Steve Jackson Games - Site Navigation
Home General Info Follow Us Search Illuminator Store Forums What's New Other Games Ogre GURPS Munchkin Our Games: Home

Go Back   Steve Jackson Games Forums > Roleplaying > GURPS

Reply
 
Thread Tools Display Modes
Old 02-06-2020, 09:30 AM   #1
Michael Thayne
 
Michael Thayne's Avatar
 
Join Date: May 2010
Default TL 5-8 firearms in Ultra-Tech calibers

For the post part, Ultra-Tech conspicuously does not use calibers that are popular in the real world. Instead, it mostly uses calibers that make nice round numbers in the metric system: 5mm, 7mm, 10mm, 15mm. This got me wondering: in a universe where these calibers were standard, what stats would lower-tech firearms using those calibers have? You can imagine a variety of reasons why people would create such weapons, from colonists who are mostly TL9 but don't have a full-blown TL9 industrial base, to post-apocalyptic survivors making 10mm black-powder weapons because the metric system is the only system of measurement they know.

Looking carefully at various weapons tables, for TL7-8 weapons firing cased ammo I think the main difference is that they'll hold about 1/3 as many shots as their TL9 equivalents. Damage is AFAICT likely to be unchanged—for example both High-Tech and Ultra-Tech rifles generally seem to inflict dice of damage equal to about 90% of their caliber in millimeters. Other stats seem mostly to be similar—though Ultra-Tech guns also seem to have slightly lower ST requirements on average for reasons that aren't entirely clear to me (ergonomics?). Maybe lower-tech equivalents to Ultra-Tech guns would have as much as +2 to ST requirements, though that seems to produce too-high ST requirements in some cases. Maybe only +1.

Much less certain about post-apocalyptic guns using round millimeter calibers but I'm open to suggestions.
Michael Thayne is offline   Reply With Quote
Old 02-06-2020, 10:16 AM   #2
clu2415
 
Join Date: Jun 2016
Default Re: TL 5-8 firearms in Ultra-Tech calibers

Lower strength requirements can come from more aerodynamic bullets. At lower tech levels, you take a big bullet and put a bunch of powder behind it to fling it with brute force. With advanced aerodynamic modeling, you can design bullets that lose much less energy to drag, thus dealing the same damage at the same distance, but with lighter ammunition and less recoil.

One of the major obstacles is chamber pressure. Newer calibers operate at much higher pressures, so building a lower-tech firearm that can handle that pressure could be tricky. You’ll see a major reduction in accuracy due to low tech manufacturing having much less precision and repeatability.
clu2415 is offline   Reply With Quote
Old 02-06-2020, 11:38 AM   #3
Ulzgoroth
 
Join Date: Jul 2008
Default Re: TL 5-8 firearms in Ultra-Tech calibers

If you look at the numbers, they aren't actually that weird.

5mm and 7mm are obviously truncations of the most common modern rifle calibers. The reduction isn't negligible, but it's only around 10%. I'd be surprised if you could find those in black powder, I'd think something so small would work terribly without smokeless (EDIT: actually, 7mm I guess you could, weren't the first ones smokeless adaptations of final-generation black powder cartridges?). 10mm is an actual modern pistol caliber, similar to some other modern pistol calibers, and also a close match to some big-game rifle calibers (which go back to the 19th century and carry forward to the present). 15mm is square-on for the caliber of US Civil War era rifle-muskets (the Springfield and Enfield anyway) and very close to the heavy soviet 14.5mm HMG/AMR caliber.
__________________
I don't know any 3e, so there is no chance that I am talking about 3e rules by accident.
Ulzgoroth is offline   Reply With Quote
Old 02-06-2020, 12:28 PM   #4
newton
 
Join Date: Oct 2018
Default Re: TL 5-8 firearms in Ultra-Tech calibers

Quote:
Originally Posted by Ulzgoroth View Post
If you look at the numbers, they aren't actually that weird.

5mm and 7mm are obviously truncations of the most common modern rifle calibers. The reduction isn't negligible, but it's only around 10%. I'd be surprised if you could find those in black powder, I'd think something so small would work terribly without smokeless (EDIT: actually, 7mm I guess you could, weren't the first ones smokeless adaptations of final-generation black powder cartridges?)
Actually on 7mm i would bet that its more of a standin for 6.8 or 6.5 mm rifles, which is intended as an intermidiate between 7.62 and 5.56. a relatively safe bet as the army had a program intended to replace the m16 with gun firing a bigger bullet twice so far iirc
newton is offline   Reply With Quote
Old 02-06-2020, 01:20 PM   #5
copeab
 
copeab's Avatar
 
Join Date: Mar 2005
Location: near Houston
Default Re: TL 5-8 firearms in Ultra-Tech calibers

The 1871 Mauser and 1873 Springfield Trapboor used 11+mm ammunition.

The 7mm Mauser cartridge gained some popularity in the 1890's and was available instead of 8mm (7.92mm) that was most common for Mauser rifles.
__________________
A generous and sadistic GM,
Brandon Cope

GURPS 3e stuff: http://copeab.tripod.com
copeab is offline   Reply With Quote
Old 02-06-2020, 02:04 PM   #6
Kale
 
Kale's Avatar
 
Join Date: Aug 2005
Location: Cowtown, Canada
Default Re: TL 5-8 firearms in Ultra-Tech calibers

It's interesting how even with metric 'labeled' cartridges you get odd numbers. What was the 7.92mm based on? Did some armorer have a random stick lying around and that happened to be the size he used for the bore of the prototype? I can understand 'customary' unit to metric conversions, which is where 7.62mm comes from, but is that always how non-integer metric calibers come to be?
Could be interesting as a campaign flavor detail: "bullet size was the diameter of the spear shaft of the first emperor's imperial guards" or something quirky like that.
__________________
FYI: Laser burns HURT!
Kale is offline   Reply With Quote
Old 02-06-2020, 02:27 PM   #7
Ulzgoroth
 
Join Date: Jul 2008
Default Re: TL 5-8 firearms in Ultra-Tech calibers

Oh, 15mm was also used as the original caliber for the German MG 151 (the 20mm version was more widely used), and an inter-war Czech infantry HMG that was adapted and produced in Britain during WWII.
__________________
I don't know any 3e, so there is no chance that I am talking about 3e rules by accident.
Ulzgoroth is offline   Reply With Quote
Old 02-06-2020, 05:43 PM   #8
Rupert
 
Rupert's Avatar
 
Join Date: Aug 2004
Location: Wellington, NZ
Default Re: TL 5-8 firearms in Ultra-Tech calibers

7mm is a common hunting calibre, as is ".270", which is very close to 7mm, and 7mm military rounds were once quite common too. While Germany went with the 7.92mm/8mm Mauser, 7x57mm Mauser was a very common military round in the rest of the world for much of the early 20th century. Which is to say, 7mm is actually a common rifle calibre, especially outside the USA.
__________________
Rupert Boleyn

"A pessimist is an optimist with a sense of history."
Rupert is offline   Reply With Quote
Old 02-06-2020, 06:03 PM   #9
Agemegos
 
Agemegos's Avatar
 
Join Date: May 2005
Location: Oz
Default Re: TL 5-8 firearms in Ultra-Tech calibers

Quote:
Originally Posted by Kale View Post
It's interesting how even with metric 'labeled' cartridges you get odd numbers. What was the 7.92mm based on?
Ooh! I know that one! 7.92 mm is 0.3 Zolle, where one Zoll is a twelfth of a Fuß. The English weren't the only people to have a bewildering mess of customary units before adopting metric!
Quote:
Did some armorer have a random stick lying around and that happened to be the size he used for the bore of the prototype? I can understand 'customary' unit to metric conversions, which is where 7.62mm comes from, but is that always how non-integer metric calibers come to be?
The same question has often puzzled me with respect to Imperial and US units. Why .357 magnum? Why .303 British? Why .276 Enfield? Why .455 Webley? Why .338 Lapua magnum? Why .351 Winchester? Why .454 Casuli?
__________________

Decay is inherent in all composite things.
Nod head. Get treat.

Last edited by Agemegos; 02-06-2020 at 06:14 PM.
Agemegos is offline   Reply With Quote
Old 02-06-2020, 06:18 PM   #10
Sam Cade
 
Sam Cade's Avatar
 
Join Date: Jan 2005
Location: Down in a holler
Default Re: TL 5-8 firearms in Ultra-Tech calibers

Quote:
Originally Posted by Kale View Post
but is that always how non-integer metric calibers come to be?
Some the oddities come from rounding, some of it comes from whether or not the bore is measured from the grooves or lands.
__________________
Doin' what I can with what I got.-Burt Gummer

http://www.jpfo.org/
كافر
Sam Cade is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Fnords are Off
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 04:33 PM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2024, vBulletin Solutions, Inc.