Gun design: Muzzle energy, bullet caliber, and recoil

[Ulzgoroth]

Originally Posted by BraselC5048

DR 14 to 16 is expected. Doing the math again, it looks like APDS rounds really need to be issued, 4d (2) pi, in order to actually have decent effect past armor. Of course, the Navy's HEAT rounds do much better.

Well that's a compelling case for making your pistol big and heavy.

Originally Posted by BraselC5048

Is that in the edition of Pyramid that isn't available in any way, or a different edition. I'm still dying to see Lockwork for GURPS, but I have no idea if I'll ever see it. My campaign is more or less TL 8^, for the most part, without any great amounts up incredible technology, and I keep the superscience to a bare minimum.

It's the current-series Pyramid. It came out not many months ago and is on w23.

Originally Posted by BraselC5048

One thing I've been wondering, would a gun with Very Reliable and High-Cyclic Controlled Bursts be more likely to jam in a vacuum? It seems to me like very high rates of fire with extremely high precision construction wouldn't do well at all under harsh conditions.

Very Reliable probably doesn't mean extremely narrow tolerances. Precision manufacturing is never bad, but something that has to be together just right to work is delicate, not rugged.

Dunno what effect high-cyclic bursts have on reliability. I think the high-cyclic weapons written up typically have no special reliability problems, so I wouldn't add any.

On the other hand, heat dissipation in vacuum is a serious pain, so any weapon that puts out a high sustained rate of fire is going to need special attention or sparing use.

If your guns are meant for use inside ships that may have had their atmosphere dumped, that might simplify the problems some, too. Open space can be very hot (in strong sunlight) or very cold (...when not) and while equilibration is slow, it will happen. But the personnel spaces of a spaceship with the air dumped is still going to be relatively close to room temperature. You've still got to account for the lack of atmospheric pressure and convective cooling, but less for extremes of temperature.

[Fred Brackin]

Originally Posted by Anthony

In general, if you're willing to use a ranged weapon in the first place, you're not that concerned about damaging things downrange; .

Gasses from the barrel cylinder gap don't go downrange. They go sideways and expanding in a vacuum could go backwards too. They could easily bounce off a nearby bulkhead as well.

In the Mythbusters experiment they went _everywhere_, filling the entire vacuum chamber.

[BraselC5048]

Originally Posted by Ulzgoroth

Well that's a compelling case for making your pistol big and heavy.

It's the current-series Pyramid. It came out not many months ago and is on w23.

Very Reliable probably doesn't mean extremely narrow tolerances. Precision manufacturing is never bad, but something that has to be together just right to work is delicate, not rugged.

Dunno what effect high-cyclic bursts have on reliability. I think the high-cyclic weapons written up typically have no special reliability problems, so I wouldn't add any.

On the other hand, heat dissipation in vacuum is a serious pain, so any weapon that puts out a high sustained rate of fire is going to need special attention or sparing use.

If your guns are meant for use inside ships that may have had their atmosphere dumped, that might simplify the problems some, too. Open space can be very hot (in strong sunlight) or very cold (...when not) and while equilibration is slow, it will happen. But the personnel spaces of a spaceship with the air dumped is still going to be relatively close to room temperature. You've still got to account for the lack of atmospheric pressure and convective cooling, but less for extremes of temperature.

They're ment for use inside ship, but the hull (or at least parts of it) could be up to 150 degrees F after a long battle, since the ship itself is a heat sink for the lasers's waste heat. My current overheating rules halve the number of rounds required from High Tech- any suggestions if it should be more or less?

Originally Posted by Fred Brackin

Gasses from the barrel cylinder gap don't go downrange. They go sideways and expanding in a vacuum could go backwards too. They could easily bounce off a nearby bulkhead as well.

In the Mythbusters experiment they went _everywhere_, filling the entire vacuum chamber.

I doubt they'd do much beyond a few inches, and even then only directly out to the side. There's very little mass there, and the more it spreads out, the less force it has at any spot, or in general. Perhaps the uniform needs to go through the wash, but I doubt much else. Background color, perhaps?

Kind of like hypervelocity shrapnel, actually. Sure, in theory it's a threat, but the hit likely wouldn't accelerate the shrapnel any higher initially then it does in an atmosphere. And it's not the atmospheric slowing is a major effect over a few meters, and there's not exactly a lot of large open spaces. I treat laser hits as doing 6d cut, and missile hits as doing 8d cut. Or unlikely to do more then a flesh wound past body armor.

On the other hand, that boarding action began with the ship getting surprised at point-blank range. Nobody was wearing body armor, and the shrapnel and splinters were nasty. The captain and someone on the bridge were killed by splinters to the neck, possibly partly decapitated, another crewman on the bridge had his leg crippled, the second lieutenant was hit in the arm and taken out of the fight, and a poor crewman on the bridge got a ship's laser to the chest, and was undoubtably hit by multiple splinters as well.

[Phoenix_Dragon]

Originally Posted by Fred Brackin

Gasses from the barrel cylinder gap don't go downrange.

And after traveling a mere foot, the cloud of radially expanding gases from that gap are down to a fraction of a percent of its density (And that's not even counting its own pressure spreading it out further to the front and back). As someone who's had his fingers hit by the kind of expansion you're talking about from a hotloaded .44 revolver when my finger was nearly touching the cylinder (I was a kid), I would not consider that a credible danger to me or anyone else when someone might be shooting actually bullets at me.

Also, he said "handgun," not "revolver."

[lwcamp]

Originally Posted by BraselC5048

Anyway, I've been stating up some fictional guns. The thing is, can you increase the caliber without increasing the muzzle energy (not a big a loss of velocity, since it is squared in the equation, after all)? And keep the recoil of the smaller caliber?

Two specific guns:

A .455 revolver, with the muzzle energy and recoil of a .357 magnum. So 3d damage, recoil 3, although firing a heavier bullet - is that right?

A .455 SMG (the revolver takes it's ammunition, but not vice versa), based on the KP/31 Suomi, much more out of GURPS:WWII then High Tech, with appearance crossed with a Lanchester Mk I. Muzzle energy is the same as a 9mm, 3d-1. Acc 4, despite the lower energy, keeping the Suomi's reputation for accuracy, even if a .455 SMG should get Acc 4 anyway. 1/2d is 200 yards (accuracy again - is there a rule about aiming bonuses past 1/2d in 4e?), as well as the Fine (reliable) that it should have had in High Tech to begin with. Recoil is 2, from having the muzzle energy of a Recoil 2 9mm SMG. Does that all sound about right?

For what it is worth, I have a calculator implementing a model that fits GURPS handgun damage fairly well
http://panoptesv.com/RPGs/Equipment/...s/GunStuff.php

Using this model, for a 17 gram, .455 caliber bullet at 325 m/s (to get a similar muzzle energy to a .357 magnum) from a 1.1 kg pistol I find a damage of 3d Pi+, Min ST 10, Rcl 4.

For a 17 gram, .455 caliber bullet at 217 m/s (to get a similar muzzle energy to a 9 mm parabellum bullet) from a 4.6 kg SMG treated as a longarm I find 2d Pi+ to 2d+1 Pi+, Min ST 9, Rcl 2

Luke

[Green-Neck]

Originally Posted by lwcamp

For what it is worth, I have a calculator implementing a model that fits GURPS handgun damage fairly well
http://panoptesv.com/RPGs/Equipment/...s/GunStuff.php

Using this model, for a 17 gram, .455 caliber bullet at 325 m/s (to get a similar muzzle energy to a .357 magnum) from a 1.1 kg pistol I find a damage of 3d Pi+, Min ST 10, Rcl 4.

For a 17 gram, .455 caliber bullet at 217 m/s (to get a similar muzzle energy to a 9 mm parabellum bullet) from a 4.6 kg SMG treated as a longarm I find 2d Pi+ to 2d+1 Pi+, Min ST 9, Rcl 2

Luke

So... To get the same penetration with a 11mm bullet as a 9mm bullet (at 1.5 times the area) wouldn't you need 1.5 times the energy?

[Fred Brackin]

Originally Posted by Phoenix_Dragon

And after traveling a mere foot, the cloud of radially expanding gases from that gap are down to a fraction of a percent of its density (And that's not even counting its own pressure spreading it out further to the front and back). As someone who's had his fingers hit by the kind of expansion you're talking about from a hotloaded .44 revolver when my finger was nearly touching the cylinder (I was a kid), I would not consider that a credible danger to me or anyone else when someone might be shooting actually bullets at me.

The cloud of gasses is less dense but all particles in it maintain the same (very high)velocity.

Also, your finger did not come into contact directly with the propellant gasses. It was instead air to which the gasses had transferred their energy. Much denser but much lower velocity.

Hot thin plasmas are incredibly poor penetrators of normal atmosphere. They transfer all of their energy in no more than inches. That's why "plasma weapons" have to be superscience.

There are safety precautions that have to be followed about gasses even in atmosphere. No atmosphere means much more stringent precautions.

[Fred Brackin]

Originally Posted by Green-Neck

So... To get the same penetration with a 11mm bullet as a 9mm bullet (at 1.5 times the area) wouldn't you need 1.5 times the energy?

Yes, Gurps bullet penetration is calculated by KE/frontal area. To maintain a certain level of penetration KE must increase at the same rate as surface area.

All other things being equal, mass increases as the cube while surface area increases with the square so you won't need quite as much increase in velocity as the percentage increase in KE might lead you to believe.

[Ulzgoroth]

Originally Posted by Fred Brackin

Yes, Gurps bullet penetration is calculated by KE/frontal area. To maintain a certain level of penetration KE must increase at the same rate as surface area.

Not really, no.

It's closer to KE/cube root of cross-sectional area. (Which is not the same as surface area.)

[lwcamp]

Originally Posted by Green-Neck

So... To get the same penetration with a 11mm bullet as a 9mm bullet (at 1.5 times the area) wouldn't you need 1.5 times the energy?

It depends on how you deliver that energy. If you increase the mass by 1.5 times while keeping the speed the same, then you end up with the same sectional density and penetration doesn't change. If you increase the speed by a factor of sqrt(1.5) while keeping the mass the same, you loose more energy to hydrodynamic drag upon encountering the target so that penetration is lessened.

Luke