Alternative BV for Ammo-dependent Weapons

[Retry]

This came from a discussion/mini-rant on ammo weapons and the peculiarities of them and their BVs (HAG-40s with a very limited single ton of ammo costing around 600 BV, its BV goes up crazy amounts for a well-stocked gun, swapping some big LRM racks + ammo for lots of smaller LRM-5 racks + ammo can reduce your BV cost since the LRM5's ammo is cheaper, etc).  Basically, typical BV criticisms under hyper-critical eyes.  Anywho, the point is that I was challenged to try to make a better system.  So, here's my attempt for a better, more useful BV calculation for ammo weapons.


Current Implementation
The current implementation is found on Heavy Metal Pro's empirical weapon BV formula:
https://www.heavymetalpro.com/bv_calc.htm

Essentially, the BV is determined by summing the average expected damage of the weapon across all range brackets, and multiplying that sum by a factor (1.2 for non-energy, 1.5 for energy).  The BV for ammunition is a flat 1/8th the weapon BV.


Suggested Implementation
I suggest to diverge from that by changing the multiplication factor of non-energy weapons to 1.5, the same as energy weapons.  This value will be called the "Base BV", or BASE and it can be roughly estimated from current weapon BVs by multiplying existing weapon BVs by 1.25.  Ex: a 100 BV ammo weapon becomes about 100*1.25=125 BV.

EXAMPLE: The new BV for the AC/10 becomes 123*1.25=153.75 -> 154=BASE
EXAMPLE: The new BV for the UAC/10 becomes 210*1.25=262.5 -> 263=BASE

Instead of having ammunition BV separate from the weapon, the amount of ammunition is factored into an "Ammo Factor" that's dependent on the unit mounting it:

AF=(1-.5^.2*X)
Where X is the number of rounds the weapon(s) can fire before the magazine runs dry.

EXAMPLE: A mech with 1 AC/10 has 0 rounds of ammo.  X=0
The AF is (1-.5⁰)=0
EXAMPLE: A mech with 1 AC/10 has 10 rounds of ammo.  X=10 ammo/1 shots per round = 10
The AF is (1-.5²)=.75
EXAMPLE: A mech with 2 AC/10s has 10 rounds of ammo total.  X=10 ammo/2 shots per round = 5
The AF is (1-.5¹)=.5
EXAMPLE: A mech with 1 UAC/10 has 10 rounds of ammo, or 5 rounds rapid-firing.  X=10 ammo/2 shots per round = 5
The AF is (1-.5¹)=.5

The final BV for the weapon is calculated through the following formula: FBV=BASE*AF

EXAMPLE: The BV for an AC/10 with 0 rounds is BASE*AF=154*0=0
Normally, the BV would be 123.
EXAMPLE: The BV for an AC/10 with 10 rounds is BASE*AF=154*.75=115.5 -> 116
Normally, the BV would be 138.
EXAMPLE: The BV for 2 AC/10s with 10 rounds total is BASE*AF=308*.5=154
Normally, the BV would be 261.
EXAMPLE: The BV for an UAC/10 with 10 rounds is BASE*AF=263*.5=131.5 -> 132
Normally, the BV would be 236.


My case for the alternative method
The current method for ammo-dependent weapons has two primary issues.  The first is that it bases ammo BV directly off the BV of the gun and over-inflates the BV of large weapons vs small ones, and the second is that the BV of additional ammo is assumed linear which doesn't take into account diminishing returns and hurts guns with low ammo/ton counts.  This alternative method fixes both.

Ammo BV in the original method is calculated simply by dividing the weapon's BV by 8.  While simple to calculate, it's not actually very accurate in estimating the value of that individual shot.  Consider the venerable LRM Carrier: 3 LRM-20s and 4 tons of ammunition, 833 BV.  If one were to field-modify the LRM carrier to use LRM-5s instead, the modified LRM carrier could have 12 LRM-5s (60 tubes, same as original) and 10 tons of ammunition (150% more), 798 BV.  The firepower of the modified LRM carrier is equivalent, and it has a massive advantage in both endurance and alternative ammo types due to the cavernous ammo bay, yet the BV is lower than the LRM-20 model exclusively due to the much lower BV of the LRM-5 ammo.  My suggested method would fix that issue completely: the 60 tube array with a lot more ammo would have a higher BV than the 60 tube array with less.

The simple linear model also gets in the way of large weapons by not taking into account diminishing returns.  For instance, taking the HAG-40 from 3 shots to 6 shots costs 67 BV.  It also costs 67 BV to take the HAG-40 from 15 shots to 18 shots.  The first instance is basically allocating the absolute bare minimum amount of ammo needed for the weapon, while the second instance is fluffing up the ammo bays to help it perform well during long battles.  Clearly, the additional 3 shots in the 1st case were more valuable for the system than in the 2nd case.  Other weapons are high on BV and low on ammo, such as the Thunderbolt-20 and iATM-12, need to allocate a lot of ammunition to keep the gun usable in the long-run, further inflating their BVs above their actual value.  This proposal solves that issue by basing the weapon's BV off of the number of shots it has instead.

In addition, notice that in this proposal the formula for ammo-dependent weapons, notice that the formula for the BV of energy and non-energy weapons become essentially identical, the only difference being that the ammo weapons have an additional "Ammo Factor" built in to the equation.  Also notice that as the number of shots allocated to the ammo weapon approaches huge values (X approaches infinity), the "Ammo Factor" approaches 1 and the formula becomes the same as that of an energy weapon, which for all intents and purposes are weapons with infinite ammunition.  That result is not a coincidence!

Feel free to comment or ask me questions on anything.

[Retry]

Now that I have a bit more time, I added more detail into the OP and more examples, and also added a few paragraphs giving my case for the suggested changes.

[Col Toda]

No point . Their is an excessive  ammo rule . Once your tonnage BV equals  the BV of the weapon the BV of ammo beyond that is ignored . True in some cases it is like after the 5th ton of ammo the excess ammo  beyond that is ignored in the calculus.

[Retry]

No point . Their is an excessive  ammo rule . Once your tonnage BV equals  the BV of the weapon the BV of ammo beyond that is ignored . True in some cases it is like after the 5th ton of ammo the excess ammo  beyond that is ignored in the calculus.

I believe you're referring to the "excessive ammunition" rule on Tech Manual, pg. 303:

Excessive Ammunition: To prevent excessive ammo from distorting the Battle Value, the BV added for ammunition cannot exceed the unmodified BV of the weapon itself. If the BV of the ammo exceeds the weapon BV, reduce the ammo BV to match the unmodified weapon BV. When a ’Mech carries several weapons of the same model, total the BV for that model and the ammunition carried before comparing the two BVs.

The excess ammunition rule applies once the BV of the ammo exceeds that of its corresponding weapons.  Since the BV of ammo is 1/8th that of the weapon itself (plus-or-minus due to rounding errors), it takes 8 tons of ammo per weapon to reach the excessive ammunition limit.  That's a tad bit more than just 5 tons of ammo.

Example: HAG/40 is 535 BV.  A ton of HAG/40 ammo is 67 BV.  8 tons of HAG/40 ammo is 536 BV.  So if you're packing four minutes of continuous fire in that HAG/40, you save a grand total of 1 BV due to the rule, not enough to buy a cup of coffee.

I'm genuinely struggling to find a case where literally any ground-based (or space-based) unit is packing that much ammunition.  Canon, apocryphal or player-made designs.  There's just no need for that much ammo, ever.  The absolute closest I can think of is the Aesir Medium AA Vehicle (HAG), six tons of ammo, which still doesn't reach that cap.  Maybe there's an Arrow IV or Long Tom custom out there with that truly cavernous ammo bay, but that's a real edge case.

Unless you count the Buffalo Drone Bomb, by a technicality (no weapons, still has ammo).

In any case, the ammo problem I highlighted comes into effect far earlier than 8 tons of ammo.  Yeah, that rule exists, but it's like water intoxication: you're not actually going to hit it unless you're specifically trying to hit it, so it's functionally irrelevant in every-day Battletech.


Although, this discussion does bring into my mind another example:

Compare the Large Laser (BV 123) to the Large Chemical Laser (BV 99, Ammo BV 12).  Virtually everything is identical except one requires ammo.

At 0 tons of ammo (IOW empty), the canonical formula records the weapon BV as 99, my formula records the weapon BV as 0.  Zero is closer to reality of the value of a laser with an empty magazine.

At 1 ton of ammo, the canonical formula records the weapon BV as  111, my formula records the weapon BV as 92.  10 shots is decent for short fights but not enough to waste on unlikely shots which the large laser can take all day.  The canonical formula Chem Laser is within spitting distance of the vanilla Large Laser, just enough to buy a low-end PBI squad.  My formula more closely captures the slight-to-moderate disadvantage the Chem Laser has which can make or break a game.

At 2 tons of ammo, the canonical formula records the weapon BV as 123, my formula records the weapon BV as 115.  20 shots is a good number, you can even use it on highly unlikely shots, but in very long matches or persistent scenarios you can still run a risk of running dry.  Because of that, a regular Large Laser is still slightly more useful than a Chem Large Laser with 20 shots, and not equal like the canonical formula implies.  My formula does a better job of showing that very slight difference.

Finally, let's go full ham at 8 tons.  There is no practical reason for 8 tons for one Chem Laser since at that point you could just throw in some heat sinks and get a regular Large, but let's assume this is some backwater defense satellite that no one cares about.  Anyways, with so much ammo the satellite (or a Mech boondoggle or whatever) can fire to its heart's content, so it doesn't really have any disadvantage compared to the vanilla Large Laser (other than the obvious one of a gargantuan 8 tons of ammo dedicated to a 5 ton weapon).

Anyways, the canonical formula records the weapon BV as 195.  My formula records the BV as 123, exactly the same as the regular Large Laser.  Obviously, even with the huge ammo bay the Large Chemical Laser isn't going to be more valuable in combat than the regular Large Laser.  And it's certainly not going to be better than a PPC! (BV 176)  Clearly, my formula yielded a more useful figure than the canonical one.

Yeah, I know, the first and last of those are very much silly edge cases.  But even with the more normal cases like 1 and 2 tons of ammo, my formula yielded more realistic and useful results than the canonical formulas did.  BV is an attempt to provide a single numerical rating to represent the capabilities of 'Mechs and weapons.  My suggestion formula improves the usefulness of the result for ammo-dependent weapons, even for the edge cases.

That's my point.

[killfr3nzy]

Can't say I've done the math myself or anything, but the argument as presented here makes sense to me.

For what that's worth.

[monbvol]

I do have one question.

Then SUBTRACT the following figures. These subtractions cannot drop the running total below 1.
15 points per critical space of explosive ammo in the center
torso, legs or head (Clan ’Mech)
15 points per critical space of explosive ammo in any location (Inner Sphere ’Mech with XL engine)
15 points per critical space of explosive ammo in the center
torso, legs or head, or not protected by CASE* in its location (Inner
Sphere ’Mech with Standard or Light engines)

Do you intend to incorporate those factors in some way as well?

[Retry]

I do have one question.

Do you intend to incorporate those factors in some way as well?

That's a good question.

I'd leave that part in there, as that pertains to the battlemech's Defensive Battle Rating.  The Alternative BV for Ammo-dependent Weapons is for weapon BV and the Offensive Battle Rating associated with ammo weapons, so I would say changing any other things is outside the scope of this topic.

[monbvol]

Then I'd say it looks good.