Sabot range for modern autocannons
 

It all started rather simple, going over Bushmaster 30mm Mk44 AC statistics and I had 3 references that said "over 100 mm @ 1000m 0deg." I also encountered 40mm BM and Bofors stats including muzzle velocity, travel time etc. and being what I am (computational science minor), I started digging in. So all the physics aside, I made a simplistic assumption that gravity doesn't matter to vertical speed (it does, but not much at these speeds/ranges) and came up with some fancy equations without an exact solution. Unanswered questions remained, like "is the armor penetration depending more on the momentum (velocity x mass) or the kinetic energy (½ x mass x velocity x velocity)?"

After 5 a4 papers with equations and some coding, here's the php scripts that I made:
First:
round velocity and distance (plus penetration capability as percentage of point blank range both for momentum and energy) by time, given the muzzle velocity and drag constant*) for type of ammo: http://www.venhola.com/winspmbt/sabotcalc.php

Second:
Estimate the drag constant for ammo given the muzzle velocity and flight time to distance:
http://www.venhola.com/winspmbt/sabotcalc2.php

You can use the second to estimate the value for the first and to get penetration estimates at given flight times. Unfortunately not yet for distances.

What I suspected was that the penetration capability is dependent both on the momentum (which dictates the impact peak force) and energy (which is reduced on impact due to changing form of armor) and at least for Bushmaster 30mm Mk44 AC it was almost 100% match using 50:50 division between them, so I added the 50:50 mix to the lot. I was using this data as a reference as it reflected pretty much the penetration in OOBs for 30mm BM Mk44 (120 mm @ 0m 0deg vs. approx 62 mm @ 0m 60deg).

As an example, 40mm Bofors AC - used in Swedish CV9040 - has been given table values "Muzzle v: 1.48 km/s flight time to 1.5 km = 1.1 s". The 2nd link gives us a constant c = -0.10773241083846 (last iteration result) which we feed to first. As a result for flight time 1.1s it gives:

t: 1.10s v: 1.26 km/s dist: 1.50 km momentum: 85.1% energy: 72.4 % combined: 78.7%

Suggestion there is that penetration at 1500m should be 78.7% of 0m penetration 200mm, 200 x .787 = 157.4 mm
Army-guide.com tells us "At a tactical firing range the penetrator can penetrate armor well in excess of 150 mm."
"When firing against armoured vehicles the maximum upper range bracket is between 1500 and 2000m" (The Bofors Gun, Terry Gander)
at 2km it is 72.9% or 146mm, which is again well within scope.

The problem with sabot ammo is naturally that after given range the accuracy and efficacy drops, but is the sabot range in OOBs there to keep the game balanced (sacrifice some penetration value realism for tactical realism = "don't be trigger happy @ 3km ranges") or is the sabot ranges for modern autocannons close to gun max ranges because they just used to be about the same for MBT guns? Judging from this pic the 30mm Bushmaster should have Sabot Range set somewhere 150 hexes...

*) drag constant here is in physics POV "½ x density of air x cross-surface area x C", where C is between 0 and 1 and depends on the form of the object. However, one number is enough for us.

Re: Sabot range for modern autocannons
 

Ummm ... while a LOT of real world data is used in the game a fair number of things are also generalized for play balance. Weapon ranges often being one of them. An X caliber weapon fires Y distance. Not totally accurate/realistic but in the ballpark and pretty standard across all OOB's.

Re: Sabot range for modern autocannons
 

Sure, I get that. During the years I've learned a lot on the middle ground between reality and the game balance. Weapon ranges are effective ranges to moving targets, not "fire at 40 degree angle and shot will land there" ranges.

As far as I know the sabot penetration in the game is linearly dependent on target distance but that it is not sabot_pen * (1 - distance / sabot_range), i.e. it's not sabot_pen at zero distance and 0 at sabot_range distance. From what it looks like in 30mm Bushmaster Mk44 is that it goes to 0 at around 1.5 times the max distance or so:
pen(distance) = sabot_pen * (1 - distance / sabot_range / 1.5).

Am I correct in my assumption that a longer sabot range does not allow firing at that range? The Mobhack manual does not state that definitely:
Also, if the fact is that the system is designed (and consistent between OOBs and weapons) to be a bit underpowered at longer distances (beyond 1km) then I'll have no problem with that and I will be more enlightened after learning that fact.

Re: Sabot range for modern autocannons
 

It's been too long since my Calc classes, therefore, allow me a wee bit of latitude here. Is it fair to say, the game calculates trajectories internally, the player need not elevate a weapon to fire, simply id target, and account for range and ammo type. Therefore, to the player the fires are linear, although internally the game calculates a trajectory.

After reading this thread several times, I loaded the tutorial scenario, slot 000, engaged an Iraqi tank to document what the game reports at point of impact with the following:


Please note the following values: Pen 109 (HellFire missile) Arm 21 (armor rating of T-55), @15 degrees (angle of Hellfire impact).

Now, loading up Mobhack, I find the Hull Front Armor value for the T-55QM is 20, and the HEAT Penetration values for the Hellfire A is 105.

If the game targeting is simply linear, why the angle of Hellfire impact value is reported?

So, please excuse if I've completely missed the point here, I just found the article fascinating to the point that I felt compelled to contribute my "two cents worth."

And, if someone would explain the variance in the Armor Hull, and Hellfire HEAT penetration values, as reported in MobHack and in game play, I'd be a happy camper.

Re: Sabot range for modern autocannons
 

If you want to play with new values effects then simply edit a copy of the weapon in Mobhack and then use apcalc to view the new results. The help is in a text file called armourcalc_help.txt - read it!.

I usually copy the original weapon to a free bit of space in the weapons list, then copy the new one under it from the original as well. That saves having to scroll about to find things for comparisons. Retitle to something like TEST 001 so its easy to find and to kill it later, when done with testing.

The MBT_ or WW2_APcalc utilities live in your home game directory.

NB - the utility is not 'live' - so close it and reopen it to load any changes you make in mobhack.

Re: Sabot range for modern autocannons
 

Thanks, I've already tried and tested that before drawing any conclusions. I was a bit unclear on the "sabot linear range", what I meant was that the sabot penetration depends linearly on the distance. Using MBT_APCalc.exe I pretty much drew this conclusion thru series of tests.

Still the unanswered big question I'm having is that is the sabot penetration deviation from real world tests a game balance design issue or is it that recent technological advances in APFSDS ammo have not yet been carried to the game? (Or 3rd option: something completely different)

I'm trying to gather more data about different guns and ammo types just to dig to the bottom of this. However, lack of public data is a hindrance.

Re: Sabot range for modern autocannons
 

You wont be told anything about the formulae since they are proprietary to SSI and not to be revealed (part of the agreement when the code was released).

Therefore - its up to you to figure it out as to how it fits your expectations.

As to public data - all lies and and manufacturers advertising. hard data is difficult enough to find for WW2 era ammo, and modern stuff is current and hence classified.

Re: Sabot range for modern autocannons
 

The entire exercise is pointless . These are direct fire weapons . The maximum range for direct fire weapons in the game is 99 hexes max because 99 is the max visibility of the game and that isn't ever going to change and for probably >99% of the generated games the visibility will be UNDER the max range of any tank / IFV weapon in the game anyway so the question has to be asked.... what's the point of saying "the 30mm Bushmaster should have Sabot Range set somewhere 150 hexes" when that's 51 hexes further than you can set the games visibility ? All ranges >99 for direct fire weapons are pointless ( yes, there are lots and all pointless because 99 is the max visibility that can be set and therefore the max range you can shoot them )

There's a similar issue with aircraft weapons ranges...... aside from standoff weapons the nominal 40 hexes a lot of aircraft weapons get amount to eyecandy because aircraft in the game only ever engage targets at < 1/4 that range

Re: Sabot range for modern autocannons
 

One of the questions in the very first post condensed into one sentence:
Is the maximum range for a gun to shoot sabot rounds the actual "range" value even if "sabot range" is greater?

Another quick question still unanswered:
Is the low penetration at ranges longer than 10 hexes a game balance issue or OOB data issue?

My main issue here is the deviance from real world penetration values in usable ranges, between 20 hexes to 40 hexes and using sabot range adjustments for fixing that (the way sabot range adjustment has usually been used to decrease the effectiveness).

As for the formulae I do know that they're the trade secret yet we can check the outcomes using mbt_apcalc for example. Or setting up a gazillion scenarios and write down the results of our shots.

Of course manufacturers put up the results they have gotten when shooting in the perfect conditions with pre-warmed rounds in low atmospheric pressure and brand new barrels targeting 2nd grade RHA targets. And different testers get different results. Still we get the ballpark figures over there.

Re: Sabot range for modern autocannons
 

APCalc uses the games code to show penetration values so running tests at various ranges and comparing them to whatever source you trust will give you the answer about how close we are to whatever penetration reality they are claiming their weapons will do. REMEMBER there are a HOST of variables that effect penetration so you need to run the tests a good dozen times to see the highs and lows but APCALC only deals with normal penetration variables not the random factors the game throws in after the fact and when all is said and done I'm not going to change any data unless more than one source proves we have incorrect values so I'm not the least bit interested in theoretical penetration of say..... 8cm at 2000 meters when it works out to 7 or 9 in APCalc show me we are grossly out and I'll pay attention

Re: Sabot range for modern autocannons
 

I've now done some early analyses and come up with the following findings:

• Bofors L70 40mm has two generations of APFSDS ammunition with differing penetration values.
• Bofors L70 40mm APFSDS ammunition has exceptionally low drag (the penetrator may fly up to 40 km!)
• Penetration data (Bofors 40mm L/70) for differing distances and ammunition generations is hard to find from reliable sources. Unnamed sources agreeing may have a common ancestor.
• Bushmaster 30mm APFSDS has a low drag, but not as low as Bofors L70 40mm's.
• Rheinmetall 120mm APFSDS data on OOB is in accord with the calculations
• This model works well only when the projectile has at least Mach 1.1 speed. All bets are off after that point.

The good news here is that because the model predictions for tank sabot ammunition is well within margin of error in the source data: for Rheinmetall 120mm L/55 DM53 the sabot penetration @3km is modeled at 676 mm vs. 660 mm in the MBT_APCalc.exe. Closer distances are even better aligned, for example @1km 854mm vs. 860mm. This gives me confidence that the model isn't grossly off.

Further checks I made were to check the NSV 12.7mm values given by MIL-STD-662F p. 20. The predicted velocity and observed velocity are within 2.25% of each other. I.e. the small caliber should not affect.

I'll continue with Russian autocannons to see if they follow the suit and the OOB and the model agree there. Then we can say that it is the low drag of these and only these projectiles that require tweaking.

Re: Sabot range for modern autocannons
 

We had confidence in the game model years ago ..... but you have fun

Re: Sabot range for modern autocannons
 

To clarify, by model above I mean the model I wrote. And BMP-2 2A42 again fits the data and the game data - with a small nuance which I'll address later in the wrap-up (3UBR8 penetration @1.5km). What it looks to me is that the recent APFSDS ammunition has lower drag which can be represented by giving higher sabot range values in OOBs, just as I suspected in the first message.

I'll make a proper post with findings and sources listed later.

Re: Sabot range for modern autocannons
 

Not sure what you are getting at here
1) If like a tank main gun the range is often 100+ for sabot the shot will never be taken because the hit probability is to low.

2) If what you want to know is if sabot will fire past its range which I seriously doubt then just adjust the sabot range to say 15 & see what happens when you fire at a target at range 16 hexes.

3) Just guessing but sometimes the sabot range might be massaged slightly so the formula gives penetration results that more closely match RL results.
Adjust the range of weapons & look in AP Calc if you want to reverse engineer the formula used.
Penetration of a 100 would probably make the results fairly simple to read.

Re: Sabot range for modern autocannons
 

Keep in mind that a weapons max range effects it's hit probability, a weapon with a 120 max range will be somewhat more likely to hit at any range then one with a 100 max range.
And the "sabot range" has significant effects on sabot penetration.

Re: Sabot range for modern autocannons
 

After noticing that the CV9030 Bushmaster Mk44 AC penetration at longer distances felt too low compared to what I had read I made some serious dive into the wonderful land of APFSDS penetration theory and measurements. I compared the numbers to other autocannons starting with Swedish Bofors 40mm L/70 autocannon used in CV9040.

Contrary to what I stated in the first post I found out that the penetration doesn't depend linearily from momentum or kinetic energy. All other factors being stable the penetration of RHA is proportional to the e^(-1/v^2), where v is the velocity and e is Euler's number (a.k.a. Napier's constant).

When I had gathered the data all around the Internet I found out that the game formula works really well for every other gun than the CV90 guns. I also found out couple of oddities in the OOB which should probably be corrected anyway. The CV90 guns have what is advertised as low drag kinetic penetrators and they seem to retain their penetration capability rather well.

Bushmaster 30mm (note: ammunition may vary on Warfaretech values from others)
Penetration in mm.
http://www.nammo.com/globalassets/pd...g_2014_web.pdf
https://www.doria.fi/bitstream/handl...pdf?sequence=1 (In Finnish)
http://warfaretech.blogspot.fi/2014/...ic-cannon.html
* = Thesis gives penetration values for three ranges, which makes the penetration figure probably overestimating at the long end (1500-3000m = 80 mm)

From these values and the Nammo given muzzle velocity I calculated the drag constant c = -0.1145. Using that drag constant and penetration-velocity equation fitting the data to the mathematical model gives the following estimates for penetration:
This data is really well in line with the penetration figures given earlier.
If the penetration @0km is kept at 120mm (OOB Sabot pen: 12) then bumping the Sabot Range to 160 would give the closest response to RL penetration tables:

The Swedish Bofors 40mm AC had data which seemed to contradict itself until I found out that Swedes have upgraded the APFSDS ammunition in 1997 and again in 2005! Luckily the 1997 change was only to make the round safer for the CV90 crew. Also the data is hard to find, so I only have a couple of sources.

For the 1997 revision Bofors 40mm Slpprj 90LK/97 (Assumed that weapon slot 016 in Swedish OOB is this one, pen=20, sabot range=60)
Muzzle velocity: 1,470-1,480 m/s
"The flight time to 1500m is less than 1.1 seconds." (Gander)
Drag coefficient is thus c=-0.1077 which is almost 10% better than above.
http://www.dtic.mil/ndia/2003gun/boren.pdf
The Bofors Gun by Terry Gander
http://web.archive.org/web/201311150...om/protect.htm
http://www.steelbeasts.com/sbwiki/in...mmunition_Data
* = Reliability questionable

Assuming the 131mm and the initial velocity and flight time are correct I was able to work back to following penetration tables:

Assuming the higher, 140 mm @1km penetration figure we can deduce a safe upper bound:
Adjusting the sabot penetration to 15 (150 mm) and giving sabot range 130 we would reach
The current round used by Swedes, Bofors 40mm Slpprj 95LK/05
Muzzle velocity: 1,510 m/s
The penetrator is heavier and faster than 1997 version.
Assuming the same drag coefficient as earlier.
http://www.army-guide.com/eng/product3367.html
http://www.dtic.mil/ndia/2003gun/boren.pdf
http://www.odbrana.mod.gov.rs/arsena...senal%2048.pdf (in Serbian. Uncertain whether this is a different round, also muzzle velocity stated differs)

Here we assume the 170mm is a good number (shouldn't be less than 160 anyway) and work the equations:

Adjusting the sabot penetration to 19 and giving sabot range 150 (gasp!) we would have
Which gives slightly lower results around 2km range but it is acceptable as range is anyway so far away that hit probabilities are getting too low to try it.

For this post I made careful checks with other weapons as well:
120mm DM33 L44
120mm DM53 L55
120mm DM63 L55
30 mm 2A42 3UBR6
30 mm 2A42 3UBR8

and all the real world data was well-aligned to the model predictions and OOB penetrations... with an anomaly I found:
BMP-2 uses 2A42 30mm autocannon which has poorly performing AP and sabot rounds (in real life as well as in the OOB). The AP round often used - Finland as well - is (APBC-T) 3UBR6 for which has AP pen 6 and range 80. Then there is a sabot round, APDS 3UBR8, which has sabot pen 8 and range 40. Jane's gives the following penetration data
Rosonboronexport catalogue says
for 60 deg impact. This would translate to 40 and 50 mm but compared to Jane's numbers there seems to be marketing extra in here. Anyway the ~50mm is far from the game given 30mm @1.5km which seems to be a result of a round up as game gives 20mm @1.55km. This lead me to think that the 25mm result has been taken as 0 degree impact as this APDS round has worse performance than the APBC round. The sabot range should probably be bumped up as well.

MODIFY
BMP-2 2A42, multiple nations
Sabot range should be higher, penetration @1.5km approx 40mm

MODIFY
Bofors 40mm L70 AC, Sweden
Starting 2005 the sabot values should be
pen: 19
range: 150

before that
pen: 150
range: 130

to represent the low drag with high sabot range.

MODIFY
Bushmaster 30mm Mk44 AC, multiple nations
sabot range: 160
or alternatively
bump up penetration to 13
range to 130

Note
For all you other nerds over there, math (and physics) is in the attachment.

Re: Sabot range for modern autocannons
 

For some reason the attachment refused to attach. Downloadable at http://www.venhola.com/winspmbt/velocity_and_drag.pdf

Re: Sabot range for modern autocannons
 

EEK! Please tell me thats a typo!

Re: Sabot range for modern autocannons
 

:D

Yes, it's sometimes hard not to mix the penetration values in OOB (in tens of mm) and penetration values elsewhere (in mm). It's supposed to be "pen: 15"