David L. Pulver Tue, 16 Sep 1997 22:21:58 -0400 (EDT) Customized Ammo in GURPS Vehicles 2nd Edition By David L. Pulver Tarnation!, Sam Colt cursed. "Here I am, trying to build myself a pistol that fires the same cartridge as the trusty Winchester '73 rifle. But those cursed GURPS Vehicles rules won't let me build one -- they've made the assumption that shorter barrels always mean shorter cartridges. How can I build my patented Colt 0.45 Peacemaker under these damned rules?" "To say nothing of modern weapons like the CAR 15, which uses the same cartridge as the M16, but in a carbine-format weapon with a radically chopped down barrel," the game designer agreed humbly. "You're up the creek without a paddle if you try to build one of these. But don't worry - -- help is on the way." GURPS Vehicles 2nd Edition makes the playable assumption that conventional-ammunition weapons with longer barrels will fire more powerful ammunition. However, this is not always the case in real life. Examination of the Weight Per Shot tables (p. VE108) shows there are three broad categories of rounds for each of small arms and cannon: ordinary rounds, low powered rounds, and extra-low powered rounds. As the "L" factor on the table hints, these are implicitly divided into three subcategories that depend on barrel length. They are: rounds fired by very or extremely-long barrel weapons (we'll call these "very long" rounds), rounds for medium or long barrel weapons (we'll dub them "long rounds") and rounds for weapons with short to extremely short barrels ("short rounds"). Thus, any round of ammunition can now be described by bore size (e.g., 7.62mm), by power (normal, low or extra-low), and by length (short, long or very long). You can skip length from the description unless you design the weapon to fire a shorter or longer round than usual for its barrel type. If you do, these special rules apply . . . Short Rounds These are normally fired by weapons with extremely short to short barrels. If a weapon with a medium or longer barrel is designed to fire short rounds, add "short round" to the weapon and ammo description and modify the design procedure as follows: With Medium or Long Barrel: For KE damage, subtract 0.075 from L. For 1/2D range, subtract 0.085 from L. For Weight, subtract 0.1 to L. For WPS and recoil, treat as a short barrel. With Very or Extremely Long Barrel: For KE damage, subtract 0.15 from L. For 1/2D range, subtract 0.16 from L. For Weight, subtract 0.225 to L. For WPS and recoil, treat as a short barrel. Long Rounds Normally fired by weapons with medium or long barrels. If a weapon with a different barrel length is built to fire long rounds, add "long round" to the weapon and ammo description and modify the design procedure as follows: With Extremely Short to Short Barrel: For KE damage, add 0.075 to L. For 1/2D range, add 0.085 to L. For Weight, add 0.1 to L. For WPS and recoil, treat as short barrel. With Very or Extremely Long Barrel: For KE damage, subtract 0.075 from L. For 1/2D range, subtract 0.085 from L. For Weight, subtract 0.125 from L. For WPS and recoil, treat as long barrel. Design Tip: If you want to build various "magnum" or "hotload" pistols, try using an extremely short or very short barrel, a low powered weapon, and a "long" round. Very Long Rounds Normally fired by weapons with very long and extremely long barrels. If a weapon with a shorter barrel length is designed to fire a very long round, add "very long round" to the weapon's and ammo's description, and modify the design procedure as follows: With Extremely Short to Short Barrel: For KE damage add 0.15 to L. For 1/2D range, add 0.16 to L. For Weight, add 0.225 from L. For WPS and recoil, treat as very long barrel. Optionally, increase chance of malfunction by one step. With Medium or Long Barrel: For KE damage and 1/2D range, add 0.075 to L. For Weight, add 0.125 to L. For WPS and recoil, treat as very long barrel. Design Tip: assault carbine weapons like Bushmaster or CAR 15 are probably best simulated with medium barrel and very long round.