Part of my AD&D House Rules, Part 1

AD&D is a system that grows with you. It has rules for most edge cases that you'll encounter and all of  the common ones. It's the game you won't get right, but by virtue of practice you will be allowed to bring yourself back in line with the game. Being in line with the game isn't following every single rule to the letter, it means keeping the rules ecosystem intact. There's nuanced layers to what the game has written that give you the long term game outcome that other systems fail to provide, there's generally always a way to handle most situations even if you don't remember it all, and there is an ecosystem that says from beginning to end: we want you to see the entire game.

With that said, there are a few deviant and divergent rules that AD&D DM's have from table to table. It was always like this and every experienced DM has their reasons. I think those reasons are generally very interesting because it illustrates what that DM is looking to manifest at the table.

There's some big collections of house rules out there to consider. I'd suggest starting with Trent Fosters The Heroic Legendarium. Kellri's blog has some useful tools for house ruling and RAW alike. EOTB's OSRICrpg.net has a collection from many areas of the net that serves as a great jumping point to head down the rabbit hole.

 

For my game, I'll start with a few rules on missile weapons.

• Crossbows that are already loaded always fire off first at the beginning of a proper combat round, barring spending segments on movement. 
• Thieves can use short bows.
• Clerics can use slings.
• Since I am operating off of OSRIC, there are interpretations that I choose to ignore such as surprise granting ranged weapons TRIPLE the rate (second example of DMG page 62). One could extrapolate that a bows rate is 2/1, a surprise segment could allow a round of actions, therefore two surprise segments (12 seconds) could see 6 fired bow shots.
  

The crossbow is nerfed enough.

 

Crossbows

Crossbows in AD&D are generally not as advantageous as a bow of any kind. OSRIC takes a step in addressing this by increasing the damage.

You can google the subject and find countless conversations on it. Where I landed is that first I thought about what I wanted crossbows to be in my game. You always see them like a gun, in that they are loaded, a trigger needs to be pulled, and that's it. It's supposed to be a threat and that threat is that this crossbow bolt is going to fly at you faster than you'll draw a bow, close into melee, or even throw a dagger.

So, I kept both the OSRIC increased damage and the ability to have a pre-loaded crossbow fire first. In terms of fulfilling the role of a gun, once characters stop having 3 hit points, it becomes a lot less threatening. But as a game consideration, it's quite valuable. 

In a surprise situation, a pre-cocked crossbow is going to get it's shot in anyway for a 1 segment surprise. For a 2 segment surprise, they are actually able to re-load and fire. The effect isn't really seen there, other than moderately better per-hit damage, but still at half the rate of a bow. 

However, most combat doesn't start with surprise segments. The first melee round will start and this is where a pre-loaded crossbow shines. You can take aim at the casting magic-user, you can shoot the orc charging you as it crosses it's double-speed distance.

Bows fire at double the rate, which still makes them the generally more attractive option. However, I did do what I set out to do: If someone uses a crossbow in my game, it doesn't feel like it's completely worse than the other options.

Thieves with Shortbows

I admit that two nonsense reason went into this house rule. Firstly, I got used to how UA and AD&D2e handled thieves with shortbows. There, I admitted it. Secondly, probably less nonsensical, is that I always equate a lot of bandits, robin hood, and the like as thieves in the AD&D world. You may disagree, but I always see them using a shortbow as thematic. 

The mechanical reason is that thieves don't usually get a whole lot to do in a fight. There's not always room for backstab and if there is, all these rolls need to be made to get there, and then you have to ask yourself if it's worth it. A level 4 party encountering 5 orcs? Just wait and let the fighters and cleric chew through them up front or the magic-user to skip the encounter with sleep or turn it into an opportunity with charm person.

Next, bows just aren't that hard to use at shorter ranges. Sure, a longbow man will have to arc their shots more and that takes skill and practice. A short bow while shooting down a 40' hallway is not something I'd limit to Fighter/Ranger/Paladins.

Clerics with Slings

Clerics can use hurled rocks. I don't care. They hardly ever will anyway, but it's nice for them to have that option. Clerics are not paladins, they don't have the same sort of honor code about missile weapons being cowardly. Go ahead, let them use a 1d4+1 sling that fires once per round.

Ignoring the 3x Surprise Interpretation

I shouldn't have to justify why having a 2-in-6 chance to get 1 or more surprise segments at THREE times the rate of fire is ridiculous. It would function just like critical hits and fumbles; Sure, it sounds cool that your players are going to be able to pin-cushion 24 arrows before the first proper round starts. But how good is it for your campaign if your characters of 6 months get 24 arrows shot into them with no counter play? It's too swingy

Overall, missile weapons are balanced in AD&D in that they are extremely good while range and the complexities of melee aren't a factor. They become near useless when your fighter, paladin, and cleric are wading through a melee with five possible targets and even if there's targets behind them, shooting over your party is often a mistake as well. It's okay to tweak them a little, it won't hurt your AD&D game as long as cover rules and firing into melee are there to keep it in check.