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Old 02-06-2020, 09:30 AM   #1
Michael Thayne
 
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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.
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Old 02-06-2020, 10:16 AM   #2
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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.
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Old 02-06-2020, 11:38 AM   #3
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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.
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Old 02-06-2020, 12:28 PM   #4
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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
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Old 02-06-2020, 01:20 PM   #5
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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.
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Old 02-06-2020, 02:04 PM   #6
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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.
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Old 02-07-2020, 12:56 PM   #7
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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%. <snip>
I don't know what counts as a "weird" caliber, but I don't think these calibers are mere stand-ins for their slightly larger real-world cousins. They seem to do about 10% less damage rather than just using stats for those common modern rifles. I'd be interested to see canonical stats for those 6.8mm or 0.27 in or whatever modern rifles.

For black powder weapons I wasn't suggesting having 5mm or 10mm examples, more like 10mm and 15mm versions of say the Kentucky rifle whose official stats in HT are for 0.45 in. I think higher calibers for spherical bullets should have longer range holding muzzle velocity constant due to a higher ratio of mass to cross-sectional area but I'm not certain.
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Old 02-07-2020, 04:58 PM   #8
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Default Re: TL 5-8 firearms in Ultra-Tech calibers

Quote:
Originally Posted by Michael Thayne View Post
I don't know what counts as a "weird" caliber, but I don't think these calibers are mere stand-ins for their slightly larger real-world cousins. They seem to do about 10% less damage rather than just using stats for those common modern rifles. I'd be interested to see canonical stats for those 6.8mm or 0.27 in or whatever modern rifles.
From HT:

7x57mm Mauser: 6d+2 pi
6.5x50mmSR Arisaka: 6d pi

About what you'd expect from a full-power military cartridge of the late 19th/early 20th century.
Quote:
For black powder weapons I wasn't suggesting having 5mm or 10mm examples, more like 10mm and 15mm versions of say the Kentucky rifle whose official stats in HT are for 0.45 in. I think higher calibers for spherical bullets should have longer range holding muzzle velocity constant due to a higher ratio of mass to cross-sectional area but I'm not certain.
They do. Also, the bigger the bore the less fouling affects the ability to load the weapon without cleaning it constantly.
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Old 02-07-2020, 05:16 PM   #9
Michael Thayne
 
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Default Re: TL 5-8 firearms in Ultra-Tech calibers

Quote:
Originally Posted by Rupert View Post
From HT:

7x57mm Mauser: 6d+2 pi
6.5x50mmSR Arisaka: 6d pi

About what you'd expect from a full-power military cartridge of the late 19th/early 20th century.
Good catches. I also found a 6.8mm weapon in Tactical Shooting. The 6.8mm weapon is TL8 and its stats are pretty darn close to the TL9 7mm weapon. Also, after more research it seems like the weight of a modern cartridge is generally around 50% brass, at most? Given that I might go with cased versions of TL9 caseless weapons halving half as many shots and otherwise being identical.
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