Rail Gun Ammo Drums

[Mack]

(Warning - pointless analysis ahead!)

I was perusing CWC and looking at the Skelebots when the rail gun capacity caught my eye. The C-200 drum holds 2,000 rounds but weighs only 100 pounds. 100 pounds is pretty light for an unlimited endurance bot with a PS 30. So I started thinking about maybe the size of the drum was an issue. This silly thought lead me down the path of figuring out how large the ammo drum would be, and then that of other rail guns for comparison.

I'll skip all the math, but I used the density of Tungsten to figure out the size (volume) of each round, multiplied that by the payload, and then doubled it to account for the drum itself (feed mechanism, open space, etc). Here's the result:

Code: Select all

Weapon       Payload    Weight     Drum Diameter  Drum Length

C-40R        3000       190 lbs    8 inches       10.9 inches
(Samas)

C-200        2000       100 lbs    6 inches       10.2 inches
(Skelebot)

NG-202       6000       300 lbs    10 inches      11.1 inches
(Samson)

TX-50        2000       100 lbs    6 inches       10.2 inches
(Triax)

TX-250       3000       250 lbs    8 inches       14.3 inches
(Triax)

TX-500       1170       80 lbs     6 inches       8.2 inches
(Triax)

So the ammo drum for a Skelebot's C-200 would only be around 6 inches in diameter and 10.2 inches long. Plenty small enough to carry a spare drum. (Or even better, dual wield C-200s with two drums.) Most rail guns had similar results.

[Killer Cyborg]

Nice!

[Natasha]

(Warning - pointless analysis ahead!)

I was perusing CWC and looking at the Skelebots when the rail gun capacity caught my eye. The C-200 drum holds 2,000 rounds but weighs only 100 pounds. 100 pounds is pretty light for an unlimited endurance bot with a PS 30. So I started thinking about maybe the size of the drum was an issue. This silly thought lead me down the path of figuring out how large the ammo drum would be, and then that of other rail guns for comparison.

I'll skip all the math, but I used the density of Tungsten to figure out the size (volume) of each round, multiplied that by the payload, and then doubled it to account for the drum itself (feed mechanism, open space, etc). Here's the result:

Code: Select all

Weapon       Payload    Weight     Drum Diameter  Drum Length

C-40R        3000       190 lbs    8 inches       10.9 inches
(Samas)

C-200        2000       100 lbs    6 inches       10.2 inches
(Skelebot)

NG-202       6000       300 lbs    10 inches      11.1 inches
(Samson)

TX-50        2000       100 lbs    6 inches       10.2 inches
(Triax)

TX-250       3000       250 lbs    8 inches       14.3 inches
(Triax)

TX-500       1170       80 lbs     6 inches       8.2 inches
(Triax)

So the ammo drum for a Skelebot's C-200 would only be around 6 inches in diameter and 10.2 inches long. Plenty small enough to carry a spare drum. (Or even better, dual wield C-200s with two drums.) Most rail guns had similar results.

How did you get diameter and length knowing only the volume?

[Mack]

It's arbitrary. I just assumed an ammo "drum" would have the proportions of a typical cylinder (not too skinny or too fat) and fit it to the volume accordingly. The main thing is that it gave me an easy reference to visualize.

It's meant to be a good enough answer for a gaming table. Nothing more.

[Natasha]

It's arbitrary. I just assumed an ammo "drum" would have the proportions of a typical cylinder (not too skinny or too fat) and fit it to the volume accordingly. The main thing is that it gave me an easy reference to visualize.

It's meant to be a good enough answer for a gaming table. Nothing more.

I reckoned so, but I just wanted to be sure.

Although at first blush, there seem to be some square-cube law issues. But more pointless analysis would be required to say for sure.

[Mlp7029]

CWC page 121 has a rear view of the Striker SAMAS and shows the rail gun ammo drum. Your sizes seem reasonable compare to that image.

[glitterboy2098]

using this, roughly how much volume would there be per round? that would give us an upper limit on how big the individual slugs are.

[taalismn]

I love you. I was just trying to figure out a few new light vehicle designs based around rail guns.

[Mack]

using this, roughly how much volume would there be per round? that would give us an upper limit on how big the individual slugs are.

Code: Select all

Weapon       Round Volume (in3)    Rd Diameter   Rd Length
             (Cubic Inches)        (Inches)      (Inches)

C-40R        0.091224              0.4           0.719
(Samas)

C-200        0.072019              0.4           0.568
(Skelebot)

NG-202       0.072019              0.4           0.568
(Samson)

TX-50        0.072019              0.4           0.568
(Triax)

TX-250       0.120031              0.4           0.956
(Triax)

TX-500       0.098487              0.4           0.784

I arbitrarily set all the diameters to 0.4 inches (or 40 caliber) and then solved for the length. Notice that three of them are exactly the same size, while the TX-250 uses a considerably larger round.

[Mack]

CWC page 121 has a rear view of the Striker SAMAS and shows the rail gun ammo drum. Your sizes seem reasonable compare to that image.

Whohoo! Dumb luck counts!

I seriously doubt the authors & artists calculated the volumes like I estimated. I consider it a happy happenstance that my figures are close to the drawing.

[Shark_Force]

aww, i was hoping for the repeat of the refrigerator-sized ammo drum on the back of the glitter boy

[glitterboy2098]

aww, i was hoping for the repeat of the refrigerator-sized ammo drum on the back of the glitter boy

well it helps that no one is going around adding an extra zero to standard railgun drum capacities.

though i've occasionally kicked myself for not adding a blue police callbox to this pic

[Shark_Force]

aww, i was hoping for the repeat of the refrigerator-sized ammo drum on the back of the glitter boy

well it helps that no one is going around adding an extra zero to standard railgun drum capacities.

though i've occasionally kicked myself for not adding a blue police callbox to this pic

from the sound of things, even an extra zero wouldn't be nearly as absurd of an image... a bit of time with a calculator suggests 2.15 as a reasonable approximation for the cube root of 10, so multiplying all listed dimensions by that should get you the extra zero i think. so a SAMAS, for example, would have an ammo drum 17.2 inches in diameter, and 23.435 inches long (give or take). that's fairly large, but i don't think it would be humorously large...

[glitterboy2098]

yeah it is the soda can size of the boomgun rounds that make the GB's current ammo load absurd.

[ShadowLogan]

I'll skip all the math, but I used the density of Tungsten to figure out the size (volume) of each round, multiplied that by the payload, and then doubled it to account for the drum itself (feed mechanism, open space, etc). Here's the result:

A few questions:
1. Why Tungsten? IIRC isn't it supposed to be steel/iron? (though it might not even be identified AFAIK in Rifts, one of the Japanese RG's mentions using a lighter material for the round, then there is a Railgun in Robotech 2E that uses Tungsten, and what happens if you use more common material iron/steel for damage output).
2. Not to throw a monkey wrench into your work, but how does altering the shape of the projectile to the stated "metal spikes, balls, or rings" (RMB pg225 or RUE pg270 Railgun description) impact the results since we aren't told normally what the shape of the slug is in a given RG (AFAIK only the Boomgun-type has that specific distinction).

[Natasha]

The shape could dramatically alter the results. Since the choice is arbitrary, trial and error could perhaps find one that yields similar results across shapes. But those results could be absurd; for example, the radius is cubic in the volume of a sphere but quadratic in cylinders.

Adding a zero to the payload is a problem. For the SAMAS, using the numbers, one round weighs about an ounce; multiplied by 3000 gives the 190 pounds and multiplying by 30000 gives 1900 pounds.

In regards to the OP, I'm still not sure of the method. The circumference of the 8-inch drum is 8π which is about 24 inches. If a round is a 0.4-inch diameter then 24/0.4 rounds can fit on that circumference, which is 60 rounds. Even less will fit on the next circumference. I don't understand how 3000 rounds will fit in the drum if they are placed on concentric circles within the drum.

What did I miss?

[Shark_Force]

The shape could dramatically alter the results. Since the choice is arbitrary, trial and error could perhaps find one that yields similar results across shapes. But those results could be absurd; for example, the radius is cubic in the volume of a sphere but quadratic in cylinders.

Adding a zero to the payload is a problem. For the SAMAS, using the numbers, one round weighs about an ounce; multiplied by 3000 gives the 190 pounds and multiplying by 30000 gives 1900 pounds.

In regards to the OP, I'm still not sure of the method. The circumference of the 8-inch drum is 8π which is about 24 inches. If a round is a 0.4-inch diameter then 24/0.4 rounds can fit on that circumference, which is 60 rounds. Even less will fit on the next circumference. I don't understand how 3000 rounds will fit in the drum if they are placed on concentric circles within the drum.

What did I miss?

the fact that the drum is a 3d shape and you can have more than one layer?

[Natasha]

The shape could dramatically alter the results. Since the choice is arbitrary, trial and error could perhaps find one that yields similar results across shapes. But those results could be absurd; for example, the radius is cubic in the volume of a sphere but quadratic in cylinders.

Adding a zero to the payload is a problem. For the SAMAS, using the numbers, one round weighs about an ounce; multiplied by 3000 gives the 190 pounds and multiplying by 30000 gives 1900 pounds.

In regards to the OP, I'm still not sure of the method. The circumference of the 8-inch drum is 8π which is about 24 inches. If a round is a 0.4-inch diameter then 24/0.4 rounds can fit on that circumference, which is 60 rounds. Even less will fit on the next circumference. I don't understand how 3000 rounds will fit in the drum if they are placed on concentric circles within the drum.

What did I miss?

the fact that the drum is a 3d shape and you can have more than one layer?

Well, yes, of course.

I can easily make it work if ammunition consumes some of the space added by the fudge factor, as shown in the example. But the fudge factor was said to be added after the ammunition computations were made.

So I am unsure of the method that was used. My only real interest in the results are that I'm able to replicate them. I've been unable to discover the method of finding the sizes from the data.

The method I used says < 600 rounds fit in the original cylinder before the fudge factor was added for non-ammunition. For the original 4 x 5.45 cylinder, you can get about 30 on the first circumference and 7 along the length of the cylinder. So you get 210 total on the first circumference. This is nowhere near enough to get 3000.

EDIT: I missed adding the word original in my previous post.
The sentence should read: "I don't understand how 3000 rounds will fit in the original drum if they are placed on concentric circles within the drum."

[Mack]

In regards to the OP, I'm still not sure of the method. The circumference of the 8-inch drum is 8π which is about 24 inches. If a round is a 0.4-inch diameter then 24/0.4 rounds can fit on that circumference, which is 60 rounds. Even less will fit on the next circumference. I don't understand how 3000 rounds will fit in the drum if they are placed on concentric circles within the drum.

What did I miss?

Keep in mind, I'm ballparking some portions of this. Some figures are rounded off because I didn't feel like going to 9 (or 15) decimal places. Here we go...

For the C-40R rail gun, a single round weighs 0.063 lbs (190 lbs drum / 3000 rounds). Using the density of Tungsten, than works out to 0.091224 cubic-inches. If I take that volume, multiply it by the 3000 rounds, and then double it (for feed mechanism, dead space, etc), I get a volume for the drum of 542.1706 cubic-inches. Assuming the drum is cylinder with an 8 inch diameter, that gives a length of 10.89459 inches.

If I take the round volume (0.091224), assume each round is a slug (a cylinder) with a diameter of 0.4 inches, then the length of a round is 0.719 inches. Compare that with the length of the drum (10.89459) and I can get 15 rounds laid end to end, with a wee-bit of space to spare. So take 3000 (total rounds) and divide by 15, and we get 200 rounds needs to fit in each "slice" of the ammo drum.

So can we get 200 rounds into each slice? For this piece we really only need to look at the end of the drum, the 8 inch circle. With each round being a 0.4 inch circle, does 200 of them (200, 0.4 inch circles) fit within the larger 8 inch circle? An 8 inch circle has a area of 50.24 sq-inches. The area of 0.4 inch circle, multiplied by 200, gives a total area of 25.12 sq-inches... which is half of the area of the 8 inch circle.

So without diving any deeper into this math, I can say that the 200 small circles will fit within the 8 inch larger one and leave room to spare. Thus we can fit 200 rounds into each "slice" of the ammo drum. And we know we can fit 15 "slices" into the drum length of 10.89459 inches.

That's 3000 rounds in a drum with an 8 inch diameter and 10.9 inch length.

And please keep in mind, this is supposed to be good enough for a gaming table. Not much more.

[Mack]

I'll skip all the math, but I used the density of Tungsten to figure out the size (volume) of each round, multiplied that by the payload, and then doubled it to account for the drum itself (feed mechanism, open space, etc). Here's the result:

A few questions:
1. Why Tungsten? IIRC isn't it supposed to be steel/iron? (though it might not even be identified AFAIK in Rifts, one of the Japanese RG's mentions using a lighter material for the round, then there is a Railgun in Robotech 2E that uses Tungsten, and what happens if you use more common material iron/steel for damage output).

Why not? I needed a heavy metal to work with so I picked Tungsten. (I briefly looked at lead and uranium as well.) It was a fairly arbitrary choice, but I needed something and there was no 'right' answer.

As for lighter materials, then the volume of each round would be larger, and so would the ammo drum.

2. Not to throw a monkey wrench into your work, but how does altering the shape of the projectile to the stated "metal spikes, balls, or rings" (RMB pg225 or RUE pg270 Railgun description) impact the results since we aren't told normally what the shape of the slug is in a given RG (AFAIK only the Boomgun-type has that specific distinction).

Good point. Yes, those shapes would have very different outcomes. Frankly I forgot about that little tidbit of info, and I've always envisioned rail guns using slugs. Especially so since they use "ammo-belts."

[rem1093]

I'll skip all the math, but I used the density of Tungsten to figure out the size (volume) of each round, multiplied that by the payload, and then doubled it to account for the drum itself (feed mechanism, open space, etc). Here's the result:

A few questions:
1. Why Tungsten? IIRC isn't it supposed to be steel/iron? (though it might not even be identified AFAIK in Rifts, one of the Japanese RG's mentions using a lighter material for the round, then there is a Railgun in Robotech 2E that uses Tungsten, and what happens if you use more common material iron/steel for damage output).

Why not? I needed a heavy metal to work with so I picked Tungsten. (I briefly looked at lead and uranium as well.) It was a fairly arbitrary choice, but I needed something and there was no 'right' answer.

As for lighter materials, then the volume of each round would be larger, and so would the ammo drum.

2. Not to throw a monkey wrench into your work, but how does altering the shape of the projectile to the stated "metal spikes, balls, or rings" (RMB pg225 or RUE pg270 Railgun description) impact the results since we aren't told normally what the shape of the slug is in a given RG (AFAIK only the Boomgun-type has that specific distinction).

Good point. Yes, those shapes would have very different outcomes. Frankly I forgot about that little tidbit of info, and I've always envisioned rail guns using slugs. Especially so since they use "ammo-belts."

We always use a sabot dart design. The dart would fill about 75% or more of the casing. Basically it would be something like a 7.62mm round would have a 5.56mm dart. The problem is the length of the dart. For that, i would go with something like a .308 or 300.

[Natasha]

In regards to the OP, I'm still not sure of the method. The circumference of the 8-inch drum is 8π which is about 24 inches. If a round is a 0.4-inch diameter then 24/0.4 rounds can fit on that circumference, which is 60 rounds. Even less will fit on the next circumference. I don't understand how 3000 rounds will fit in the drum if they are placed on concentric circles within the drum.

What did I miss?

Keep in mind, I'm ballparking some portions of this. Some figures are rounded off because I didn't feel like going to 9 (or 15) decimal places. Here we go...

For the C-40R rail gun, a single round weighs 0.063 lbs (190 lbs drum / 3000 rounds). Using the density of Tungsten, than works out to 0.091224 cubic-inches. If I take that volume, multiply it by the 3000 rounds, and then double it (for feed mechanism, dead space, etc), I get a volume for the drum of 542.1706 cubic-inches. Assuming the drum is cylinder with an 8 inch diameter, that gives a length of 10.89459 inches.

If I take the round volume (0.091224), assume each round is a slug (a cylinder) with a diameter of 0.4 inches, then the length of a round is 0.719 inches. Compare that with the length of the drum (10.89459) and I can get 15 rounds laid end to end, with a wee-bit of space to spare. So take 3000 (total rounds) and divide by 15, and we get 200 rounds needs to fit in each "slice" of the ammo drum.

So can we get 200 rounds into each slice? For this piece we really only need to look at the end of the drum, the 8 inch circle. With each round being a 0.4 inch circle, does 200 of them (200, 0.4 inch circles) fit within the larger 8 inch circle? An 8 inch circle has a area of 50.24 sq-inches. The area of 0.4 inch circle, multiplied by 200, gives a total area of 25.12 sq-inches... which is half of the area of the 8 inch circle.

So without diving any deeper into this math, I can say that the 200 small circles will fit within the 8 inch larger one and leave room to spare. Thus we can fit 200 rounds into each "slice" of the ammo drum. And we know we can fit 15 "slices" into the drum length of 10.89459 inches.

That's 3000 rounds in a drum with an 8 inch diameter and 10.9 inch length.

And please keep in mind, this is supposed to be good enough for a gaming table. Not much more.

Got it now. I misread the setup.
I appreciate your time, Mack.

[ShadowLogan]

As for lighter materials, then the volume of each round would be larger, and so would the ammo drum.

Why? We know damage assignments are arbitrary, so the lighter material using weapons might in actual practice take a hit in performance (and the AT-600's range is reduced compared to the "heavy" AT-1200 variant).

Shame that in Rifts (AFAIK) they haven't an example pertaining to using various metals for Rifts Raingun rounds that are more "detailed" like in the 2E Robotech New Generation SB (pg57). Though if megaversally speaking it is applicable to Rifts, then it would suggest that Rifts isn't using tungsten rounds (single round in RT gun made of tungsten hits x10 harder than a C-40R single round, x5 for non-tungsten) or if they are they are using lower velocity in Rifts than in RT.

Good point. Yes, those shapes would have very different outcomes. Frankly I forgot about that little tidbit of info, and I've always envisioned rail guns using slugs. Especially so since they use "ammo-belts."

Well the Boomgun illustrations do use slugs, which would match up if we where talking about the BG and apply it to other railguns and ignore contradictory text.

Spikes and Balls I can see working with an "ammo-belt", and rings might even work to if its used as a "jacket" to fire non-ferrous materials (like wood) resulting in something closer to a spike. Spikes wouldn't be much different than conventional projectiles really, so could be seen as adaptable to belt fed. Balls while different shapes, might still work with a belt feed.

[Natasha]

CWC page 121 has a rear view of the Striker SAMAS and shows the rail gun ammo drum. Your sizes seem reasonable compare to that image.

Whohoo! Dumb luck counts!

I seriously doubt the authors & artists calculated the volumes like I estimated. I consider it a happy happenstance that my figures are close to the drawing.

It gets better.

I arbitrarily decided that the unit cost of the drum's base material is 8, and the unit cost of the barrel material to be 6. I did the maths to find the least expensive drum to build for four of the weapons and I found these diameters:
SAMAS: 8.0522"
Skelebot: 6.5236"
TX-250: 8.82684"
TX-500: 6.03748"

The method is to start with the cost, set the derivative to zero, solve for r:

1. C = 8(πr²) + 8(πr²) + 6(2rl) = 16πr² + 12πrl
2. Get l in terms of r
3. Differentiate dC/dr = 0
4. Solve for r

The full description is on page 4 of this PDF. It's mostly a brainstorm still, but it could become better/usable... particularly if others contribute.