Bigger guns & crossbows

[Hide]

Hello!

I am looking for the rules to make bigger guns and crossbows; think of a SM+1 Colt or Repeating Crossbow.

Any ideas? Thanks!

[mr beer]

Low Tech has plenty of artillery, including some crossbow-type weapons.

[Tyneras]

If you are interested in very detailed rules, then Pyramid #3/33 has the article The Deadly Spring. It gives detailed rules for building a bow or crossbow as well as ammunition from a wide variety of materials in any size or strength desired. It is very math heavy, but comes with a handy spreadsheet.

[Fred Brackin]

Originally Posted by Hide

Hello!

I am looking for the rules to make bigger guns and crossbows; think of a SM+1 Colt or Repeating Crossbow.

Any ideas? Thanks!

Um, Colt _what_? M1911A1 in.45 ACP? Colt 1873 SAA in .45 Long Colt? Colt R75 in 30-06?

The major difference in subsonic pistols that become 1.5x larger is going to be the shift from P+ to P++. If you jsut make the bullets larger without increasing velocity you're going to not get much increased penetration.

A bullet 1.5x in every dimension is 3.75x as heavy leading to a proportional increase in KE. However there's a square root in Gurps damage so you only get a 1,94x increase in damage dice. Except that comes with a 2.25x increase in the frontal surface area of the bullet so that cancels out (and a little more) the increase in KE in penetration. The bullet will still do more tissue damage because of the increae to P++ but it won't be better at penetrating armor.

You'd be better off increasing velocity without increasign size. 1.5x velcoity is 2.25x KE but it's not washed out by an increase in frontal surface area so after the square root you get a straight 1.5x increase in damage dice.

So make your giganto-pistol with a 7 or 8 inch barrel and use a 50% longer magazine with a double-stacked column. That could get you about 3x as many rounds per mag.

[Hide]

Great! Thanks for your suggestions, I am checking them right now. By the way, a friend also told me about GURPS Low Tech Companion 2. It features an guide about modifying the size of weapons, the examples focus on melee weapons. But could this also work for missile weapons?

[AlexanderHowl]

Damage is proportional to the velocity times the HP of a projectile (which is related to the cube root of the mass of the projectile, which is 3.375x as much for a 50% increase, resulting in a cube root of 1.5x). Presumably, +1 SM would allow a pistol round to go from .40 to .60, which would increase the damage by 50% (the total energy increases by 3.375x). Honestly, it is probably more energy efficient to make faster bullets rather than larger bullets, but the speed of the projectile is sharply limited by the velocity of the gases pushing it out of a barrel.

[Hide]

Alright, considering the physics of guns you have laid on the table, I think I’ll just get bigger (already existing) guns, instead of turning small ones into their “giant versions”.

For crossbows the deadly spring is very good material.
But how do I add a magazine to a crossbow?
How would you turn (for example) the st8 crossbow into a repeating crossbow?

[clu2415]

What TL are you working with? Poorer materials at TL5 mean less ridiculous handgun rounds like .454 Casull or .50 AE. The increased weight of the weapon and the strength of the user would decrease recoil by one or two.

For higher ST crossbows and repeating crossbows, check out Low Tech. Bows and crossbows have a rated ST, that is, the force it launches with and requires to reload. The ST in the table is the ST necessary to hold and aim it properly. A pitiful human needs to involve their feet or a mechanical aid to draw a ST 15 crossbow—but a ST 15 giant could hold it against their shoulder and cock it with two hands! The giant can spend 2 seconds drawing, one second pulling out a bolt, and one second placing the bolt; A human would need 8 seconds or more to do all that.

[Fred Brackin]

Originally Posted by clu2415

What TL are you working with? Poorer materials at TL5 mean less ridiculous handgun rounds like .454 Casull or .50 AE.

.

There's no smokeless powder at TL5 anyway. You probably can't duplicate the ballistics of those rounds with black powder.

[clu2415]

Originally Posted by Fred Brackin

There's no smokeless powder at TL5 anyway. You probably can't duplicate the ballistics of those rounds with black powder.

That’s what I mean. Those would be the perfect rounds to build a bigger handgun for, but there’s no low tech equivalent.