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Old 04-07-2012, 02:19 PM   #1
Landwalker
 
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Default [HT] Statting a Firearm

In a fit of foolhardy restlessness, I've started trying to lay the groundwork for a new campaign of the contemporary and reasonably realistic sort, based largely on Jagged Alliance 2.

To that end, I plan / expect to be throwing together stats for a pretty large chunk of stats that aren't in High-Tech, Pulp Guns, Gun-Fu, or Tactical Shooting, simply because I can never get a large enough selection of toys. A ludicrously vast array of options is my happy place.

So I nipped over here and picked up Douglas Cole's spreadsheet, and have decided to take it for a test run using the Beretta Cx4 Storm carbine in 124gr 9x19mm Parabellum.

Since I know all of jack and squat about the technical side of firearms in real life, I present my work to the hive mind for review in order to make sure I did everything properly, didn't bugger it all up, and got reasonable results considering the weapon in question.

Inputs
From what I can tell, this section is almost entirely from the "Cartridge Stats" sheet, with the only exception being Barrel Length, which I entered as 422.5 millimeters (16.6 inches). Everything else is straight out of the 124gr 9x19mm column on Cartridge Stats.

Aaand that's pretty much it!
Outputs
Armor Penetration: 3d+0

Normal Damage, JHP Damage, and Fragment Damage: I'm not really sure what these lines mean, but they are respectively 3d+0 {1.4}, 2d+2 {1.8}, and 3d+0 {1.6}. AP Damage is 3d+0 {0.98}. No idea what the numbers in braces are for on any of this.

Weapon Weight: Somehow, this is "#N/A", which seems to be caused by the "Action Type" selector. The spreadsheet's default is "Auto," but if you open the drop-down menu, you get a bunch of very small numbers instead. I had no idea what to do with that. Also seems like I can just take weight straight off the official page anyway, so I'm doubly confused.

Range: Max 2,090. I assume this is in yards? Seems like a pretty reasonable number to me, about on part with the Winchester M1 Carbine (HT.120). The lower table gives what I assume to be a D Range of 260 yards, which again seems reasonable for the weapon in question.
And that's about all I can figure out. Determining weight is easy enough from known specifications, RoF is 3 (Semiautomatic), Shots is straight-forward, and I suppose ST, Bulk, and Rcl are pretty much just "best estimates."

So, thoughts? Input? Corrections? Ridicule?

Last edited by Landwalker; 04-07-2012 at 02:24 PM.
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Old 04-07-2012, 02:27 PM   #2
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Default Re: [HT] Statting a Firearm

Quote:
Originally Posted by Landwalker View Post
In a fit of foolhardy restlessness, I've started trying to lay the groundwork for a new campaign of the contemporary and reasonably realistic sort, based largely on Jagged Alliance 2.
Awesome! I do love those games. They remind me of X-COM, another of my old flames...

Quote:
Normal Damage, JHP Damage, and Fragment Damage: I'm not really sure what these lines mean, but they are respectively 3d+0 {1.4}, 2d+2 {1.8}, and 3d+0 {1.6}. AP Damage is 3d+0 {0.98}. No idea what the numbers in braces are for on any of this.
The numbers in braces are alernate Wound Modifiers, to replace the normal pi- through pi++. So a solid bullet deals 3d and multiplies penetrating damage by 1.4, Hollow Point deals 2d+2 times 1.8, etc. If you want to use the normal piercing modifiers, I suggest just rounding normal damage to the closest one, and basing the rest on that as normal. So Normal deals pi+, HP deals pi++, AP deals pi, etc. Not sure what Fragment signifies, though.
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Old 04-07-2012, 02:42 PM   #3
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Default Re: [HT] Statting a Firearm

Quote:
Originally Posted by Landwalker View Post
Range: Max 2,090. I assume this is in yards? Seems like a pretty reasonable number to me, about on part with the Winchester M1 Carbine (HT.120). The lower table gives what I assume to be a D Range of 260 yards, which again seems reasonable for the weapon in question.
Unfortunately that last time I checked the 1/2D Range stat on that spreadsheet is not consistent with GURPS (apparently 1/2D range is still something of a legacy mechanic, not quite the range at which the bullet has dropped to 1/2 its energy). There aren't any official SMGs with barrel lengths that long published but I doubt 1/2D would be more than 200 yards.

For example the spreadsheet gives even a 20mm barrel the same 1/2D range.

Last edited by lexington; 04-07-2012 at 02:49 PM.
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Old 04-07-2012, 02:47 PM   #4
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Default Re: [HT] Statting a Firearm

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Originally Posted by vierasmarius View Post
The numbers in braces are alernate Wound Modifiers, to replace the normal pi- through pi++. So a solid bullet deals 3d and multiplies penetrating damage by 1.4, Hollow Point deals 2d+2 times 1.8, etc. If you want to use the normal piercing modifiers, I suggest just rounding normal damage to the closest one, and basing the rest on that as normal. So Normal deals pi+, HP deals pi++, AP deals pi, etc. Not sure what Fragment signifies, though.
Ah. I thought they might be something like that, but wasn't sure.

But if I were going to use the RAW wounding modifiers (and I intend to), why wouldn't it just be pi? That's what everything else that uses 9x19mm has.

Quote:
Originally Posted by Lexington
There aren't any official SMGs with barrel lengths that long
Well, that's makes sense, as the Cx4 isn't an SMG, but rather a semiautomatic carbine that happens to use a pistol-caliber round. That said, I don't expect the Cx4 to have a D range comparable to any proper modern rifles—it's considerably shorter even than the M1 carbine, and nowhere near anything else, but I wouldn't be shocked if it still got knocked down a bit. 260 does strike me as potentially a bit high.
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Old 04-07-2012, 02:49 PM   #5
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Default Re: [HT] Statting a Firearm

Quote:
Originally Posted by Landwalker View Post
Weapon Weight: Somehow, this is "#N/A", which seems to be caused by the "Action Type" selector. The spreadsheet's default is "Auto," but if you open the drop-down menu, you get a bunch of very small numbers instead. I had no idea what to do with that. Also seems like I can just take weight straight off the official page anyway, so I'm doubly confused.
There used to be a semi-functional weapon design part of the sheet, but it's defunct. Just use the real stats and ignore this.

Quote:

Range: Max 2,090. I assume this is in yards? Seems like a pretty reasonable number to me, about on part with the Winchester M1 Carbine (HT.120). The lower table gives what I assume to be a D Range of 260 yards, which again seems reasonable for the weapon in question.[/indent]
My 1/2D ranges work pretty well for strongly supersonic projectiles, but less well for subsonic ones and pistol bullets.
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Old 04-07-2012, 02:51 PM   #6
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Default Re: [HT] Statting a Firearm

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Originally Posted by Landwalker View Post
But if I were going to use the RAW wounding modifiers (and I intend to), why wouldn't it just be pi? That's what everything else that uses 9x19mm has.
True. Presumably the wounding calculations Douglas Cole used involves some combination of calibre and velocity, and GURPS doesn't take velocity into account except to distinguish between 4-8mm pistol and rifle rounds. Calling it pi would be consistent with RAW firearms, which is makes sense if you aren't planning on recalculating all the guns from HT.
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Old 04-07-2012, 02:51 PM   #7
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Default Re: [HT] Statting a Firearm

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Originally Posted by lexington View Post
Unfortunately that last time I checked the 1/2D Range stat on that spreadsheet is not consistent with GURPS
Yep. It looks at the dimensions of the cartridge (sectional density, length, aspect ratio) and figures out how velocity decays.

Quote:
For example the spreadsheet gives even a 20mm barrel the same 1/2D range.
But that's exactly right! The range at which the BULLET falls to half the INITIAL damage won't change that much unless you also have more sophisticated assumtions for how velocity falls off above and below the speed of sound.
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Old 04-07-2012, 02:53 PM   #8
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Default Re: [HT] Statting a Firearm

Quote:
Originally Posted by Landwalker View Post
Well, that's makes sense, as the Cx4 isn't an SMG, but rather a semiautomatic carbine that happens to use a pistol-caliber round. That said, I don't expect the Cx4 to have a D range comparable to any proper modern rifles—it's considerably shorter even than the M1 carbine, and nowhere near anything else, but I wouldn't be shocked if it still got knocked down a bit. 260 does strike me as potentially a bit high.
Being called a pistol carbine doesn't increase its range. It doesn't fire a special kind of bullet and nothing I've found suggests that it gets the bullet moving extremely fast (which actually shouldn't alter the 1/2D range, because it won't change the Ballistic Coefficient, but does in GURPS).
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Old 04-07-2012, 02:55 PM   #9
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Default Re: [HT] Statting a Firearm

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Originally Posted by vierasmarius View Post
True. Presumably the wounding calculations Douglas Cole used involves some combination of calibre and velocity, and GURPS doesn't take velocity into account except to distinguish between 4-8mm pistol and rifle rounds. Calling it pi would be consistent with RAW firearms, which is makes sense if you aren't planning on recalculating all the guns from HT.
Yes, for simplicity you just want to use pi.

I would honestly use the "AP Damage" line {0.98} for nearly all pistol bullets. It corresponds very well with the pi/pi-/pi+ in that range.

The wound channel modifiers basically are a function of something like the sqrt of a momentum term divided by a KE term (or something related to it; the equations are in the spreadsheet or my article itself).

The JHP line, however, does work out pretty well. It decreased penetration based on the increased frontal area of a squashed projectile, but INcreases wounding for the same reason. Works out decently.

The "normal damage" line looks at wounding when the bullet turns sideways a bit and is probably more correct for rifles with aspect ratio of 3-5 than it is for pistols.
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Old 04-07-2012, 03:33 PM   #10
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Default Re: [HT] Statting a Firearm

So for the final stat line, I'm looking at something like this:

Beretta Cx4 Storm, 9x19mm Parabellum
Damage: 3d pi
Acc...: 4 (on par with the longest-barreled SMGs)
Range.: 180/2,090 (I went with Lexington's comparison to the longest-ranged SMGs and just made it comparable to those. This also puts it only just past the Beretta 92F.)
Weight: 5.7/0.5 (loaded magazine weight is taken from the basically-identical Beretta 92F magazine on HT.101)
RoF...: 3
Shots.: 15+1 (3)
Bulk..: -4
Rcl...: 2
Cost..: Whatever I want it to be
LC....: 3
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