The rifle is the mainstay combat smallarm, given to every trooper. The current situation in the USA and the rest of the NATO countries have the primary projectile being the 5.56x45mm cartridge in various forms, and the “rest of the world” usually either uses the heavier and slower 7.62x39mm cartridge from the AK-47, or the small-caliber upgrade that is the 5.45x39mm from the AK-74. All of these more or less eke about about 5d: The 5.56x45mm M193 cartridge (the 55-grain/3.5 gram version) basically defines what 5d is in GURPS (and also happens to be about right – that bullet/rifle combo – the 55gr projectile at about 1000m/s from a 20″ barrel – punches through about 1/4″ of mild steel). The AK-47 is given 5d+1 in High-Tech, and the AK-74 a “downgrade” to 4d+2.
My own calculations are slightly different here, but only slightly. The 7N6M 5.45x39mm is a 53gr projectile at 880m/s, for 16.8 points of damage: 5d-1 is probably the best fit here; the penetration of 6mm of armor plate at 300m that is claimed (and the Rockwell C core hardended to Rc 60) might speak to a 1.5 armor divisor if such were still used. The AK47 bullet comes in at 19 points of damage, or 5d+1, as listed, at 122gr and 722m/s. My M193 comes in hot based on energy and diameter – it should penetrate for 19.3 points of damage, but empirically does not do so; some quick calculations show that the bullet is probably operating at close to it’s maximum coherence energy, so much kinetic energy in the projectile that the bullet itself can’t take the impact. Either that or (which is more likely) my formula is off by a bit. Either way, all of these come in at roughly 5d.
All that being said, what is enough injury? 3d injury is enough to take a regular Joe with 10HP and have them risking a KO; 6d is a death check. If your foes are human – and that’s the default assumption here – anything more than that is for two things: hitting at range, because you need to reach out and touch someone there, or punching through armor.
For the second, in GURPS, the best way to get armor defeat into the design is by bullet construction, that is to say, armor divisors to knock the protection down, followed by enough kinetic energy to defeat the remaining DR and the threat. For range, again, bullet construction is key, as high aspect ratio projectiles will hold their velocity (and thus damage) better. Retaining full ballistic performance (in terms of the GURPS 1/2D metric) to somewhere between 300 to 500m seems to fit the bill for the man-portable battlefield weapon category, and that’s basically the sweet spot for the 5.5mm type weapons, and the 7.62x39mm also fall in that range – my calculations put all three in the 400yds 1/2D range. That’s because of the relatively low sectional density of the 5.45mm round, and the high cross section of the 7.62mm one.
Battlefield Personal Weapon: Goals
So, the goals here for evaluating the old designs, and developing new ones, will be to improve on the 1/2D range (which also means that velocity loss by using shorter barrels will be somewhat mitigated) into the realm of the older battle rifle range (500-700yds), provide for a (2) armor divisor through bullet design (which will almost certainly mandate some sort of high-density core), and deliver 3d-6d injury after penetrating body armor.
The question of how much armor seems a legit one: modern trauma plates with a woven fiber armor backing will frequently provide about 10d worth of protection – DR 35 – from the plates alone, backed by the woven armor. The typical threat that this is gauged against seems to be the .30-06 M2 AP bullet, which hits for about that penetration.
So any design that’s notionally TL9 should probably stand up well against that level of ballistic threat.
Special Applications Rifles: Goals
The other set of weapons that will exist are what one might call rifles for special applications. Sniping, anti-materiel usage, and payload weapons all fit the bill here. These will put a premium on accuracy, as their usually hefty ammo does not lend well to carrying a lot of it. It will also be a place where versatility will come into play, as the projectiles start to get large enough that explosive, homing, and other special devices become practical and perform well.
Let’s Get To It
That’s a lot of pre-amble: let’s see how the rifles in the book do.
Ultra-Tech Standard Rifles
The book as written provides seven rifle-class weapons. All are assumed to be caseless, and they come in a few flavors. There’s a 5.7mm weapon that fires the same projectile as the PDW discussed in the prior write-up. There are two 7mm designs, two 10mm, a 15mm anti-materiel rifle, and a 25mm payload rifle. Let’s break ’em down. Continue reading “Sunday is GunDay: GURPS Ultra-Tech Rifles”