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why is hstv-l has less pen then bulldog m41?
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I mean, on the website that the snails used to create this tank it says that it says penetration comparable to the M774 shell (372mm)
High Survivability Test Vehicle - Lightweight (HSTV-L) - Tank Encyclopedia
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It’s because the XM885 (Delta 3) dart is probably modeled quite wrong at the moment. Though, I’d like for anyone from Gaijin to provide the current sources on it to prove otherwise.
As of the (slightly outdated, but then again XM885 hasn’t changed one single bit since introduction) APFSDS stat spreadsheet, the XM885 is modelled as a 26x270mm APFSDS round with a muzzle velocity of 1463 m/s. M464 (the bulldog apfsds round) has roughly the same velocity, but the dart is modelled as a 20.6x309mm round, which gives it improved penetration because of length.
We know from documents that the muzzle velocity is already incorrect for the gun used on the HSTV-L. It should be more around 1600 m/s. Not to mention the dimension of the dart make not a whole lot of sense. It’s really not consistent how Gaijin models some APFSDS, take for instance OFL 90 F1 APFSDS and XM885. Very similar weight and they are both modelled with the same subcaliber diameter, yet somehow the 90mm APFSDS is able to be 105mm longer than XM885. That kinda makes no sense, if we assume these rods are modelled as cylinders, that just exceeds its actual weight.
I’ve been trying to find more info on XM885 lately, but it’s really hard to find any. This is all I can really find, that is somewhat conclusive.
Cartridge case (from “The Eugene Stoner Tapes - Part 7: Large Caliber Cannons”):
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Cartridge case with dart:
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Dart with sabot:
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XM885 (100% it) dart on display (XM884 HEVT as well):
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Doing pixel measurements on the last image, with the game given diameter of 26mm, gives a length of 570+mm, which is completely absurd and not possible.
I measured around 375 pixels for length (I only included the length were the diameter is constant, so excluding tip) and 17 pixels for width. Trying to keep this ratio, together with a mass of m = 2.27 kg (mass according to docs) and density of 18600 (density used by WT for DU, which it is according to docs, in game it’s WA). Results are about a 19x420mm dart, which makes more sense considering it is a CTA round, which often use near the entire length of the case (case dimensions are 5.2x19" according to docs).
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Putting it through Lanz Odermatt gives 364.3mm@0° which matches M774 stats quite well as well as documents. However with corrected velocity for XM885 of 1646 m/s, penetration increases to 399.9mm@0°. Which matches the description of the page you linked.
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Sadly of course this is not enough evidence for Gaijin to fix XM885, however I hope it is able to at least prompt Gaijin to revisit the 75mm XM274. Becaues the current statistics are even more nonesense and most likely based on nothing. And I’d also still like to see XM884 for the gun, but that’s besides the point.
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Thats really cool information, thanks. But btw, why the snails dont wanna up penetration xm885? Cus if hstv-l been on 9.7 (like 4 years ago) its been okay, but on top tier that ammo cant penetrate t80 bvm and t72b3 in side and leo 2 in front.
Probably a mix of balance and lack of information. Balance is really up to Gaijin only sadly, there’s not much to say about that. I hope Gaijin will eventually at least try reestimate XM885, because again, the current stats are nonesense.
I would also fully accept the HSTV-L moving to 11.7, if XM885 got fixed (and maybe even with addition of XM884?).
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It’s good to see Gaijin at least acknowledge the ammunition issue.
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I’ve been research XM274 out of curiosity given XM885 history with Spookston and others.
My only problem with my research is im finding problems with XM885 length. Multiple Sources state 5.2x19" / 132x483mm yet theres evidence of 132x400mm.
For the 5.2x19" it’s also not sure if it’s XM885 either, might not be. I think the document where that comes from states just 75mm ARES or something like that, not very specific. I guess the only way to get conclusive info is getting it from a someone who worked on it. But it might still be classified to the company itself.
All we know is for sure the pen right now is just completely wrong, in game pen is just not nearly M774 like penetration, and Delta 6 was stated to have ~430mm penetration, which just means you can definitely get a LOT of performance out of a 75mm gun, which Gaijin seems to not acknowledge. Though I guess Gaijin has a hard time trusting the word of the people who developed it.
Pardon this wall of copium. Please pick it apart, I would love to hear were I made errors.
I was able to find two different mentions of 5.2/19" dimensions yet, all photos nearly disprove the 19" case length.
DoD CTA Program Report No. 96-164
I can’t recall where I got this photo. Maybe old Forum?
Two things can be confirmed from these two documents alone:
- Both confirm case dimension of 5.2x19" (Measurements in second photo align with our case dimensions)
- Case mass being 12.7 kg
- This is one of 1463 m/s Velocity sources Gaijin uses.
- 3 kg projectile or am I misunderstanding launch mass?
The problem with the 5.2x19" is that there isn’t any photographic evidence that supports this.
The Counter Source for there 19" Cases are these HE INERT photos:
Theses measurements put the case dimensions at 5.2x16" 132/~400mm
While these photos aren’t of XM885, we can use the Heat Transfer and Erosion Testing Document to find a cross-section of the slugs used which look similar to previous images:
Next, is the ARES family photo. You can watch the Stoner Tapes Part 7 where they explicitly
state which shell is which.
- We know the XM274 was lengthened by 3" for increase performance. The family photos validates this.
- Using the 35mm Oerlikon projectile, we can ESTIMATE the size of these.
This puts XM274 cases at roughly 132x420mm which is nearly identical to the HE INERT photos in measurements. All of the measurements in the above photo match with what they should be. Black 90mm case has a 90mm bore hole. If we take the original stated 483mm length and measure everything off that, the measurements don’t align with what we know they should be.
35mm Shell being 38mm in width? Wrong.
90mm Bore width at 102mm? Wrong.
132mm XM274 width? 10mm over.
The expected measurements are too far off with using 483mm. Whereas measuring with 35mm shell, all the measurements align almost perfectly.
The final photos being Black 75mm Sabot Photos:
Unfortunately, we can’t really use measurement here due to the perspective BUT what these photos do provide is what XM885 dart looks like. Which looks identical to XM885 in this photo:
The fins in both photos look identical in design so we can safely agree that there are two good photos of XM885.
Lastly, find the estimated length of XM885 from the above picture. We have pictures that disprove the 483mm length. so XM274 cases are in the range of 400mm in length. We know due to design of CTA ammunition that APFSDS don’t take up the full length of the projectile. The primer need reinforcing material and the Dart itself needs some powder behind it. So XM885 can’t be 400mm (Unless the cases are longer then 400mm).
Assuming given the U.S Army and Marines wanted as much performance out of XM885 as possible its reasonable to believe the Dart we be AS LONG AS POSSIBLE. Where as with XM884 (HE) where velocity is less important, we can also come to believe that XM884 would be longer if only slightly then XM885, nearly taking up the entire 400-420mm length.
Assuming XM884 is 420mm
XM885 at most is 380mm. That gives 20mm for primer material and propellant to be directly behind the dart which is reasonable given that smaller CTA case cross-section agrees with this:
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26x270mm
19x380mm @ 1463 m/s
19x380mm @ 1661 m/s (This is highest velocity that can be found in sources)
19x380mm @ 1661 m/s puts us near M774 performance.
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Funny story, if you wanna dig through the old forum to find spookston’s old bug report on the length of the round, a gaijin dev went and literally replied to his post about the length of the ammo with “we don’t believe this is true”.
Some points I wanted to comment on (not criticism, just trying to think with you):
This is probably dart + sabot weight.
That’s correct. I have thought about this as well. I know for a fact at least that there were 75mm APFSDS rounds for the gun before XM885, which were shorter. The rounds here however might be from earlier prototypes and not XM885 however. It’s hard to say because it does not list them by name.
And then we have the casing Stoner himself presents in the interview:
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Which, using pixel measurements seem to not fit the 420mm case length. It in fact lines up pretty well with the 483mm figure (I wasn’t very precise in my pixel measurment, so please confirm, it seems tho that a 420mm length is unlikely here). I am convinced this is XM885, I hadn’t found the second picture you had but now I am very much convinced. I think it’s from Janes, looks like it. I have a theory, if you can call it that, that later 75mm rounds had the black casing whereas the earlier pre-XM885 rounds were of that beige color (420mm length casing). The photo of all the casings together might just be an older photo in that case.
Another photo I found may also show what may have been the prototype round before XM885, that Gaijin might have based the current dart stats on (and might also have used the 420mm length casing):
This one is a muuuch wider dart with a much lower L/D ratio. 26mm dart width seems plausible and so is the 270mm dart length here. But this dart is most definitely NOT XM885. As the picture you and I provided with the labeled XM885 dart has a different fin structure and a much higher L/D ratio.
And of course another thing Gaijin did wrong is the material of the dart. Though not as large of a problem, currently XM885 in game is modelled with the density of WA and not DU. Even though sources for XM885 have stated it is DU. At least in the last major update XM885 got its missing 70g of mass…
Lastly, I must admit my estimate is probably overestimating the dart length by quite a bit. I didn’t account for fin weight, tracer weight, etc. Neither did I probably accurately measure the photo. I think a L/D of 20 is probably around the right number, but that’s just speculation. And the margin for error can be quite large with low resolution pictures. All in all though, by a large margin it shows that the current in game stats are wrong. All we can really hope for, unless we have documents stating the dart length, is that Gaijin themselves reevaluates the dart dimensions again to at least fit to the “similar to M774” performance.
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That makes much more sense.
When I started researching XM274 and XM885, I thought initially any Black Case were 90mm rounds and I was trying to back measure down to the older biege/yellow rounds. It wasn’t until I went and watched old Spookston videos and Stoner Tapes where they (Stoner Himself?) explicitly said that black cases were 90mm. Given the Black 75mm case photo exists, I made the assumption that black/yellow can’t be used to tell which caliber the case is. So my current thought is that black is more production case where yellow is early prototype of material.
Heres your photo based on 483mm length
Same photo based on 132mm width
Its in between both of our measurements. Hard to measure my way given the perspective so my numbers are just simply estimate.
Its highly probable that this photo is of 75mm AD XM885. I can see this picture being the one Gaijin based in-game XM885 on.
Its worth mentioning but the sabot petals do look identical. Can say 100% certain that XM885 regardless of which size it is has 4 sabot petals
While im not sure how far XM885 sits down inside the casing but if it sits flush with the rim, this gives a good estimate.
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Assuming XM885 sabot and the Erosion testing Slugs follow same sealing rings dimension.
This picture I get the sealing ring at ~15mm.
This image I get ~13mm
There have been hundred of post about this and even Spookston make like 3 vids about it and a very detailed post on the old forum but gaijin just don’t cares.
At least they acknowledged it now so maybe expect a fix in 2 more years.
It is because most of the reports are made in forums which isn’t right, when doing this you guys could use Gaijin Issues support.
Except there are alr a bunch of report about this if you actually search it up with some dating back as far as 2 yrs ago. Have you even bother checking?
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The pixel measuring, although very likely disproving the current in game values, are not accepted by Gaijin. I can understand that considering the margin of error being very high especially on lower resolution pictures.
All the documentation that could be of use has already been reported to Gaijin and should be known to them already.
Now in many cases you cannot break tank from a side, so 270mm pen is much to low for 11.3 BR.
I think due to perspective it’s much fairer to measure the diameter by taking the middle thickness, and it’s important to take into account that the top of the round (or actually bottom rather) is curved, so the top is slightly higher than the rim. I don’t want to declare this as valid, but it can line up:
I also went ahead and quickly made a 3D cylinder overlap it to show the comparison between a 483mm (yellow) and 420mm (green) case:
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It’s not perfect either but the 483mm one can fit it more or less, do keep in mind the actual round is not a perfect cylinder as it has that rounded top and the 420mm doesn’t fit. So what I think personally is that the shorter beige round is indeed a prototype round (perhaps even one that fitted the 26x270mm apfsds round) and the black round is the XM885 which is 5.2x19". I am just very convinced the 483mm case is XM885 especially since we have actual documentated numbers for it.
Even then, maybe we should ignore all rounds that have some perspective to them as there may be rounding errors. This picture shows a drawing of 105 and the 75mm rounds:
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Which gives a different length… once again! Such fun. Anyways, given this length and the much more accurate length probably (if the drawing is to be trusted) a 3 inch difference to Delta 3 (XM885) would put it in the ballpark of a near exact 483mm, or 19" long casing. Which matches documentation and these black rounds (at least from my measuring).
I am therefore inclined to believe Delta 3, or XM885 probably is 19" long for the casing. Spookston’s tank ency article also worded it so that the pervious round (probably this 16" ~407mm, or 420mm(?) by your measurement) had M774 performance. Which according to your found stats seems to match perfectly. But then he goes on to say the breach was lengthened by 3 inches (which probably means indeed a 3 inch longer casing) which was to accomodate for the Delta 3 (XM885) round (so probably the 19" casing).
Then there is also Delta 6 with 430mm penetration. Idk if this may have used that 19" casing as well, maybe not. But it was tested apparently, however I’m not sure if they again lengthened the gun breach or tested it out of some test setup gun. But a 19" case would also be able to accomodate for it possibly, which would mean no extra breach modifications had to be made from the Delta 3 initiative. But idk, this is just me thinking out loud.
What do you think? Hard to find much more. I think having a good overview of all the rounds the 75mm gun had would be a good start. So we have at least that very short prototype one (probably housing the 26x270mm dart), the initial round for the XM274 (either it is that 407mm one or 420mm, or they are different) and then we have Delta 3 (XM885) and Delta 6. Unless you believe that the 420mm casing you measured is Delta 3, though it would make the documentated length and that Janes’ picture (listed as XM885) as well as possibly the round Stoner is holding an anomaly. I do not believe them to be Delta 6, unless you have other ideas.
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Now that I see it again, yeah the drawing dimensions seem to line up with the HE round as well. Which is roughly 16", again 3 inch shorter than the 19" round that is what I think XM885. The 420mm might just be an error due to perspective or something else that I do not know of.