I posted my prior article on firearms for D&D over on reddit, and a poster noted that while he thought this was all neat and stuff, he was much more likely to be interested in naval cannon.

That seems like a great idea, and I found a nice article online to base some initial stats from: Smooth Bore Cannon Ballistics.

The key data from that is the cross-section of cannon shot from 6-lbs to 32-lbs, which obviously includes shot weight, and also velocity. From that, it’s easy to convert to Kinetic Energy and Mass, which means a D&D damage conversion is somewhat trivial.

An a priori note – these are big, heavy projectiles. The critical range is going to be very large. If you get hit with one of these, it’s going to suck.

The Inputs

The primary inputs can be found in the article above. Taking those and just presenting the results, one gets the following table:

Shot Weight (lbs) Velocity (m/s) Dice Crit Range
1860 [3] 6 438 5d6+1 15-20
12 453 5d6+3 15-20
1862 [5] 18 524 6d6-1 15-20
24 524 6d6-1 14-20
32 381 6d6-2 14-20
32 442 6d6-1 14-20
32 518 6d6 14-20


Parting Shot

The table suggests that small cannon such as the 6-lbr will be in the 5d6 range, while cannon that tended to be used on other ships (12-32lb shot) cluster more or less around 6d6. The expanded crit range should take care of getting solidly thwacked by a 6″ steel projectile.
Note that this is based on a system that gave a .50 BMG 2d12, so it’s necessarily flat.
Overall, though, I don’t think it’s crazy-time. If you’re looking at a 6d6 or 8d6 fireball or lightning bolt, the cannon will straddle that well.
Also, the question arises, I’m sure, why the damages aren’t that far away from each other. Wouldn’t more differentiation be better? Well, again: flat scale. But even in GURPS, with the sqrt(KE) damage scale, relying on KE alone provides “only” a factor of 3 in scaling, and larger balls will tend to have slightly lower penetration (energy dispersed over a wider area), so a spread of 2x from the 6-lb to the most energetic 32-lb is all that’s going to be in it.
For simplicity, I might list three ranged of cannon. Small cannon are 5d6 or 3d10 with a crit range of 15-20; medium cannon are 4d8 with a crit range of 15-20, and large cannon are 6d6 with a crit range of 14-20.

Just for fun, I used the Damage = 4 * Log5(Kinetic Energy) conversion on a longer list of cartridges than I provided here.

As you can see, most weapons fit into a fairly small range of stats. The .22LR does about as much damage as a shortbow (between 1d6+3 and 1d6+4), where a 7.62 Battle Rifle is about 2d10, which converts to 1d10+5 or 1d10+6 – about as damaging as a longsword held in both hands by a ST 20 fighter.

I like using multiple dice because they both roll if you crit, which gives a lot of room for very serious wounds.

That’s the other thing that could potentially be done here, as well, using the principles from expanding the crit range for different armor types. Larger and more damaging projectiles could (should?) have a wider range where a hit is also a crit. I based this entirely off of the mass of the bullet, using a logarithmic scale. My first attempt gave 5/4 * log (Mass) for the width of the range (a .22LR was 2), which gave 19-20 for the anemic .22, and 17-20 for the mighty .50BMG. A 25% chance of a critical hit is pretty great, so I stopped there, though obviously it could be tweaked even more.


One late-breaking idea on the critical range: some of these cartridges/loads should potentially be able to rock the world of nearly anyone. I’ll suggest that for weapons with an inherently expanded crit range like above, that one divides it into segments, with each segment doing more damage.
So instead of a crit is roll the dice twice (2d8 becomes 4d8), you might say that if the crit range is 17-20 or better (so 12-20 to 17-20), then half the range gives double damage, while the other half gives triple or even quadruple.
So a .50BMG does 2d12 on a hit, 4d12 on a 17-18, and 8d12 on a 19-20. (Alternately, reserve quadruple damage for a natural 20). That would make the maximum damage from a 16″ Naval Gun 16d12, max damage 192 points, which can and should threaten just about anyone.

The Reloading Press is an at-least-weekly feature here on Gaming Ballistic for 2016. Each week it looks at some interesting real-world cartridges and presents them with hopefully-useful information in GURPS Format.

9x19mm Parabellum

The 9x19mm was invented by Luger in 1902. It is perhaps the most widely used pistol cartridge worldwide, and with recent advances in hollow-point ammunition reliability, is poised to reclaim its former spot as the issue cartridge of the FBI over the .40S&W.

There are many loads for the pistol, but the most common seem to be the 115gr, 124gr, and 147gr loads. They are usually available in full metal jacket (FMJ) and various flavors of hollow point. From a GURPS perspective, the most important load is probably the 124gr NATO standard round – an 8 gram bullet fired at 1250 fps from a 5″ barrel – it’s the standard for 2d+2 as well as pi pistol rounds. A reference bullet, so to speak, defined as doing both 9 points of penetration and 9 points of injury.

So we’ll work that one up, and then talk about variations.

Ballistic’s Calculator Inputs

Basic inputs for the calculator are as follows, selecting 127mm for the (test) barrel length.

  124gr 9x19mm  
Chamber Pressure 32900 psi
Barrel bore 9 mm
Case Length 19 mm
Chamber Bore 9 mm
Barrel length 127 mm
Bullet Mass 124 grains
Aspect Ratio 1.85 L/Bore
Burn length 8 mm
Projectile Caliber 9 mm
Total Accelerated Mass 124 grains
Expansion Ratio 1.66 expansion
Projectile Load 1
Output Stats

The pistol cartridge is relatively high power as far as pistols are concerned – much more so than the .45 ACP that it was supposed to replace (and from a service perspective, largely did replace). It develops a considerable velocity in a short barrel, and the lowest penetration predicted by the model is on the order of 2d out of just over a 1.5″ barrel – not that anyone uses one that short. Even derringers come with a 2.5″ barrel, mostly!
So, here’s the chart:

  • The velocity is at the muzzle. The velocity with a 5″ test barrel is tuned to match real-world data at 1250fps, for NATO standard ammo. This is not the highest energy 9mm available, but it is the standard GURPS 2d+2 pi bullet, so it’s what I chose. 
  • 1250 fps is pretty good for a 9mm load, though – not that you can’t get more, but in self-defense loads (JHP), the fastest 124gr tested at this site was slower than the standard FMJ NATO load.
  • There is no pi to pi- range; this bullet does not gain appreciable wounding by tumbling.
Some more notes on barrel length. You can see that it will penetrate as well as a .45 ACP with derringer-length barrels. At the more standard 2.5″ or higher, it’s at least 2d+1, and in the “service pistol” barrel length from 4″ to 5″, it’s all 2d+2.

Now, for SMGs you can get longer barrels – but not as long as you might think. The MP5K has only a 4.5″ barrel (2d+2) but can hold a lot of bullets and fires them quickly. The more robust MP5 is 225mm for the longest barrel, which only ekes out 3d-1. To get to the full 3d you’ll need/want a 9.5″ barrel, but you can’t get to 3d+1 until you’re over 450mm. Even the Beretta Cx4 Storm is only 422mm – most carbines seem to like to come in 16″ barrels or smaller (3d), but the Citadel M1 does come with an 18″ barrel that should deliver about 3d+1. Of course, if you are toting a 35″ weapon around, you can do a lot better than that for damage, ammo weight, etc with a 5.56x45mm carbine or even a full-size rifle in a bullpup. The reason you do this (carbine in 9mm) is for Accuracy, not damage.

Alternate Loads

As noted earlier, the more common loads than the military one will be hollow points. That being said, there are slightly hotter 124gr FMJ loads, the hottest I could find only being 1310fps, which my model gives as being achieved at about 36,200psi input. That gives 9.8 points of damage, which is enough to eke out 3d-1 pi.

Alternate loads tend to be alternate weights, with a lot of 115gr stuff being available as very high velocity rounds, especially from SMGs, and 147gr heavy bullets from pistols, both of which are available in JHP. The heavier bullets will tend subsonic, which makes them excellent for platforms like the MP5SD6 – an integrally suppressed weapon.

Some of the best JHP will expand to as much as 0.6 to 0.7″ in diameter, which is roughly double what the starting diameter is. That’s very good, and more typical of JSP rifle rounds – which have a lot more body to work with.

That means a proper JHP round really earns it’s pi+ rating. The GURPS rules give JHP ammo a (0.5) armor divisor. The more accurate way to do it is to subtract 1 point of penetration per die. Lo and behold, this makes the best 9mm hollow point from the prior web page (1170fps and 0.66″ expansion, the Golden Saber +P loads) provide 2d pi+, which is the same penetration and injury as a .45 ACP, but with a heck of a lot more shots per magazine and less recoil. 


There are almost too many to count. I’ll ping in a few important ones.

Pocket pistols with a 2.5″ barrel that would include derringers and small concelable pistols like the Kahr and other 9mm models. These will often hold fewer than 10 rounds.

Concealed carry pistols with a 3-3.5″ barrel that are “commander-sized,” which means small and easy to carry, but likely double-stack weapons that will hold over a dozen shots, perhaps closer to 15.

Full-sized service pistols with 4-5″ barrels. These will hold 15-18 shots in the magazine.

SMGs and Carbines with 9″ to as high as 16″ barrels. Nearly all will do about 3d-1 or 3d pi damage, and with the right hollow-point round will deliver 2d+2 pi+, which is a good reason to carry one (still not as good a reason as to carry a carbine with an assault rifle chambering for many reasons).

As noted above, subsonic 9mm is good for suppressed weapons, the most famous of which is probably the MP5SD series.

The Reloading Press is an at-least-weekly feature here on Gaming Ballistic for 2016. Each week it looks at some interesting real-world cartridges and presents them with hopefully-useful information in GURPS Format.

6.8x43mm SPC

The 6.8x43mm SPC cartridge was introduced as an attempt to increase the lethality of the M16 and (especially) M4 pattern rifles. The cartridge is more-or-less designed to fit into the same magazine length as the 5.56x45mm NATO standard bullet (but it’s not true that they use the same magazines – they don’t), and the lower receiver of the AR15/M4/M16 platform can be used unmodified with the new cartridge. The bolt, chamber, and barrel of course must change, and that can be done with an upper receiver swapout.

Whether or not this was the true design goal, one outcome of the design process that led to the 6.8x43mm is that the test velocity of the barrel is achieved with a 16″ barrel, rather than the 20″ standard for the 5.56x45mm. That means that the M4, with its 14.5″ standard barrel, is much closer in barrel length to the optimal barrel the cartridge is designed around.

Ballistic’s Calculator Inputs

Basic inputs for the calculator are as follows, selecting 406mm for the (test) barrel length.

6.8x43mm SPC
Chamber Pressure 54000 psi
Barrel bore 6.8 mm
Case Length 43 mm
Chamber Bore 10.7 mm
Barrel length 406 mm
Bullet Mass 115 grains
Aspect Ratio 3.6 L/Bore
Burn length 21.3 mm
Projectile Caliber 6.8 mm
Total Accelerated Mass 115 grains
Expansion Ratio 2 expansion
Projectile Load 1

Output Stats

The rifle develops appreciable damage at near pistol-length barrels, at least within the assumptions of the calculator. It would equal the injury of a .45 ACP even at pi- ratings in a barrel the size of a long revolver. Even so, calling it “pi-” does it little justice. It would earn a wound channel modifier of 0.7 if the scale were left open to any number, compared to the 0.5 of the 5.56x45mm, the 1.0 of a 9mm, and a 1.2 of a 0.40 S&W.
So, here’s the chart:
  • The velocity is at the muzzle. The velocity with a 16″ test barrel is tuned to match real-world data at 2575 fps, the highest energy load listed on the Wiki page. I do this because GURPS damage is based on kinetic energy, so no GURPS PC worth their salt will choose anything less than the highest energy if pure penetration/lethality is at issue. If you’re doing supppressed subsonic shooting, that changes.
  • The pi to pi- range is where the damage drops from piercing to small piercing. For very short barrels (smaller than 177mm in my model), the bullet is slow enough that it will not yaw and fragment, and so it’s only good for pi- rather than pi. This is defined as 600m/s in my model, which is somewhat arbitrary.
  • It’s possible that the damage (penetration, really) is perhaps 10% high. That would still give a 20″ barrel about 6d-1, and a 14.5″ barrel 18 points of penetration, or a full 5d out of an M4 platform.
At any useful barrel length for a rifle cartridge, that is, about 9″ and higher (and that’s a darn short rifle), there is some appreciable range at which it will do its full pi damage type. It is an intermediate between the 5.56 and 7.62 NATO offererings in almost every way:
  • Half the diameter of the two rounds would be 6.59mm
  • Half the bullet weight between the 62gr and 168gr standard marksman’s bullets for each platform is 115grains, which is where the standard bullet comes in
  • The standard AR-15 length magazine holds 25 rounds of 6.8mm SPC; the AR platform magazines typically hold 30, while the 7.62×51 hold 20.
  • The 7.62 is about 3400 Joules, the 5.56 about 1760J. Average that to get about 2,550J, where the actual round comes in at about 2,300J.
For GURPS gunners, it’s a very good cartridge. 6d out of a 16.5″ barrel makes for a one-shot death check against Joe Average, bringing him from 10 HP to -11 HP in one torso hit. Against the vitals, 21 turns into 63, enough for a one-shot instant auto-kill. Highly efficient. The Rcl for these weapons is typically 2, so it’s no worse than the M4 or M16 it replaces, and better than the full-size battle rifles. The 1/2D range of 530yds is 30% higher than the 5.56x45mm.
Regardless of the real-world, it’s a fine, fine cartridge in GURPS.
Not everyone feels the same way about the cartridge in the real world as it stacks up vs. the modern versions of the 5.56x45mm, the Mk262 77gr long-range cartridge. A data-intensive comparison can be found here.

You need a purpose-built upper receiver (or at least a barrel, chamber, and bolt change) to shoot this cartridge. Some rifles and uppers can be found below.

  • The Barrett REC7 is the only 6.8 SPC rifle statted up for GURPS, found (of course) in GURPS Tactical Shooting. For a list price of $2,800, one can be yours.
  • I would love to get my hands on a Desert Tech MDR in 6.8 SPC, but they’re not out yet. They’re also supposed to cost between $2,000 and $3,000. But it’s a bullpup, so mrowr.
  • Stag arms makes a piston-driven platform in 6.8x43SPC that’ll run the buyer about $1,100, but you need to have a lower receiver to put it on (about $300, and that’s the part that counts as a “firearm.”
  • LWRCI went the entire nine yards, redesigning the magazine well and contractiing with Magpul to make the only polymer-case magazines for this cartridge. The rifle itself is about $2,200 complete, and each magazine costs a darn-reasonable $25.
  • The magazines for these rifles are quite finicky in my experience. Of the four 25-round steel magazines I own, two will not feed reliably. Barrett and Magpul make good ones, for $50 and $25, respectively.
  • You can find some of the above, and many others, in this article. They’re all probably very expensive, though – this round never caught on as much as marketing hoped it would!

The Reloading Press is going to be a new short feature for me in 2016, based on a few comments from friends of mine in other media.

Each post will contain a cartridge and stats for GURPS – sort of. The way I’ll be doing this is to use my ballistics calculator, which will give gameable and consistent stats.

In many cases, there won’t be much difference between various versions of a bullet or cartridge. As an example, at some point I’ll compare 115gr ,124gr, and 147gr 9mm ammunition. That will, within GURPS’ resolution, likely not amount to much.

5.56x45mm Mk318 mod 0

This cartridge is the USMCs answer to the fact that the 62gr M855 (about 4 grams, and 940m/s out of a 20″ barrel) didn’t pereform that well when fired out of the usual short-barreled M4 carbine, which has a 14.5″ (370mm) barrel standard.

The ammo is built to a 2 MoA standard, which means that the maximum accuracy a weapon can get using this ammo is Acc 5 (about 1.8 MoA, close enough).

Pertinent stats for the ballistic calculator:
Continue reading “Reloading Press: 5.56x45mm Mk318 mod 0”