Your Pal, the Firearm

Flechettes and Glasers and anti-tank sabot
Mossburgs and Stoners and se'en-six-two NATO
Dragon's Breath 12 Gauge and whirling shot bolos
Custom rig holsters that look like Han Solo's
Rho-desian Jungle Rounds
Worn on the sling
These are a few of my fav-o-rite things

CHORUS:

Shoot Shoot Shoot for Old Delta Green!

For honor and glory we will win!

Our ammo is endless, our barrels are clean!
and using your fists is a sin!

— "Delta Green Gunfondler's Song", Delta Green Mailing List, c.1998

Hey there, hepcats! Every now and then, AEGIS operatives need to plug the holes in American democracy like so many little Dutch boys. Only they use their fingers to pull a trigger, and they plug those holes with lead, chum! 

Now, some (maybe most) of you are sensible types and never spend a second of your day thinking about the kind of rod you'd be carrying at your hip, and that's okay! We're here to help. Slide 1, please.

Handguns

Handguns are the firearms you're going to encounter most commonly in your capacities as agents of a shadowy national conspiracy that's guided by love, mostly. Broadly, there are two types, as you know: revolvers, with a rotating cylinder containing normally either five or six bullets, or semi-automatic pistols, which draw bullets from a magazine, normally inserted into the grip. Almost all handguns of this era have a prominent spur off of the hammer in the back; federal agents and other people who wear a shoulder holster often put a pencil eraser over it, to protect their suitcoats.

Revolvers do not eject their empty shells when fired; this means you don't leave casings lying all around the ground after plugging some communist. Additionally, due to their design, if a bullet in a revolver is a dud, no action is needed to clear or prepare the weapon to fire the next round; a simple trigger pull will suffice. Conversely, revolvers cannot be silenced due to the way they're designed. (There are some exceptions to this rule, but they'd be beyond rare in 1951.) Most police forces use .38 caliber revolvers. Experienced criminals also prefer them, because they don't leave evidence in the form of expelled shells behind. Dirty Harry's original .357 Magnum is on the market, and a fun fact is that a .357 can actually fire .38 bullets as well (though the reverse is not true). 

Semi-automatics, also called commonly called automatics (even though they're not) typically carry more bullets than a revolver; usually seven in the magazine, and an additional round may be stored "in the chamber", that is, drawn into the gun and ready to fire, but this is somewhat less safe, though not uncommon. Semi-automatics eject the empty shell after the bullet is fired from the gun, then feed the next round into the weapon to be fired. In the event of a dud bullet or jam, this can require a little fiddling to clear the weapon and ready it for firing again. The USA's armed forces use the .45 caliber Colt M1911A1, and thousands of them were dumped on the surplus market after WWII. It is an exceptionally large and powerful handgun for its time. Other popular large calibers are .38, .38 Super, and 9mm. Intermediate weapons use .32, 7.65mm, or .380, and there are also plinking rounds like .22s or .25, the latter famously derided by Raymond Chandler as a bullet useful only for killing butterflies.

 

I'll update this more when I have time, if the players find it helpful.

Info from M. Thompson:

These codes are usually applied to automatic pistols, but can be applied to any firearm in describing the condition it's in. This can give you some ideas on how your character is riding with his weapon. 

Condition 1: Round in chamber, magazine loaded, safety on. M1911 has a the hammer cocked.

Condition 2: Applicable to M1911 style pistols: round in chamber, magazine loaded, safety on  and hammer is down (uncocked)

Condition 3: NO round in chamber, magazine loaded, safety on.

Condition 4: No round in chamber, magazine NOT loaded, safety on.

Generally, pistols would be in condition 1 or 2, with rifles being in condition 3. Condition 4 is used in the armory or when transporting. Revolvers may be considered to be in Condition 1 upon loading all chambers, with Condition 4 being an unloaded weapon. Our Smith and Wessons are Double-Actions. Unlike a cowboy's Single-Action Army, the initial trigger pull cocks the gun from a draw. It requires a heavier than normal trigger pull.

Your Pal, the Firearm

Red Menaces and Green Men ardentspork M_Thompson