04012017, 07:32 PM  #11 
Join Date: Aug 2004
Location: Buffalo, New York

Re: GURPS ULTRATECH ballistics?
Assuming a 7.5mm caseless round, that weighs 110 grains, its velocity must be 1470 feet per second in order to inflict 2d6+2 damage.
GURPS has the ammunition weighing roughly .006 lbs per shot. This measures approximately 2.72 grams Hmmm. That stinks! .06 lbs per round would be 27.2 grams  subtracting 7.13 grams for the bullet, the propellent would weigh 277 or 20 grams. Does 20 grams to produce 750 Joules of energy sound realistic? That works out to 37 joules per gram? Hmm. Just had a 'how much do you love your wife and daughter moment asking for ice cream. Time for me to bail out until later... One thing for sure is... 2.72 grams for a 7.5mm round seems AWFULLY low. :( 
04012017, 07:41 PM  #12 
Join Date: Aug 2007

Re: GURPS ULTRATECH ballistics?
Ammo weights might be the most hashed up numbers in UT. I doubt you can do anything sensible with them.
__________________
Fred Brackin 
04012017, 08:03 PM  #13 
Join Date: Oct 2008

Re: GURPS ULTRATECH ballistics?
The rifle rounds look close to reasonable actually, but the pistol rounds are silly low weight. Apparently all UT pistol rounds are lightweight plastics or similar for some strange reason..

04012017, 08:09 PM  #14 
Join Date: Feb 2005
Location: Berkeley, CA

Re: GURPS ULTRATECH ballistics?
Pretty sure that doesn't work once the expansion rate is significant relative to the speed of sound in the gas; ideal gas law is for equilibrium.

04012017, 08:17 PM  #15 
Join Date: Feb 2005
Location: Berkeley, CA

Re: GURPS ULTRATECH ballistics?
The issue isn't as much weight as there being clips that are lighter than the ammunition they contain.

04012017, 08:37 PM  #16  
Join Date: Oct 2008

Re: GURPS ULTRATECH ballistics?
Quote:
Today the lightest 10mm bullets commonly used are about 135 grains, with something like 155180 grains being more normal(and some bullets being 200 grains), then add the propellant to that and the UT total seems... very low in comparison. 

04012017, 08:51 PM  #17 
Join Date: Aug 2004
Location: Buffalo, New York

Re: GURPS ULTRATECH ballistics?
OK, the numbers for real world damages look like they're pretty good, which means that for conventional firearms in an UT world, they should work as well.
After hitting GURPS CLASSIC MODERN FIREPOWER, the stats for the 4.73 Caseless Telescoped Ammunition indicate that it weighs .011 pounds per round, which works out to be roughly almost 5 grams in weight. Damage for the round is listed as being 4d6+2. Real world data suggests a muzzle velocity of 930 meters per second. The overall weight of the bullet is 3.25 grams. It would appear that the remaining 1.73 grams of weight is the actual propellant. At 930 meters... that's about 3051 feet per second. Ok, filling in those values for the spreadsheet, I end up with 3d6+2 damage (50 grains bullet weight, 3051 feet per second velocity). GURPS HIGH TECH for 4e shows that the assessed damage is still what it was in GURPS CLASSIC Modern Firepower: 4d+2. Either Hans had his reasons for bumping up the average damage value by a full 3.5 points, or he didn't have access to this spreadsheet when he compiled the damage (or some other possibility that I've not considered). In any event, the propellant weight of 1.73 grams will produce roughly 1401 Joules of energy. This works out to be roughly 809.8 joules of energy per gram of propellant. This presumes of course, that the full energy available is 100% utilized, which I suspect is not the case, but it gives me a useful approximation of what should be the situation. Now, Lead has a specific gravity of 11.34 grams per cubic centimeter? With a mass of 3.25 grams, the volume of the bullet is about .28 cubic centimeters. If the density of the propellant materials is close to that of water, then the volume of propellant is roughly 1.73 cubic centimeters to the .28 cubic centimeters of the round itself. That's roughly a 6;1 volume ratio for the propellant to projectile. so, let's reexamine the UT 7.5mm round. Clearly, a 110 grain round is a bit much, since a 4.73 round is only 50 grains. What would be a valid bullet weight for a 7.5mm round? Last edited by hal; 04012017 at 08:54 PM. Reason: Missed the word in blue that makes all the difference 
04012017, 09:03 PM  #18 
Join Date: Oct 2008

Re: GURPS ULTRATECH ballistics?
.32 ACP tends to use 6073 grain bullets, but something like 7.62×25mm Tokarev uses typically about 90 grain bullets, so it varies.

04012017, 09:36 PM  #19  
Join Date: Aug 2004
Location: Buffalo, New York

Re: GURPS ULTRATECH ballistics?
Quote:
Here is what I just tried to do for a pistol round of 90 grains with a 1650 feet per second statistic. The Calculated Muzzle Energy in Joules was 737 Joules and the damage was 2d6+2 per the description in ULTRATECH. On the presumption that 1 gram of modern day propellant used in the G11 round contains 809 joules of energy, I would need about .9 grams of propellant to propel a half gram bullet down range. Problem is, the original x6 volume of propellant required for the rifle round. Since this is a pistol round, the ratio of 6:1 is probably too high. Call it half that, and the ratio of 3:1 would result in roughly 1.5 grams of propellant. This in turn, would increase the joules value to a higher rating. So, let's say that the pistol uses a 3:1 ratio for propellant volume for pistols. 1.5 Grams of propellant is 1.5 x 809 Joules or 1213.5 Joules New round based on 3:1 ratio of propellant to projectile by volume  90 Grain bullet 2464 feet per second damage is 3d6+3 (average damage is 13.9 damage, which means it probably should be more like 4d+0 damage instead, or even 4d1 damage) bullet weight is .004 pounds per shot (it has some trailing digits after 4, but it never rounds upwards and I left it at that.). This was calculated with a bullet weight of .5 grams, and 1.5 grams of propellant to equal 2 grams per round or .004 something pounds per round). It would be safer to say that it takes 226 rounds to equal 1 pound in weight. Does this seem MORE reasonable to you overall? My question now becomes  what is the stopping power of the bullet in general? Seems like it is a small round, very light weight. What happens when it hits something like armor? Would it be less likely to penetrate, or more likely? THAT I couldn't answer, but it seems like there is a reason to make bullets heavier in weight for larger targets. One of the Remington rifle bullets discusses that the .3006 government round has different bullet weights depending on whether you're varmint shooting or game shooting. 100130 grain bullets for varmint hunting won't penetrate as well against bigger game. It is suggested 100 to 150 to 160 grain for midrange shooting, and 180, 200, or 220 grain for big game hunting. The flip side of this is, that we have a 3.25 gram bullet for the G11 round, and that's only 50 grain. One has to wonder if they would have found that round to be anemic against military targets or not (again, I don't know what the real life story is here, just musing in ignorance!) 

04012017, 09:45 PM  #20 
Join Date: Aug 2004
Location: Buffalo, New York

Re: GURPS ULTRATECH ballistics?
Anyone know how to calculate the recoil of the bullets we're discussing? A .45 colt black powder weapon has a Muzzle Energy in Joules of 500 plus change. A weapon with one that is a little over twice that of a .45 colt should have a recoil of what?
Oh, I was looking at the wrong column on my spreadsheet for the ME in Joules. I was trying to get that to 1213 when I played around with the need to have 1213 Joules for 1.5 grams of propellant. New damage is now: 3d+1 (Average damage is supposed to be 11.9) so maybe 3d+2? Oooops, but not a major one it seems. Bullet weight remains what I figured at 2 grams, and damage is about the same, just 1 pip less. So, anyone? How does one calculate the recoil statistic? Is it a factor of barrel length plus weapon weight or something along those lines? 
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