GURPS ULTRATECH ballistics?

[DouglasCole]

I'll get back to this in an hour or so; dinnertime now.

[hal]

Originally Posted by DouglasCole

I'll get back to this in an hour or so; dinnertime now.

Thanks Doug.

I'm looking at your formulas for the EASY CONVERSIONS tab, and for the most part, I suspect that this is what I was originally looking at when I first made my spreadsheet.

Now, I'm looking at another formula that lists the formula of Muzzle energy as being equal to:

Muzzle Energy in J = Projectile Mass(g) x (velocity in m/sec)^2/2011

I was trying to figure out why the 2011 constant for the divisor was there, until I spotted the formula where Velocity in meters per second was spelled out. This formula works out to:

Velocity in m/sec = (Muzzle Energy(J)/Projectile Mass(in grams))^.5 x 44.84

When I factored out the various things, I came to realize the 2011 value is actually the 44.84 value squared (but rounded off). Even so, the two formulas that I'm looking at for Muzzle Energy in Joules (yours and Greg's) are off by about .528 percent (ie, negligible really).

More in my next post...

[hal]

Ok, so I decided to try an analyze the different approaches to damage values, muzzle velocity, Joules per gram of a given substance etc - all the while using both GUNS, GUNS, GUNS by Greg Porter and the spreadsheet that you devised, along with the formulas for what I used in order to that I could use specific real world data of bullet weight in Grains and bullet velocity in feet per second (how the data is displayed in CARTRIDGES OF THE WORLD 8th edition - I know it is at a higher edition than 8th as of today!).

So, here's what I did. I used both of Greg's formulas - Muzzle Velocity and Muzzle Energy, to double check against each other, and the original real values for any given bullet (the one I listed earlier with a bullet mass of 130 grains and a bullet velocity of 1180 feet per second).

Using your formula given on your spreadsheet, the Muzzle Energy for a 130 grain bullet travelling 1180 feet per second works out to 544.8475086 Joules. Greg Porter's formula gives a value of 541.9681402 Joules.

Using only Greg's formula for Muzzle Velocity (I didn't try to reverse engineer your formula, but I'd imagine if I did reverse engineer your formula, it would be slightly different than Greg's formula)...

(544.8475086/8.4238583)^.5 x 44.84 = 360.6181343 Meters per second or 1183.1304 Feet per second.

Using Greg's calculation formula for Joules in the equation:

(541.9681402/8.4238583)^.5 x 44.84 = 1180

So, it isn't surprising that using only Greg's formulas for Muzzle Velocity and Muzzle Energy will be internally self-consistent in order to double check things.

Your formula for Joules is:

.5 * Weight in grams/1000 * (Velocity in meters/sec divided by 1000)^2

I'm guessing that you were trying to use the formula such that it used unit measures of Kg and Kilometers

That's my guess overall.

[DouglasCole]

Originally Posted by hal

Your formula for Joules is:

.5 * Weight in grams/1000 * (Velocity in meters/sec divided by 1000)^2

I'm guessing that you were trying to use the formula such that it used unit measures of Kg and Kilometers

That's my guess overall.

You sure that second m/s is divided by 1000? A Joule is a kg m/s^2, which is mass in kg, velocity in m/s. There shouldn't be a second divisor there.

[hal]

Originally Posted by DouglasCole

You sure that second m/s is divided by 1000? A Joule is a kg m/s^2, which is mass in kg, velocity in m/s. There shouldn't be a second divisor there.

Double checking...

130 grain bullet is 8.4238583 grams
.38 inch Diameter is 9.652mm
1180 feet per second is 359.6639885 meters per second

Plugging the same data into your spreadsheet, and then looking at your "used column" (Column F in the Excel spreadsheet titled as Ballistics Model Jan1 - 2012)

Grains 130 - used .008424 kg
Inches .38 - used .009652 m
FPS 1180 - used 359.664 m/s

Your formula for Joules lists the formula =0.5*D3*D6^2 where D3 is Kg, D6 is M/s

Sorry - was correct on one, incorrect on the other...

Only the one is divided by 1,000 to get it into units of Kilograms. The meter's per second is not km per second... (bad Hal, no cookies for you!)

[hal]

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 27-7 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. :(

[Fred Brackin]

Originally Posted by hal

2.72 grams for a 7.5mm round seems AWFULLY low. :(

Ammo weights might be the most hashed up numbers in UT. I doubt you can do anything sensible with them.