ISU-152 Current Optics - In case you were wondering.

[jeffduquette]

I don't know if the game engine has an exterior ballistics model that deals with systemic error or not. If this info is needed for proper modeling of the SU-152 it is as follows:

152mm BR-540 AP
Probable Error in height = 0.21-mils
Probable Error in Deflection = 0.27-mils

152mm OF-530 HE\Frag to 2000meters
Avg PE in deflection is constant at 0.47-mils
PE in height varies a bit more with range
PE @ 400m = 0.24-mils
PE @ 1000m = 0.28mils
PE @ 2000m = 0.38mils

I assume ranges in excess of 2Km can't be handled within the current game environment. At least I have never been on an RO game map where I could see out to more than maybe 1600m or so. But if this isn't true I can post dispersion data for shoots in excess of 2Km.

 

[Shurek]

Hi Jeff,

Yes, there is rudimentary code provided for spread, although it is not controllable to the degree that you describe in those dimensions. From my observations, the spread feature is not currently used on any of the stock RO tanks (although I could be wrong - it certainly wasn't used on the IS-2)

 

[jeffduquette]

Maybe this helps (Maybe not ) -

From the SU-85 manual (1943)

The caption says (loose machine translation): "Pic. 25. The diagram of laying the crosshair for the 10Т-15 sight to shoot at a tank at a range of 800 M and the lateral adjustment. (Tank moves from left to right)."

So 12-mil lead. Interesting that even with the applied lead, the point of aim\crosshairs are placed at the front of the target rather than center of visible mass.

 

[jeffduquette]

Hi Jeff,

Yes, there is rudimentary code provided for spread, although it is not controllable to the degree that you describe in those dimensions. From my observations, the spread feature is not currently used on any of the stock RO tanks (although I could be wrong - it certainly wasn't used on the IS-2)

Ok. Thanks. Can you point me to a thread that disscusses how shot dispersion is handled by the RO game engine? I feel like from my own gaming experiance that some inherent shot error is occuring -- at least at longer ranges. But this may be my imagination.

 

[Amizaur]

OK, finished them today.

Two textures for stock RO ISU-152's gunsight, based on picture posted on ISU-152 optics thread. Textures are based on stock RO T-3476 sight (creative copy/paste work). Ment for basic versions of vehicles, not AB (scales are not in any way synchronised with shell ballistics and drop). You can use them for ISU-152 if you find them good enough, or modify using as starting point, what you like. The second one is scaled 20% down (the CT-10 zoom was 2x, TMFD zoom was 2.5x) which gives more realistic look and gives more room for scales and labels, if it turns out that it's too small to be readable, then larger version can be used - almost copy ofT-34/76 sight, so the size should be ok.





The textures in DDS format are here:

http://www.zshare.net/download/7972809e94bac2/

(not tested them in game yet, will try that tomorrow)

To use them, first a correct AddedPitch value has to be found (will be different than for T-34/76 or KV-1), then the OpticalRanges values in shell class have to be found for this sight to work smoothly. On the end the MechanicalRanges values found for the shells to hit targets. Much more work than using simpler sight types (PG-1).

As for me suspecting that the left scale is ment for BR-540B projectile and not BR-540:

Of course I do not say that the shell used in RO's ISU-152 shold be BR-540B !! It should be BR-540 AP.

In the manual we had before (for ISU-152M and ISU-152K) the BR-540B projectile is shown as example of an AP shell. But war-time ISU-152s used BR-540 of course.

I know BR-540B is mostly post-WW2 projectile (some claim it was available from 1944, I do not know). But the sight, scales and whole manual - source of the picture - can be post-war also - the scales may be from ISU-152M for example...

The main reason for me believeing that left scale is ment for BR-540B, is that the scale is used also for OF-540 on reduced charge. Those two could have ballistics so close that single scale was OK for them.
BR-540 have to have very different ballistics from both BR-540B and OF-540 . The first two have same weight and muzzle velocity, but totally different ballistic coefficients so physically the same scale can't be used for aiming with both BR-540 and BR-540B directly.

One of them have to be fired using conversion table. And this would be BR-540. Why do I think that, I described earlier.

But the fact that the scale is (and could be, even from the beginning in 1943) ment for BR-540B, doesn't mean the BR-540B was available. Other tanks used shells for which they didn't have dedicated sight scale, they just used one of existing scales with conversion table. Examples are IS-2 firing BR-471, T-34/85 firing BR-365K (and probably BR-365P too, no scale for it in early TSh-16), even T-34/76 and some (if not all) AP shells. So everything is perfectly OK with that, historically. And vice versa - IS-2 TSh-17 sight had scale for BR-471B shell, even though it was not available (reportedly) from the beginning (there were problems with production or quality or something) and arrived only in late 1944 (IIRC).

Jeff, thanks for the info about 152mm shell dispersion !!!

152mm BR-540 AP
Probable Error in height = 0.21-mils
Probable Error in Deflection = 0.27-mils

Is this on close range only ?

0.27 mils on 1000m gives 0.27m, on 3000m it would be 0.81m.

Values for 122mm L46 gun are 0.3m at 1000m and 0.9m at 3000m (using AP shell).

It turns out the 152mm short L32 gun is sightly more accurate than 122mm L46 gun... :-? For a very heavy shell fired on very powerfull charge...

MAYBE possible explanation is that it's possible on the test range with test gun and test sight in test bed... the balistic tables are, made in controlled conditions, it's almost pure dispersion of the barrel itself. How such powerfull gun performs when mounted on a vehicle, we can only guess...
100mm gun was mounted in T-34/85, but was found to be so inaccurare that project was abandoned...

P.S. There are good reasons the spread is not used on stock tanks (for tank shells). It causes some issues that could be called bug in commercial game, but IMO acceptable in a mod, so I chosed to use it and observe how it works, while thinking about some workaroud.

 

[jeffduquette]

The dispersion data is the average for BR-540 out to 2000meters. When you look at the actual PE provided in the FTs you will note that they are rounded down to the nearest tenth of a meter. The artifical effect of this rounding is this odd step wise depiction of dispersion vs. range. Which is of course physically impossible -- but is simply a function of rounding down. For me it is better to plot it out and determine average error in terms of mil spread. Most modern FTs detail depersions in terms of mils (and if they don't, they should ;o), and it is easier -- at least for me -- to back calculate hit probability when dispersion is expressed in terms of mils and probable error. I didnt look at ranges beyond 2000m because these are not available from the BR-540 FTs; and because I don't think the current game engine allows LOS to extend beyond maybe 1400m to 1600m.

For example here are the vertical PEs for BR-540 in meters as presented in the July 1944 firing tables for the SU-152.

100....0.0
200....0.0
300....0.1
400....0.1
500....0.1
600....0.1
700....0.2
800....0.2
900....0.2
1000...0.2
1100...0.3
1200...0.3
1300...0.3
1400...0.3
1500...0.4
1600...0.4
1700...0.4
1800...0.5
1900...0.5
2000...0.5

Normally I'd plot these out and post a graph to the thread showing P.E. in meters and the average P.E. in mils. But this forum gobbles any posts in which I try to include an image. It makes it rather difficult to communicate information of any real importance or of any real interest. I'm left to babble on with no pictures (and it's not like I haven't been posting images to forum threads for the last 10-years).

Drag experianced by OF-530 and BR-540 would obviously differ. The CRH and thus nose\head length of the two aren't even close. BR-540 having a very blunt CRH is therefore in theory going to have a much higher form factor and much lower B.C. than OF-530. This should all in theory equate to BR-540 being the less efficient ballistic shape. But it is being fired at full charge minus one increment. OF-530 -- when using the left reticle -- is No.1 Charge. Mv is much lower for OF-530 at Charge-1 than BR-540 at full charge (-)1 increment. You simply need to plot trajectories to see where match lines are occuring for various matching superelevations. This will tell you where the reticle begins to loose accuracy with respect to shoots with OF-530 and shoots with B-540. That is assuming the left reticle is designed with the OF-530 in mind.

The FTs for BR-540 say something to the effect "Direct Fire Against Tanks at 700-meters". However the FTs for BR-540 are detailed for shoots out to 2Km. One could read alot into the 700-meters comment at the top of the tables. It could suggest loss in accuracy at range beyond 700m due to the CT-10 (left) reticle...i.e. the reticle is geared to the ballistic foibles of the OF-530 projectile. But perhaps the left reticle handles shoots for BR-540 out to 700m with reasonable accuracy. Again, this sort of thing is easy enough to work through if one wants to plot trajectories for the two projectiles for various matching superelevations. Just how detailed is the exterior ballistics model for the game? I presume it is not that detailed.

The long and short being there is nothing in either the field manual nor the FTs suggesting BR-540B was available during this time period. To expand a bit on this, the field manual details armament in both the ISU-122S and ISU-152 and is dated 1950. The FTs -- as I have indicated above -- are from July 1944. While the ISU-122S portion of the field manual clearly distinguishes between BR-471 and BR-471B, there is no reference to BR-540B in ISU-152 section of the manual -- only BR-540.

Historical conjecture is always interesting, but of course this is just a game, or a modification of a game. If your game mod is made funner for you by including BR-540B than you should include BR-540B. For me, it makes little difference as I only like playing in the T34/76 or T34/85

Best Regards, and good luck
Jeff

 

[Amizaur]

Thanks for this long reply Jeff !!

We are taking not entirely about a game, I'm also interested in those matters as they were historically (ballistics, physics, gunsights, historical performance). Sure most of the details are not worth including in RO (maybe in different, more sim-like tank game), but they are very interesting to know anyway.

I did something similar that you, with the aiming error tables I had, when I was estimating tank gun accuracy for RO, only I prefer graphs



I took Russian data from tables, and ploted graphs from them, I could then estimate average mil error, at least for closer ranges, used in RO. I didn' use all (every 100m values) in this case, but I did also every 100m graph too see how it looks like. It's quite smooth, but on the other hand the side-drift graph is very steppy and it's hard to tell anything about what function could model it... (only two steps out to 3500m).

Dispersion data for German shells - I did not have them, I seen some data on old Battlefront forums, mostly I reverse-eingeered (again, with help of some posts of a guy called Rexford, how he did it, and refreshing my own knowledge of statistics) the German guns accuracy data against standard 2.5x2m target that can be found (on Guns vs Armor site). Also did it the other way - using the same target size and same metodology of statitical formulas, I did "Russian gun accuracy tables" from dispersion data:

You said about BR-540 fired on almost-full charge at 600m/s, and OF-540 on full charge on 655m/s. I admit that I thought the charge for BR-540 is slightly higher than full (it's called "special" ?) but after reading what you wrote I did a quick check and indeed, the OF-540 on full charge have higher kinetic energy on launch.
Probably the charge was reduced because full charge with 48kg projectile would generate pressures i exceed of maximum on the barrel ?

I can't find now at what speed the OF-540 was fired on reduced charge. From memory I believed this was 605m/s, but you say the speed was much lower (than BR-540?) so what was muzzle speed of OF-540 on first charge really ?

My point about same muzzle velocties (of BR-540 and OF-540 on first charge - as I supposed) is, that when you have two projectiles, having same muzzle velocity, but different ballistic coefficient, then a single scale can work very well for them up to some range, then they become more and more different slowly. But when you have different muzzle velocities from the start, then the trajectories become differ significantly much sooner, and the effective part of gunsight scale on which it can be used for "direct" aiming, is at least shorter...

In all examples I seen, when there was single scale used for aiming with several different projectiles, it was very preferable to have at least same muzzle velocity, even if BCs are different.

So what really was speed of OF-540 fired on first charge (for the left scale) ? (IIRC 540 ...? You wrote OF-530 ?? is that a typo ?) Was it around 600m/s as I remembered or even lower ?

And your point about the scale being "direct" only to some range (like 700m) may be very well the explanation why we believed the CT-10 was scaled only to 700/900m for direct fire !!!!! Didn't thought about this explanation, but with your quote from manual "direct firing up to 700m" all parts of the puzzle becomes to fit perfectly !!!!! It was scaled for 5000m, but used for "direct" fire, in meaning of direct firing/aiming, could be only to 700m after which range the trajectories were too different... (and a table would have to be used for aiming, and with questionable accuracy).

So you have really a 1944 SU (not ISU) 152 manual !! and the CT-10 picture is really of early war-time (and eben SU-152) sight, not an modernised or later-rescaled one.

You have cleared everything with one post

BTW, wait a moment... now after your last, somewhat technical, post, something ringed in my head about the nick "jeffduquette"... eee, that I possibly seen it before.... on some VERY interesting forums/threads, I couldn't join because threads were years-old unfortunately... (just as my favorite game). Well, it's my pleasure to meet you, Jeff

I sent you a PM, some time ago, here on RO forums - have you got it ? I would send you something (if it happens you don't have it yet)


P.S. I ensure anyone that I do not want to see BR-540B projectile in RO
I say again, I know it was post-ar projectile. I only mentioned it because I supposed the left scale is ment for BR-540B and not high-drag BR-540. Which can be wrong if I have wrong data about OF-540 muzzle speed at first charge...

But, note - here for the "example" shot the sight for a 3000m !!!!!! shot is set "directly" - exactly for the "30" mark. I'm quite sure BR-540 and OF-540 trajectories would differ already maybe by hundreds of meters at 3000m range... at any muzzle velocity... Now what ? Was that ment really to be "300m" AP shot, or is that HE shot agains a distant vehicle ? :| Or a "totally abstract example" showing only how to lead shots ?

 

[mlespaul]

realism...now if we could only get the vehicles to run over/through trees...ouch ....cheap shot drive-by....

 

[jeffduquette]

Test

 

[jeffduquette]

I don’t want to go too far down this road as there were two sets of charges being employed during this time period – an old type and a new type construction. And the various base charge and increment weights and myriad of restrictions regarding which charges could be employed with which projectile and which gun types; or whether or not the gun included a muzzle break; or if the propellant is granular type 18 relative to powder temperature. These all make for eye glazing reading and these sorts of details are clearly beyond the scope of game modding. Suffice to say that the BR-540 “special” charge for AP included only one big base charge and no increments. It was distinguished from the normal charge by special markings and later by a large black circle painted around the mouth of the case.

However, BR-540 could also be fired using the “normal” full charge less one increment. The “normal” full charge includes one base charge and eight smaller increaments. In other words, using the normal charge to fire BR-540 would be 8 – 1 increments = 7 increments + the base charge. But the resultant propellant weight of the “special” AP charge is identical to the propellant weight of the Normal Full charge less one increment. The resultant muzzle velocity for both is also same – 600m/s (at standard conditions -- average gun wear -- blah blah blah).

Firing BR-540 using Normal “Full” charge was strictly forbidden – old or new type charge construction.

I can only assume the inclusion of the "special" AP charge would have been to decrease turn over time in loading and firing AP. No need for increment removal. Time involved in putting accurately fired projectiles down range is obviously extremely critical in tank vs. tank gunnery.

 

[jeffduquette]

realism...now if we could only get the vehicles to run over/through trees...ouch ....cheap shot drive-by....

"Realism" is all relative and needs to be balanced with an enjoyable game experience. We want to have fun, but it's also nice to be able to get a feel for weapon systems and such and how these things act to shape or mold battlefield tactics. "Realism" would be me and you staring at a computer screen for 8-hours waiting for orders to advance than getting blown-up 2-minutes into an engagement by a hidden antitank gun. Fun stuff......lets play that scenario again.


Running through trees, fences and buildings would be fun -- but perhaps there should be the potential for immobilization associated with such activities; or the possibility of decapitating ones TC by running through wooded areas with low branches; or bogging down in muddy creek beds -- not to mention tanks simply throwing tracks or breaking this or that component while tearing up the battlefield at 25km/hr. Make the gamer change a track in the middle of the high California desert in the middle of August. That would be realistic...

It is humorous to listen to folks online whine and bleat about this or that aspect of what they perceive to be "realistic" and why the game or modded-game fall short of their particular take on what realism entails. I am of course often guilty of this sort of whinning myself . Mean time they (and me) are very content to merrily jump from driver’s seat to tank commander’s position with a simple key stroke. But we don't complain about that being "unrealistic". Or; by driving next to a stack of generic all flavor ammunition crates one gets an instant replenishment of their on board ammunition supply. But we don't complain about this being unrealistic. These are things that are probably best left alone given the game mechanics and the desire by the player to be entertained rather than be bludgeoned to death with "realism". There has to be a balance, and there is perhaps a fine line where that balance might be. Now if on the other hand a Tiger Tank does anything other than destroy all comers while shrugging off even the heaviest of shell fire, we are very inclined to complain about realism.

 

[mlespaul]

*nods in complete agreement* jeff, you speak the truth.

 

[[TW]Wilsonam]

*nods in complete agreement* jeff, you speak the truth.

LOL... he frequently does