Friday, October 22, 2010

Gun penetration

I can't recall playing a roleplaying game where there was weapon penetration modelled. I mean, that when you shoot someone, bullet goes through him and does damage for an object or person behind him.

I am currently thinking about rule for ammo penetration for my roleplaying system YDIN. I have an idea technically how to do it, and without testing it yet, I think it will work fine. Actually, on paper (computer screen) and in my mind it sounds really good!

One thing I am wondering is, what weapons are capable to penetrate object. Is it about speed of bullet or about caliber? This I have to find out. I cannot imagine that .22 pistol can penetrate anything that well, but .50 handgun (cannon amirite?) would more easily. Or a robust rifle.

I have to find out what are the terms gun might penetrate an object or person. After I figure it out, I can write it down as rules.

Also, I have basic rules, character creation and advancement, skills etc. written down but haven't wrote yet combat rules. When I get this penetration thing done, I can start to write combat rules here also.

And that firearms penetration system... it will be the same with melee weapons. With same system you can penetrate your opponent with sword, axe or spear.

One thing in my mind developing my own system is, that you have these basics what are used for whole system. So you can easily write rules, and they will work as anything else. I don't like games, where skill checks, combat checks etc. are handled with different rules. Ofcourse there are some differences in rules in different situations, but I want the core of how things work to be similar with each other. And I want it to be that way, that if you want to mod the game, you can do it quite easily without heavily tearing apart whole system.


Shimoroka said...

Hi, first time reader, first time commenter,

I've been working on my own RPG system on and off for a few years and bullet penetration was one things I was also looking into a few years back. A lot of the sources I explored including real firearm statistics are dead (Damn you Geocities) and my notes are a little scattered but how I devised it was like this:

Situation #1: Let's say I got a pistol, like a Beretta, and roll 22 damage (arbitrary system). The victim (constitution 15) of that bullet is wearing a light kevlar (protection 15). The bullet strikes him and the vest absorbs 15 points of damage, the round still has leftover damage thus it penetrates the vest and into the meat dealing 7 damage. No exit wound but feeling the pain.

Situation #2: I use a rifle and one round is dealing 35 damage. Same dude, same protection. Bullet hits vest (35-15), 20 leftover hitting meat (15-20), 5 leftover exiting the back hitting the vest again (15-5). Now the bullet made an exit wound to the target but not through the back of the vest.

I must say I haven't looked into what your system is yet but nor but in DnD it could be translated with an arrow. If said piercing projectile deals more damage than the victim's AC, it penetrates through and whatever leftover damage can be dealt to the unlucky one who was standing behind.

Unsure if my reasoning is okay. Though I am very curious as to other comenters ideas. My firearm system I am retooling for my RPG will also include damage reduction based on distance from target.


— Chauncey

Granger44 said...

I've seen several systems with rules for shooting through cover; those rules could probably be adapted for penetration and the possibility of an exit wound and damage to another target behind the first target.

GURPS has a rule for it called overpenetration. I'm going off my memory of the GURPS 4E rules, but I believe you sum up the targets HP and twice DR (once for going in and once for going out) and subtract that from the damage. If the result is positive, the projectile has gone completely through the target, and it might hit and do damage to something directly behind the original target. You can keep doing this until you run out of damage or potential targets.

Unknown said...

@Chauncey: Doesn't sound bad, your system. Witty to concider also exit wound, as there is also armor as in front. Good point.

I'd like to keep my game as simple as possible without forgetting the "game" part of it. I try to keep calculating in minimum (for example better or worse situations aren't affecting as increase or decrease to target number).

Thanks for sharing!

Unknown said...

@Granger44: Now as you say it, I recall reading rules for example shooting through car door for example.

I try to keep this example. There is a bit calculating in my idea, but I think it is simple.

Darn! I didn't write my idea of penetration here! I commented, as I had, but posting same things in forum same time makes my head confuzzled.

Next post -> my idea for armor penetration!

Shimoroka said...

What forum have you posted on?

I've been looking at your YDIN system. I'm not quite sure how you are planning to use them but your secondary attributes for Wounds and Health reminds me of a first edition system a friend conceived for his space opera RPG.

He had Health Points and Vitality Points. Vitality represented the consciousness or how much of a pulp a character is beaten to and Health represented core life such as bullet holes, deep cuts, missing limbs, burns. Health/Vitality with Endurance (physical resistance) aided a lot in keeping characters' tough and always in the fight.

Your over/under for rolls works to make characters stay in the action. And that's why Wounds/Health reminded me of my friend's system.

Maybe have a portion on the character sheet like AC in DnD that is the pre-calculated "Penetration", in YDIN it might be Stamina+Armor (while not forgetting if there is protection on the exit side). In GURPS it's based on HP but I think Constitution or in YDIN's case, Stamina, (a character's toughness) is a more logical choice.

Unknown said...

I mainly use (finnish).

You can find YDIN stuff here:

I like my over/under. It certainly keeps characters in action. Even if your character sucks, you don't spend game time failing all the time... with over roll you might fail, but hey, you might success when you normally wouldn't. I want every character to have a change to do stuff, difference is, that better characters don't dramatically fail so often than those who "act out of luck".

Well, "penetration" is same as wounds so you don't basically need another value for it. And armor decreases damage in general.

I haven't done character sheet yet (well, I have character sheet but not any publishable version) so I think it could clear things out. Actually in new rpg's I get first thing I check out is the character sheet.

Thankies for comments!