Young Freud wrote:

For example, a 6.8mm assault rifle (what I'm considering the standard-issue here for EP), being fired by a 115kg morph (technically 80kg morph with 25kg of equipment and protection) would generate a rearward velocity of 6m/s for each round fired

You're technically right, but your math is way off. You're looking at more like 1 m/s for every 20 bullets. v(morph) = v(bullet) * m(bullet) / m(morph) = 7.5g * 800 m/s / 115 kg = 0.052 m/s Basically, if you empty your AR's 30 round clip in the same direction, you're going to be moving at 1.5 m/s, about walking speed, in the opposite direction. Definitely something that could get you in trouble under the wrong circumstances.

Decivre wrote:

Far more of a round's space is taken up by propellant than by the actual bullet.

Space isn't important, mass is. Check out a load table for example: http://www.reloadammo.com/308load.htm Most loads, gunpowder weight is 20-25% of the bullet weight.

Young Freud wrote:

I don't think you're seeing what me and Smokescreen seeing. It doesn't matter what mechanism is being used or what angle the recoil is being transfered or if some recoil goes to their arm and the other goes into their shoulder, it still being transfered into the shooter. And since the shooter's inertia isn't increased by 9.81 times due to earth's gravity, the recoil of a firearm can overcome that shooter's inertia and cause a change in velocity. The only recoil compensation we see that can escapes from the loop of action-reaction that occurs in the firearm that eventually transfers into the shooter is gas venting and counter-mass, like that seen in recoilless rifles.

I see that perfectly fine. What you're not seeing is the feasibility in throwing counter-force in the opposite direction. If the force and mass on both sides equate, the result is a zero-sum in changed momentum. The only problem with current gas-based weapon systems is that they may not eject the necessary mass... which could be compensated for by increasing the amount of gas present.

Young Freud wrote:

You mean like a shell casing, right? Actually, cased firearms still have tons of advantages, especially in space. Outside of being used as counter-mass, the casing can also help by dumping excess heat. Cases do typically weigh more than the bullet, especially with rifles.

Exactly like a shell casing. The issue would be that the casing would likely need to be significantly heavier than the projectile, so it can be flung at a lower speed and still provide equivalent momentum. Otherwise you have a gun firing in two directions, which can pose large problems, friendly fire being the obvious concern.

Smokeskin wrote:

You're using a conservation law here that I've never heard of. Care to explain it to me? The two relevant ones I can see are conservation of momentum (mass times velocity) and energy. And energy I don't really like, for one the kinetic energy contains a square, secondly then there's not necessarily conservation of kinetic energy.

Conservation of momentum. Force is any influence that causes a free body to undergo acceleration, and is a staple term for physics.

Decivre wrote:

Gas-operated shotguns aren't "zero-summed" in this context. Look at conservation of momentum - you NEED mass moving in the opposite direction to counter the projectile. There is NO way around this.

Last time I checked, gas has mass. The only necessity is extruding it out the backend of the weapon.

Smokeskin wrote:

Ok, then you got the formula for momentum wrong, it is mass times velocity, not mass times force.

True. Force directly translates into momentum, not velocity. In that case, an equal amount of force on both sides is largely all that matters, because it will already throw a lighter object with greater speed (and therefore produce similar momentum).

Smokeskin wrote:

Yes, that's how it works, the problem is that gas-operated shotguns don't do that.

No shit. That was exactly what I said. Obviously something needs to be modified from what we use on Earth, doesn't it?

Smokeskin wrote:

I don't see any solution to this involving the expanding gases. There's not enough mass there to do the trick, even if they had advanced shutter valves and such - and if you did vent it back, you'd pretty much get it in the face.

Doubtful. Currently the majority of the weight of a bullet is contained in the casing, rather than the actual bullet. Caseless ammunition would leave the weight fairly well distributed between the bullet, powder and primer. Even if the bullet continued to weigh too much to create a counterforce, an increase in the density of the propellant should suffice. As for getting it vented into your face, this would only apply if such weapons were shaped exactly as they are now. Chances are that kinetic weapons designed for zero-g combat would be designed for such a function, like having a release nozzle made of smart materials or memory alloys which can bend and flex to wrap around the shoulder and vent past the shooter's back.

Smokeskin wrote:

I'd rule that a thruster pack could be programmed to fire to counter recoil. Otherwise, you need to be braced, have your feet in loops or wearing gravity shoes, or you're going to drift if you start shooting with kinetic weapons. Given that 30 rifle bullets gets you up to about walking speed, it should be managable in most circumstances, but something that could catch the unwary.

I agree. Moreover, a mildly trained user or someone who as at least seen videos showing them the effects of recoil in space should probably know about it's effects on momentum. Information is much better distributed in the Eclipse Phase universe. The largest majority will know the need to brace or have a counterforce.

Smokeskin wrote:

Now, railguns. These things fire at 2-3 times higher velocity. I'd say that the slugs in them were also smaller, otherwise the damage ranges wouldn't make sense, and that could balance it out. But they have the same ammo capacity as chemical firearms, and they're not even carrying propellant - but I'd say this was a balance choice or an oversight.

Probably not. While artillery railguns likely throw projectiles in excess of mach 12, info on page 336 only specifies the projectile speed of man-portable railgun weapons at around mach 6+. That's not significantly faster than the current record holders (the .22 Swift and the .223 Winchester Super Short Magnum, both clocked at about mach 3½). However, I think it fair to note that at very high velocities, the amount of damage caused does not increase at equal amounts to speed increase. This is because the speed of the airflow around the round does not increase at the same rate. This is why a sonic boom from things travelling at significantly different speeds do not occur at significant differences in decibel volume (the largest factor for how loud a sonic boom will be is distance, not speed). Hence, the actual tearing force of a bullet as it passes through a target does not equally increase to speed either (because ballistic damage is caused both by the pushing effect of the round, and the vacuum effect as it passes through). The only way that they would be able to cause significantly more damage would be if the railgun round were to hit something that actually stopped the round... which would mean it absorbed the entirety of its momentum and took the full brunt of its effects. This is probably not a commonality, and railguns are more heavily prided for their remarkable piercing quality and potent range. *: [sup]I'm using "mach" in terms of the speed of sound at sea level. I already know that mach changes as altitude and atmospheric density changes. Mach at sea level is generally considered a constant, and is often used in measuring bullet speed.[/sup]

Smokeskin wrote:

So current fastest bullets are around 3.5 mach, with 2.5 being common, and EP states railguns fire at 6+ - that looks like 2-3 times faster... Anyway, most bullets are designed to either deform or fragment, because otherwise they have very poor stopping power. If the bullet is fired at mach 6, there'd be much more impressive fragmentation, with fragments travelling further in the body, and the round would probably be designed around it. There are also other factors, like tearing of the tissue from the temporal cavity created and hydrostatic shock, which would cause greater damage for a faster round. Bottom line is, all else being equal, a bullet going 2-3 times as fast would do much more damage.

Last time I checked, 6 divided by 3.5 was below 2. Correct me if I'm wrong though. Continuing on, railgun rounds are probably not designed for fragmentation. Unlike conventional ballistics, railgun ammunition must be capable of handling extremely high tolerances of friction. Standard rounds at that speed would shatter in mid-flight. Moreover, because of their extremely high ballistic impact, they are more likely to cut clean through all but the most heavily armored targets. You would need to produce a weapon that resist the high heat tolerances caused by atmospheric travel, yet is fragile enough to break upon impact with a harder body... which is a hard juggling game. Even assuming that we did find a way to produce a round that could fragment, these bullet shards would still be traveling at such massive velocities that they would pass right through the other side of soft targets (which are what fragmenting bullets are best used against). Instead, railguns devastate by means of impacting a target with the shockwave caused by the bullet's flight path, combined with the extreme heat of the round caused by friction with the atmosphere as it passes through. That said, they do a decent amount of damage, essentially equivalent to an explosive round of equal size (compare the reactive rounds of normal kinetic weapons). Larger railguns are likely far more potent. Granted, it's a shame that there weren't specialized rounds for railguns. One specific round I think would be of interest would be thermite rounds, which could ignite during travel and devastate a target with even more severe thermal damage. If the friction didn't suffice, then an electrical charge could be passed over the tip of the barrel to ignite the round as it escapes to the open air. Either way the result would be a very potent weapon (albeit range might take a hit, since you are flinging a small blob of molten fluid). Plus, I think that the damage of railguns likely does need to come up (as does the damage for reactive rounds... and just about everything for that matter; damage numbers are very low in Eclipse Phase combat).

Smokeskin wrote:

You seem willfully dense. I'll try spelling it out for you. 6+ means minimum 6 - perhaps what the rail pistols fire. You then take some world record for fast rifle bullets, mach 3.5. Ok, that gets you below factor 2, for the most extreme cases you can find. In reality, mach 2.5 is common. You'd be pressed to find a single bullet except for specialized sniper rounds like .338 lapua and .406 chey tac that breaks mach 3, and even then it is only the lightest bullets for those calibers, and they only just break mach 3.

Bullet speeds will be significantly higher in the vacuum and low-atmosphere scenarios which will be prevalent in the Eclipse Phase setting, simply because they do not have as much atmosphere to interact with. Not to mention that simple progress in the way of propellant and bullet design will likely increase round speeds.

Smokeskin wrote:

Oh please, no more fairyland physics. Neither the shockwave nor the heat is going to be anything but totally insignificant. Look at it this way. Say we fire a 7.5 g bullet at mach 6, that's about 31,212J of kinetic energy at the muzzle. Then we assume at 1,500 m it is only at mach 3, that's 7,803J of kinetic energy. A total loss of 23,409J. Divide that by 1,500m, that's 15J of kinetic energy lost per meter. My body generates 6 times that amount of heat per second. Simple conservation of energy tells us that there's just not enough energy lost to damage anything from its passage through the atmosphere. Don't buy the railgun myths. Railguns have no magical properties, they don't drag hurricanes of plasma behind them or anything. They're just fast moving projectiles. Heck, some current APFSDS anti-tank rounds travel at nearly mach 6, and even a 1,000 times the weight you don't see anything like that happening.

Your body generates 6 times that much heat and spreads it over an object thousands of times the size of a bullet. It's a crappy comparison. The same amount of heat energy condensed into a smaller object is going to be a higher recorded temperature. That's elementary physics. As for the wave of force, [url=http://www.youtube.com/watch?v=emP5D9Klssg]it's something we can already perceive with regular ammunition traveling at slower speeds[/url], and is the primary reason that hit objects splatter so greatly. The effect will be greater with greater velocities, and more so exacerbated in a vacuum environment.