Either condition can seriously hurt or kill you.

 

Most shooters depend on the caliber or gauge being stamped on the barrel of the firearm to tell them what kind of ammo to use.  Modern firearms do, but older ones don't and neither do ex-military firearms.

 

Example: ex-military .45 pistols come in both black powder and smokeless powder loadings: .45 S&W Schofield (for their top break M1875 revolvers); .45 Long Colt for the M1873 Colt Single Action Army; .45 ACP for the M1911 series self-loaders and M1917 series revolvers.  There are major non-interchangeability issues here.

 

Example: ex-military .30 rifles come in .30-40 Government for M1892-M1898 Krag-Jorgensen rifles (a rimmed case); .30-06 Springfield or cal. .30 M1 or M2 for M1903, M1917, and M1 rifles; .30 Carbine for M1, M1A1, M2, and M3 carbines; 7,62x51 NATO (.308 Winchester) for M14 rifles.  There are major non-interchangeability issues here.

 

The bottom line is this: what you don't know CAN hurt or kill you.  I'm glad to add to the knowledge pool.