The PERFECT WAR Mod : Guns

[JWE]

ORIGINAL: JuanG
So I'm not sure where we seem to be falling out of sync. One thing you said caught my attention though; you said your data was all at best case strike angle; I hope this does not mean you are disregarding angle of fall?

No, Sir. Strike angle is the angle at which a shell will impact a target, along a ballistic trajectory. Angle of fall, all that stuff. Only using vertical obliquity, no yaw, no twist, no tumble, just simple orthogonal ballistics trig.

For the raw ballistics, I use Interleave Systems v104. Math is the same as Nathan's, so just normalize to reported values. All that's of interest is striking angle and striking velocity, anyway. And it's all normalized. [;)][;)]

[JuanG]

ORIGINAL: JWE

ORIGINAL: JuanG
So I'm not sure where we seem to be falling out of sync. One thing you said caught my attention though; you said your data was all at best case strike angle; I hope this does not mean you are disregarding angle of fall?

No, Sir. Strike angle is the angle at which a shell will impact a target, along a ballistic trajectory. Angle of fall, all that stuff. Only using vertical obliquity, no yaw, no twist, no tumble, just simple orthogonal ballistics trig.

Figured it would be something like that, so I apologise for even asking. Was just grasping at straws hoping to find where things go wrong. Right now I can only assume were working to entirely different calculated limits for the weapons, but even that should only shift our results in one direction or the other; we seem to be getting different trends entirely for some of them.

ORIGINAL: JWE

For the raw ballistics, I use Interleave Systems v104. Math is the same as Nathan's, so just normalize to reported values. All that's of interest is striking angle and striking velocity, anyway. And it's all normalized. [;)][;)]

I use NAaBs ballistics model which is based on Robert McCoys work, backed up by BigGun from Rick Robinson (particularly for non-historic weapons), and check this all against secondary data where possible. Generally NAaBs model is within 1-2% of secondary data, and can be corrected where needed. Would be interested in hearing more about this program you use as I've never come across it, despite scouring the internet for ballistics programs.

[FatR]

I just want to say that I'm wathching the discussion with interest... Thanks, Juan and John.

[JWE]

Hi Juan, Interleave isn't a specific ballistics program, it's a full boogie math analysis program. Costs a butt load, but we have a small-site license, so I can play with it.

Input the complete (as I can get them) ballistics equations, including all the drag and dynamic motion crap. Then set everything I could rationally justify to '1':
No vertical displacement - gun and target on same plane
No horizontal deflection - target axis is 90 degrees to gun azimuth
.. no pitch motion; gun and target are stationary
.. no track motion; gun orthogonal and target axis are parallel
Standard meteorology - Nav OP standard conditions
.. ignored altitude function of atmospheric density
.. no wind
Standard trajectory of shell axis - tangent to calculated trajectory
.. no yaw, pitch, skew (might give +/- 5 degrees to SA), assumes direct tangent
Standard ballistics coefficient
.. nominal except 'form factor' (i) which is extracted from G5 body type and normalized to 1
.. bourelette diameter set to nominal shell diameter

That pretty much seems to be the booger. So ran it and plotted the results against the published range tables in Nav-OP 1237, 830, 807, 243, et seq. Did a curve fit with K' as the fitting parameter, and went for a four point fit, at 0k, 10k, 20k, 30k yds, and lo and behold, with a K' of 1.31, I get a curve match with a maximum of 1.3% offset for any calculated data point. And that ain't bad. Especially considering the Navy used an emperical K' in constructing the tables anyway. Because they couldn't do the complex atmospheric math either, so they went empirical and extracted a K' value. Go figure. Woof !!

Sending you the data tables: Actual OP-Nav numbers compared to calculated JPr numbers from 0 to 26k-32k, in 2k increments. Giving the K' numbers, the bourelette diameters, ogive diameters, crh calcs, shell and body weights, and bears, oh my!

Ciao. John

[PaxMondo]

ORIGINAL: JWE

Hi Juan, Interleave isn't a specific ballistics program, it's a full boogie math analysis program. Costs a butt load, but we have a small-site license, so I can play with it.

Now, that's what I call a nice perk.

[&o][&o][&o]

[el cid again]

Teacher - teacher - I object!

There are advantages and disadvantages to different national technologies. If you pick your argument carefully - well - one might come to
quite different conclusions.

While I am not quite a JFB - my Navy chief was right when he alleged "Japan had better warships." That wasn't entirely a matter of gunnery,
nor the technical specs of the guns - but there are cases where it was.

There is universal consensus, internationally, that the best Japanese gun was the 10 cm (3.9 inch 65) Type 98. Used on AA destroyers and in more than 110 mountings ashore, it was a superb weapon, for which there is nothing comparable in the US at all. It is a fine weapon in terms of ballistic performance - weight of shell - ROF - range - etc. But much more - also in terms of rate of elevation and traverse of the mountings, and in terms of the fire control system - which was almost unique in Japan. But there is still more - Japanese naval AAA was supported ashore by what, today, we would call "simulator" training - for which we had no comparison. While the Japanese did not permit AA gunners to fire live ammunition - they had much less need to do that than we did - since they could train in the simulators. These used actual directors, actual fire control computers, and scale models of target aircraft "flying" on wires - inside something like a planetarioum which could simulate all lighting conditions. So - wether one takes the weapon purely as a gun - or as a weapon system - it was absolutely fine. The AA destroyers - with four twin mountings - were able to outrange and put more weight of metal on a traditional destroyer - and in simulation, at least - you don't want to have to face one.

There is a lesser case, far less well known. This weapon is actually related, designed at the same time, as a pure AA mounting - and it is comparable really only to a post war US 3 inch 50 - the kind I served with 20 years later - better than similar sounding wartime and pre-war 3 inch 50s. But the Japanese had it operational during the war. This is the 76 mm (3 inch 60) Type 98. It used the same fire control system as the 4 inch described above. It was, however, not widely made - serving in a light cruiser class and in four twin mountings ashore at Maizuru. But IF the Japanese had produced it instead of older 3 inch guns - it would have changed the game. It replaces the need for medium AAA - not just is superb heavy AAA.

Other cases of superior Japanese guns exist. The Japanese had a late war 5 inch comparable to a US 5 inch 54 - except the US model - I served with it as well - NEVER was successful. But the Japanese perfected the weapon in 1945 - not a bad achievement in the conditions.

On land, the IJN fielded something almost wholly unknown. Japanese naval 8 inch guns were adapted into single mountings for AAA use - so were 6 inch - and the 8 inch was wholly unknown for 60 years - except insofar as it was the basis for orders that B-29s not attack Singapore (we were not entirely sure what the weapons was?). The battery was found a few years ago - in a park - covered with foliage. Remarkably, the mountings look for all the world like the 155 mounting intended for modern US destroyers and, sometimes, for support ships - a very sleek, streamlined - and light weight - mounting. There was also an Army 149.1 mm weapon fielded only to defend the Imperial Palace - but it was only of marginal performance - particularly in elevation and traverse. The 8 inch - as the 5 inch - and the 4 and 3 inch described above - wes without peer - in that era. Only decades later did the French field a somewhat similar 100 mm - we never have done - and as I noted - our post war 3 inch 50 was at least in the same league. But for 1938 designs? Remarkable work.

So - "forget the whole thing" is complely unfair and misleading.

ORIGINAL: JWE

Didn't think it right to step on the main thread for this, so opened another for gunbunnys everywhere. Lest I be accused of being a fanboi for one side or t'other, here's the US 6"/47 shooting the Mk-35 and 8"/55 shooting the Mk-19 and Mk-21 plotted (blue) over the corresponding Japanese guns.

The 6 inch gun specs are wicked close. US 8 inch gun specs are significantly better. Read shell steel for them. For 6 inchers, it gets down to RoF, and dispersion. The US guns had 4x the former and 1/2 the latter. Even at the end of the war, Japan could never come close to even the Mk-4 of the 1936 Brooklyns, in any way, shape, or form. Sigh ... what a sad day for JFBs. Japanese gun technology sucked so bad (when viewed realistically) it might be worthwhile forgetting about it.

Ciao. [8D]

[JuanG]

ORIGINAL: JWE

Hi Juan, Interleave isn't a specific ballistics program, it's a full boogie math analysis program. Costs a butt load, but we have a small-site license, so I can play with it.

Handy. Probably would have had access to something similar at University, but unfortunately that opportunity is gone.

Regardless, I think its clear that theres some differences were getting on our ballistic data, as well as possibly using a different standard to measure against.

I propose we both post the ballistic data for the IJN 6.1"/60 and the US 6"/47 and see where our results differ, and compare them to the real figures.

[JWE]

ORIGINAL: JuanG
Regardless, I think its clear that theres some differences were getting on our ballistic data, as well as possibly using a different standard to measure against.

Think so, too. Might have found at least one source of discontinuity. Ran NaAB and found few significant differences in the 6", Mk-36, between NaAB model and mine/Nathans. Striking angle/velocity were all ok. My form factor was a skoosk different, but when I tweaked the NaAB model with a (slightly) different ballistics coefficient, it came in, perfect, for angle and velocity as a function of range/elevation. Pen still bit the Willy, so wtfo?

Then, the light dawned. NaAB uses the standard Mk-36, Mod 1-?, with 106.9 lb body wt. It shows the parameters, but one can't modify them. Hope to gosh that I was specific enough, somewhere, to say I was plotting the Mk-35, Mod 9, with 100.2 lb body wt. This dude penetrates better then the earlier shell. The earlier shell penetration numbers agree reasonably well between FACEHARD and NaAB, but NaAB can only run its standard shell set. One cannot tweak shell parameters in NaAB ... sigh ...
[am furiously adding the nominal and the differences to the the data set. Think I see just where we agree, and where/why we do not]

I propose we both post the ballistic data for the IJN 6.1"/60 and the US 6"/47 and see where our results differ, and compare them to the real figures.

Yeah, let's definitely do that. I haven't had this much fun since I ran into the Le Petomaine thruway and had to go back home to get a $hitload of dimes (Mel Brooks joke). Seriously, let's do that.

Ciao. John

[JuanG]

ORIGINAL: JWE

ORIGINAL: JuanG
Regardless, I think its clear that theres some differences were getting on our ballistic data, as well as possibly using a different standard to measure against.

Think so, too. Might have found at least one source of discontinuity. Ran NaAB and found few significant differences in the 6", Mk-36, between NaAB model and mine/Nathans. Striking angle/velocity were all ok. My form factor was a skoosk different, but when I tweaked the NaAB model with a (slightly) different ballistics coefficient, it came in, perfect, for angle and velocity as a function of range/elevation. Pen still bit the Willy, so wtfo?

Then, the light dawned. NaAB uses the standard Mk-36, Mod 1-?, with 106.9 lb body wt. It shows the parameters, but one can't modify them. Hope to gosh that I was specific enough, somewhere, to say I was plotting the Mk-35, Mod 9, with 100.2 lb body wt. This dude penetrates better then the earlier shell. The earlier shell penetration numbers agree reasonably well between FACEHARD and NaAB, but NaAB can only run its standard shell set. One cannot tweak shell parameters in NaAB ... sigh ...
[am furiously adding the nominal and the differences to the the data set. Think I see just where we agree, and where/why we do not]

The Mod9 thru Mod11 with 100.2lbs body, introduced in 1944 is available in NAaB too, 3 lines below the earlier Mod1 thru Mod8 shell used for the early years. Slightly misguiding as the line starts with 3", but its right there. I plotted it on my first curve too. [;)]

I get exactly the same numbers out of NAaB as I do out of facehard for that shell.

Will get you a table of 6.1" ballistics at 5.5kyds intervals, and a 6" table at 6k, 10k, 16k, etc later tonight.

[JWE]

You are a Prince, Juan. Thank you.

[JuanG]

Here you go; the values I used from NAaB (note im not using quite the stock BC values, as I find these are a slightly better fit), along with their associated penetrations, and then NavWeaps ballistics along with calculated data for them. Im trying to dig up a table of 6"/47 penetration values I've seen somewhere, but I cant remember where off hand.

The biggest differences between NAaBs model and the real data is regarding angle of fall, but even then the penetration values generally work out to rather close. And of course, where needed they can be adjusted.



EDIT: The BC for the 6"/47 is missing for whatever reason. I used 6.72.

In general, Ive found NAaB to be a great tool to work with because it is (barring the strange arrangement of some of the projectile data) much easier to work with than FaceHard, especially since I'm on a 64-bit machine and that means FaceHard needs an emulator to run.

Regards,
Juan

[JWE]

NaAB is indeed an excellent tool. Must say the FACEHARD interface is a pain in the tush. [;)] Ok, top of the pic is VS and Obliquity got from the Range Charts in Nav OP 830. Middle is from my calcs, last is from NaAB. They are in pretty good agreement.

Pen values for the middle set are what I got before and what's on that plot I did. Pen values for NaAB are from (surprise, surprise) NaAB. Good bit of difference at first. Then found the Mod-9 shell where you suggested I look and, lo and behold! Finally got NaAB values similar to the ones I got. Yay !!

So it doesn't look like there's much (if any) difference between what we are both getting for the 6"/47 shooting the Mk 35 M-9. Also showing the FaceHD68 output, so you can see the input parameters. The NaAB input parameters were identical.

Now, we need to get after those pesky Japanese guns.

[JWE]

Ok, then did the 6.1"/60. Ran the numbers against ordinary everyday 1937 vintage Class A, with FaceHD68, just like before, and got the same numbers as before. Then ran the numbers with NaAB, against ordinary everyday 1937 vintage Class A, and got penetration values considerably "less" than mine. Woof!!, says I. What the hey, Batman? (btw, "everything" is at N1-Eff NL, FaceHD68; Full Pen, NaAB. They are equivalent.)

Then I went to my trusty Lacroix & Wells, page 462, Table 9-7 and got some published numbers. They say 108mm at 15km and 100mm at 10km. No way I believe 4 inches at 22k yds, but 4.2 inches at 16k yds doesn't sound too bad. Then noticed the pen value was against NVNC, so I shot the little swine against some New Vickers with NaAB. It was a quickie, so I only got a few values, but enough, I think. Better, but still no cigar with respect to L&W. So then I shot the little swine against some New Vickers with FaceHD68, and got values that come much closer to the L&W values.

So, comparing apples, to apples, to apples, it looks like the values I plotted originally are pretty darn good, if not more complimentary to the Japanese 6.1/60. If I plotted the NaAB values, the penetrations would fall much farther below the 6"/47 than I show in the plot.

It's very hard to verify models without real world data, and there isn't a whole bunch of that for the 6.1"/60. But I am heartened that my ballistics output and FaceHD68 give the best agreement with what little there is available. I did find what I might consider a technical blivet in the NaAB program, for this gun. The program gives a BC of 5.33. The shell has a sectional density of 3.31, which suggests a form coefficient of 1.62, but this value is in the G5 realm (boat tail, 6crh, tangent). A better form coefficient might be from 1.8 to 1.9, in the G6 realm (flat base, 6crh, secant). That would give the little swine a BC of between 5.96 and 6.29. But then, NaAB calculates everything on a single drag model. If you click between the G5 and G6 drag plots (in NaAB), you'll see exactly why and how I got the better striking angles and velocities (and thus, penetration) for the Japanese gun.

Woof !! This is so cool !! Thanks for digging deep, Juan !! Looking forward to hearing more.

[JuanG]

Everything you've posted looks good and agrees with what I've got, except for the values you got out of NAaB for the US Shells, which were too high. Tried to figure out what was wrong and where, and came to the conclusion that you tested them both against Japanese armour, which, if I follow it to its logical conclusion, means that the curves you posted originally had the 6"/47 vs Japanese armour (JVH, or JNVNC, no major differences), and the 6.1"/60 against US Class A.

Surely, if were trying to find out which was the better weapon, ballistically, then we need to test them against the same standard ('dont change more than 1 variable in a controlled experiment, etc, etc' Science 101 - in this case the shell/gun system)? This can be either Class A or something else, but please do let people know if you plot data against different standards, on the same graph no less.

Regarding BC, you'll notice I used a slightly higher one, as I came to the same conclusion. Its a shame NAaBs drag model is a little simple, but I suppose it works well enough for most things.

[chesmart]

Lovely gun geeky post I am enjoying it and learning at the same time

[JWE]

ORIGINAL: JuanG
but please do let people know if you plot data against different standards, on the same graph no less.

You are absolutely right. I probably spent too much time noting that the J gun curves were against US Class-A and Brit HCA armor and not enough noting that A gun curves were against Japanese NVNC armor. Acknowledge my fault.

I wasn't actually trying to say which was technically the best ballistics performer, just looking at performance in practice; thus, Allied guns shoot at Japanese ships, and Japanese guns shoot at Allied ships. My rationale is that I have been spending time translating technical performance parameters into game terms, so that has become my general context. I will do my best to make it more clear, in future, especially if you are looking at it, Juan [;)]

Ciao. John

[Whisper]

And now you are beating yourself with mea culpa, maybe you can publish the accuracy specs we've been waiting a month for! Skipper! Dork!

Jeremy