25 January 2018

Damn You Maths

GURPS: High Tech Adventure Guns gives stats for the M1892 rifle.  This is the 30" barreled standard rifle.

The 220 gr bullet zooming along at 2,000 feet per second from Wikipedia gives...

6d+1 pi and 1,000/3,900.

Plugging the numbers into Douglas Cole's formula gives...

6.12 dice or 6d pi.  A bit short of the 6.15 needed to get 6d+1, but since there's a 10% fudge factor... you can say 6.12 is anything between 5.51 and 6.74.

Rifles of the World 2e agrees with this bullet weight and velocity for the M1892 rifle.

A "factory load" for 220 gr is shown at 2,200 feet per second in Cartridges of the World 11th Edition under "current American rifle cartridges".  This is the spec for the .30 Army (.30-40 Krag) in Cartridges of the World 11th Edition under military cartridges as well.

6.76 dice or 6d+3 pi aka 7d-1 pi.  The fudge factor ranges between 6.08 and 7.43 or 6d and 7d+2.

Rifles of the World 2e says this matches "high velocity" ball ammunition introduced with the M1898 rifle.

Hmmmmm.

High Tech 4e p. 165 has Extra-Powerful (+P) Ammunition.  It's simply a 10% boost to damage, range and ST.

6d+1 plus 10% is 7d!  1,000/3,900 plus 10% is 1,100/4,290.  ST 10† plus 10% is 11†.  We're courting .30-06 stats here (7d+1 pi; 1,100/4,500; ST 9†).

Vehicles gives a range of 940/4,600 for either round because it's based on a bore/barrel length ratio.

Now the problem.

Remington says their ammunition specs are with a 24" barrel, same as my Krag.

180 gr bullet zinging out the muzzle at 2,430 feet per second.

Cole's formula gives 6.76 dice, just like the 220@2,200 round in a 30" barrel.

The vehicles range formula gives 790/4,200.  At least the shorter barrel has less range...

Nothing matches!

Douglas Cole's formula adhere well to the conventions of 3rd edition GURPS (revised).  I use the GURPS: Vehicles range formulas because Mr Cole wrote a completely new range system for his GURPS games.  GURPS: Vehicles is a 3e book, and the range numbers often did not match published numbers of other guns.

A huge hunk of the problem is along with the 4th edition GURPS gun stats were handed off to Hans Christian-Vortisch.  OK, that's not a problem, it's a new edition, new methods of figuring out the guns.

Maddeningly, many of the numbers match between 3e and 4e for lots of guns.  The only change being piercing replacing crushing for damage type.

So you end up fudging, a lot.

Since the modern ammo in a 24" gives the same damage as period "+P" ammo out of a 30" barrel... I think my stats for Sportified Krags is going to be 7d pi and say the shorter barrel gives the same range stats as the normal powered ammo.  I'm not sure about the ST requirements yet, going to get subjective on that after a trip to the range.

3 comments:

  1. I e-mailed SJG way back in the day and got an 18 on my reaction roll. They sent me complete GURPS 3rd ed. stats for the .30-40 Krag. Would you like me to send them on?

    ReplyDelete
  2. I'll Xerox them and put them in the mail. The e-mail itself was lost long, long ago when I had to drop my Cleveland.freenet.edu account.

    ReplyDelete

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