# HSTV-L has an undeveloped ammo

(off-topic) where I can find this program to calculate?

Any numbers you get shouldn’t be taken as gospel. Your setting a reference distance. That would be a “Known Measurement” then it uses ratios to base off that known distance. Perspective plays a large part in it, so you need good photos of anything you want measured.

The only reason I don’t measure from the middle is because usually the perspective messes up and its hard to pinpoint the middle plateau where the case would be at its longest.

They shouldn’t be ignored, but we shouldn’t take any estimated numbers from them as facts.

My problem is, the 75mm AD gun is the shorter casing, we known due to the AD gun using a sliding breech mechanism that there were concerns. So they made a new gun, XM274. XM274 would use the rotating breech mechanism and use the longer case. The lengthened case being extended by 3". We know from sources that the 75mm MCAAAC problem only mentions having lengthen the case by 3 inches once, which was from switch to the XM274 from AD.

IF the 75mm AD gun original case was 400mm, then I can totally agree with XM274 cases being 483mm.

400mm = 15.75in

XM274 Gun
15.75 + 3" = 18.75" = 482.6mm (18.75 rounded up to 19")

These measurements for the cases make total sense for XM274 ammo to be 483mm

My issues is there’s to much cloudy sources and photos and can’t prove TO ME YET that XM274 is 483mm. But I don’t disagree that the estimated numbers we have for XM885 being 483mm makes total sense.

Assuming XM884 is 483mm due to not needing as much propellant cause its HE and it would take up more propellant volume in the case, reducing the amount of propellant used. Gives is near Delta 6 performance with correct Velocity used.

19x435mm @ In Game Velocity and Lowest stated source velocity of 1463 m/s

19x435mm @ Often stated 5300 f/s

19x435mm @ Found 5400 f/s source velocity

19x435mm @ Highest found source velocity of 5450 f/s

We are nearly approaching that 430mm stated performance of Delta 6

Some things I thought on overnight.

Do remember that M774 dimension are 26x345. Do we know if its mentioned anywhere that XM885 is longer then M774?

After re-looking at the Aberdeen photo you posted, those sabot petals are different from the Black 75mm Case photos.

There’s a lot of conflicting info for sure and I’m trying to make sense of it all. Maybe some more insights:

So regarding the 75 Advanced Development (AD), this is what it looks like according to the stoner tapes:

Spoiler

Now this does not look like a sliding breach design, rather a rotating breach just like XM274 (it just looks the same). Additionally, the drawing of the 75mm gun I provided earlier is actually that of the AD, for use on the HIMAG. I have found another drawing very similar to it that denotes it’s the 75mm AD and it clearly shows a rotating breach mechanism as well.

Spoiler

Now idk if it being the ADMAG makes it not an AD, I think it’s just an AD configured for the HIMAG however. The gun itself is probably the same as the AD.

This with the other ADMAG drawing with the round included, makes me believe the AD used the ~16" casing. And the ~420mm measurements are simply measuring errors with the left round being the one for the AD in that CTA collection picture, measuring probably around 16" irl. This is further reinforced by the actual irl measuring of that one 75mm round (color + lines on casing match) you posted also, measuring around 400-410mm (~16") in length. I do not believe that there is a round with actual ~420mm dimensions, it’s unlikely they made so many different sizes especially since this all would require redesigning the breach as well.

The shorter 75mm round on the right in the collection picture might have been the prototype round for an earlier 75mm gun with maybe that 26x270mm dart, perhaps the one with sliding breach too. That’s just speculation. But it’s like the only round of that length I’ve seen anywhere.

Then comes XM274, which would be the AD but with the breach lengthened to 19". I tried getting a picture of the round Stoner is holding with a bit less of a perspective and got this:

Spoiler

It’s likely that all rounds for the XM274 are black like for the 90mm, I have not seen any ones that have the black casing and be that ~16" length.

Another reason why I think the XM274 is 19" over the AD’s 16" (which is as shown before rotating breach as well) is the following quote:

Spoiler

Here it clearly says that the rotating chamber (breach) is what got lengthed, not a sliding one. Which seems to match the findings here that the AD shown above has a rotating breach and ~16" ammo casings (probably). Then again there might have been more AD’s during development.

But even without all this, that 19" round just exists, no question about it imo. Pixel measurements can be off but not by this much right? The fact Stoner pulls it out when talking about the XM274 breach that is in front makes me think that is correct. It’s otherwise hard to imagine where this number else is pulled from together with its association with XM274 in documents.

Now… I wonder if there is a way to contact ARES inc, probably not anymore?

iirc It was said on the old forum by someone or Spook that the 75mm AD was sliding or a earlier version of it was. There was a sliding breech 75mm at some point early on in the program.

I know for fact there is no 420mm case. 400mm is one of the 75mm case length. the 420mm come from estimations. Don’t fret of trying to find a shell casing thats 420mm.

100% Agree that there are two case lengths. 400mm and 483mm, no questions asked.

The confusion comes from trying to estimate case sizes in photos and the photos we have with those estimated lengths don’t entirely match up(To me). Of course pixel measurements can get close but shouldn’t be used to prove anything. They should only help reinforce evidence. Until either more information gets found or released I don’t think we will ever get a solid confirmation on XM885.

I couldn’t say. I would definitely want to visit Aberdeen to see if they still have that 105vs75mm APFSDS display.