Concept: Amphibious AC ammunition

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AmaroqStarwind
10/18/21 12:54 PM
172.58.101.10

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Using more advanced sealing techniques, monopropellant chemistry, and hydrophobic plasticizers and projectile coatings... underwater ammunition could be developed that would not only function fine when fired at depth (thanks, monopropellants), but also perform adequately when fired into water from above (thanks, hydrophobic projectile coating).

The three major downsides could include:
- Increased risk of an ammo explosion (monopropellants don't need separate oxygen supplies to burn), meaning that high heat levels are more likely to cause a detonation, and you can still suffer an ammo explosion underwater (if there are any rules that prevent that from happening)
- The inability to use other ammunition types (they aren't designed for amphibious use and don't have the same sealing) without being completely out of the water for a full turn in advance
- Increased ability for sonar-based targeting to accurately track you while you're firing (due to the cavitation around the hydrophobic bullets)

Another, much less apparent downside would of course be cost.
I wouldn't suggest ammo per ton as a downside, because honestly there's no physical explanation I can realistically pull out of my hat to explain why, plus these specialty bullets would not provide any on-land benefits. Adding a weight penalty would kinda just be beating a dead horse.
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ghostrider
10/18/21 05:32 PM
45.51.181.83

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Underwater explosions from heat is a bit messy. Vehicles have special features about them when it comes to ballistic and missile weapons that they can't overheat. This makes overheating something that can not happen with the rule set. Mechs can overheat and have the slow movement, shut downs, and heat explosions.
Only energy weapons produce heat, and vehicles must have enough sinks to dissipate it, or it won't be able to fire the energy weapons.
The last rule set that I have seen have vehicles being destroyed on a roll of 7+ when entering a hex on fire, or being hit with infernos. Not sure if you can heat up water normally to do something like this.
So a house rule will need to be done, or vehicles won't suffer a heat explosion.

I would suggest that any critical hit have a lower target number for an explosion if the ammo is more unstable then normal ammo.
I would need to know a little more about the ammo and it's targeting and tracking abilities before committing to things, but I would suggest if fired above water, there be a heavy penalty, to not being able to fire at all, due to the propellant concept. I would assume something like folding fins to help stabilize the shot, but this is just an assumption.
How many shots per ton, as well as damage would be nice to know. This would give a little more information to determine pricing. Higher tech means more money, and probably lower shots per ton.

One thing to think about is if the ammo is highly explosive, then the question of how it ignites comes to mind. Gauss ammo is kinetic energy, so the speed and power does the damage. Explosives hitting the water might be an issue.
Though a side effect of explosives underwater means water rushing back into the explosion area might do additional damage. Much like what happens with a torpedo hit.
AmaroqStarwind
10/19/21 01:34 PM
172.58.100.98

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I'll first try to answer some of your questions regarding firing into water from above, and firing on land;
- Monopropellants are substances where either the fuel and oxidizer are pre-mixed (sometimes with a catalyst), or the fuel itself already contains an oxidizer in its chemical makeup. As such, it should still be able to fire on land without blowing up... most of the time. (Meaning it might still happen on a Nat 2, but only on land, as operating underwater provides sufficient cooling to prevent this outright.)
- A hydrophobic plasticizer would be able to contain the semi-solid fuel without getting wet.
- A superhydrophobic coating on the projectile will trap a small blanket of air around the projectile, significantly reducing drag as the projectile's wake will form a torpedo shape (even if the projectile is a perfect sphere). This greatly reduces kinetic energy loss.

Regarding your other questions, I'm not sure I have good answers for those yet, but I'll try. I'm scrambling to get some medical stuff taken care of today.

-=-=-=-=-

I do like the idea of critical hits having a much higher chance of causing an ammunition explosion, however...

1. As for the targeting and tracking abilities, it's primarily just an unguided round for a normal autocannon. Even if the projectile had stabilizing fins on it for underwater use, it's not much different from regular autocannon ammo in that regards.
2. And with the whole ammo-per-ton thing, I was trying to avoid that. I'd need to come up with a really good excuse for the extra weight.
3. I completely forgot about vehicles. Oops.
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Edited by AmaroqStarwind (10/19/21 01:51 PM)
ghostrider
10/20/21 12:14 PM
45.51.181.83

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One possible excuse might be the ballistics causes an increase in breeching, or causes the pilot to have a penalty to staying up when hit by it.
Granted, neither one really is a good idea. Torpedo explosions should be greater force, while the breeching idea doesn't really follow normal ballistics.
Well the ammo does have the propellant part of it, so it isn't that far out.

But something I didn't see stated.
Is this for MGs, ACs, or both?
The amount per ton can be a round or two less then the normal AC amount, or maybe the same amount but it is so packed, this causes the increased chance of explosion when hit. Also a chance to jam might be added in, to account for the ammo being so tightly packed.
Then again, it might only come in 1 1/2 ton increments because of the size of the ammo, but I would suggest extra rounds to help compensate for the extra weight.
AmaroqStarwind
10/20/21 10:44 PM
172.56.14.7

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Thread title says AC. I suppose it could also apply to MGs, but I'd never heard of alternate MG munitions before.
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ghostrider
10/20/21 11:31 PM
45.51.181.83

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I know tracer rounds are part of MG ammo, but not sure if it is the same thing as phospherous (spelling?) rounds. Technically, there is armor piercing rounds, which differ some from normal rounds. If I know right, uranium depleted is yet another type of mg round, as I am pretty sure it isn't standard for MGs in real life. I am probably wrong on this.

The game doesn't seem to differentiate from them. I think they use nothing but the hardened armor piercing rounds for everything.
And this is assuming the vehicle/mech MG, not the hand held ones.

For logic issues, the question of if you clear the water from the barrel when firing, or just before the shot is sent out come up, or if the shot isn't affected from hitting the water at high speeds comes up.
Might well have water in the breech so it starts off in the water and doesn't 'impact' it. Such as flooding the torpedo tubes before they fire.

A quirk that might help is the ammo has to be stored in water, or it loses it's potency. The closest thing to this I can think of is the SR-71 having porous fuel tanks that seals up as it heats up moving thru the atmosphere. Could be the propellant ignites in open air...
AmaroqStarwind
11/02/21 06:41 PM
8.20.123.157

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Self-ignition? That's a horrifying thought...
"I've always recommended a good pair of running shoes."
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Qoonpooka
11/04/21 11:00 AM
40.132.250.62

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The thing about underwater ballistics: it's not a lack of oxygenation for the propellant (which is why you can use ACs in vacuum) that's at issue: it's the medium you're trying to shoot through.

The resistance air puts on a bullet is negligible. Water, including the water in the barrel, is a whole different story.

Now, if realism to physics isn't a thing you care about at all then you're doing just fine. But the reason missiles/torpedoes work in water is because they're not concerned with still having enough momentum on-target to inflict damage: they bring the boom as a payload. But a bullet doesn't have a payload that goes boom.

If you want an interesting alternative to the autocannon in the same vein as the torpedo launcher is to missiles then you might go with a purely concussive weapon that consists of an explosive charge that is shaped by the 'barrel' and channels the force of the propellant into a sort of underwater energy weapon. Water conducts sound VERY well, so it'd presumably conduct this force very well. It'd be hilariously short-ranged, but could hit like an AC without needing a physical projectile at all.

Upside: more room for more shots (similar to how caseless AC ammo works).

Downside: bigger ammo booms, I'd probably make the weapon go boom like gauss rifles do if it's loaded when it takes the crit.
AmaroqStarwind
11/05/21 07:23 PM
172.56.15.117

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Again, the projectile would have a pocket of air around it, and would basically become a streamlined torpedo shape. This means that the water would only have as much resistance as air would. See the link in my second post.
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