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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

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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 02-06-2020, 02:27 PM   #7
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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.
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Old 02-06-2020, 05:43 PM   #8
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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.
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Old 02-06-2020, 06:03 PM   #9
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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?
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Old 02-06-2020, 06:18 PM   #10
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Default Re: TL 5-8 firearms in Ultra-Tech calibers

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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.
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