Vanir Ausf B

Sure looks to me like they both have a ballistic cap.

It's much better now. It's still possible to get them but it seems to only happen with really huge games. I haven't had even one since the patch. I play on a 3 year old laptop with 4 GB of RAM and 1 GB of VRAM.

Keep in mind that the Tiger is RHA.

It seems to be in the ballpark. You can always quibble a little here or there because every source you find will give different numbers to a greater or lesser degree. But Rexford's figures and the US July 1944 field manual data are pretty close to each other and they seem to match what people are observing in their game tests, generally. I think a case could be made for increasing the Pz IV front armor plate thicknesses by a couple of millimeters. Rexford's book suggests up to 5mm variation in thickness of those plates, which the books says are based on actual measurements. This 1943 US diagram of a Pz IV G labels the glacis plate as 22mm thick, an oddball figure unlikely to have been arrived at by means other than measuring an example.

... at 1000 meters

Yes, my own Google-fu had turned up all of those except the last link, which is interesting since it confirms that both M61 and M61a1 are ballistic capped.

I need to clarify a few things. I agree. You're welcome. This was a working theory I had earlier in the thread, but I've change my thinking. As I said in my last post, I think what a few sources have been calling the "M62" was actually an improved version of the M61: the M61a1. As akd pointed out, the real M62 was a 76mm round. When the M61a1 was introduced I do not know, but official US documents and tests during the summer of '44 strongly suggest it was the main US 75mm armor piercing round in service in the ETO by D-Day, so it almost had to have been present since at least early 1944 and maybe sometime in 1943. So it looks to me that CMBN is correct to use M61a1 aka "M62". Whether or not it is appropriate for CMFI is an open question. I wouldn't assume anything without more information on introduction date.

July 1944 field manual FM 17-12 Tank Gunnery Those ranges are in yards. Multiplied by 1.27 to convert to 0° we get penetration of: 500m: 100mm 1000m: 90mm 1500m: 80.6mm WO 185/178, 1943 (don't know the month) They Brits are nice enough to convert to 0° for us. Unfortunately the ranges are in yards so the numbers in meters would be a bit lower. 500y = 457m 1000y = 914m 1500y = 1372m Rexford's book lists US APCBC penetration against FHA @ 0° as: 500m: 95mm 1000m: 86mm 1500: 79mm These figures are very slightly lower than the US official July 1944 numbers listed above at 500 and 1000m, but nearly identical at 1500m. Note the maximum range for Pz IV "upper hull front" vulnerability as 1470 yards which equals 1344 meters. This seems more pessimistic than the FM 17-12 numbers, but we are not given penetration numbers here to compare and they don't define vulnerability. Interestingly it also references APC projectile M61a1. I Googled this and got very little but the Wiki entry for the Sherman 75mm gun states This makes me suspect that the 75mm "M62" shell is actually a mislabeled M61a1.

For the 57mm gun APCBC Rexford's book give a value of 91mm penetration at 0°

Hey John, we are having a little discussion about this over at the CMFI forum. The question of when M62 became available has come up since it represents a very significant performance increase over M61 against the Pz IV. Armor penetration tests and tables from 1943 and 1944 (at least through the Isginy tests in July '44) do not list M62. In fact, I'm not sure what the exact difference is between M62 and M61.

Ok, I think I see what you mean. I dug around and found a formula for the exact slope modifier at 30° for the specific T/Ds we are using. The formula is: a x (T/D)ⁿ where a=1.2667 and n=.0655. Applying this to 75mm attacking 20mm thick armor we get a slope modifier of 1.16. So applying that to the numbers on Taffif.net we get M62 penetration of 79mm at 1000m and 71mm at 1500m. With M61 ammo we get 67mm at 1000m and 57mm at 1500. Against the 80mm thick driver plate we have a modifier of 1.27 which gives us 77.5mm of penetration at 1500m for M62 and 62mm with M61 ammo. Obviosly the question of M62 ammo is huge since it allows penetration of the Pz IV front hull at ranges of about 500m or more further than does M61.

Bad info deleted

Yes, there was also a M62 76mm round. This is all very curious. Lone Sentry has penetration tables from the July 1944 field manual FM 17-12 Tank Gunnery. The 76mm M62 is listed for the 76mm, but only the M61 and M72 are mentioned for 75mm, with only M61 is present on the penetration tables. Results from the the Shoeburyness tests conducted in May of 1944 are reproduced here and also do not list a M62 round for the 75mm. A little further down on the same page results for the Isigny live fire tests in July of 1944 again only lists the M61 round for the 75mm. Over on the CMBN board John Waters, who knows far more about this stuff than I do, wrote : So it seems that the M62 round was a late war modification to existing M72 rounds that would not have existed during the CMFI time frame and possibly not during the CMBN time frame.

Slope modifier is a function of T/D, but T/D for 30° is exactly the same as 0° since neither the actual armor thickness nor shell diameter change. I'll have to look at my stuff tomorrow to double check but I've been using that conversion for a while and it always seems to work out correctly. siffo may be on to something regarding the ammo. Most penetration tables I've looked at only list M61 and M72. I don't know when M62 was issued or in what quantities. Need more information.

I'm pretty sure that is not true since T/D is calculated using actual thickness -- which is the same at every angle -- rather than equivalent thickness.

To convert 30° data to 0° you multiply by 1.22 (IIRC). I don't know. Should it?

Depends on ammunition. This would be true using uncapped M72 AP, which performs similarly to Soviet BR-350a (which also does not have a penetrative cap), but capped ammunition is a different story. http://www.tarrif.net/cgi/production/all_vehicles_adv.php?op=getvehicles&vehiclesX=197

World War II Ballistics: Armor and Gunnery by Lorrin "Rexford" Bird and Robert D. Livingston

Soviet BR-350a fired at 612 m/s penetrates 61mm of FHA at 700m. Fired at 655 m/s it penetrates 68mm @ 700m.

Keep in mind that the numbers from the book I referenced are not necessarily the minimums. The authors don't say where they got the numbers from, unfortunately. It's possible those are measurements of actual tanks. That same book also gives a thickness of 85mm for the driver plate and upper nose which is almost certainly not the minimum spec given that every other source lists 80mm. Different versions of the Sherman have different hull thicknesses and slope. They also vary by armor quality. Some Shermans had cast armor hulls that should be weaker than the welded hull versions. You can tell which are cast by the rounded edges. Also, try testing the IV J at 1000m. It should win.

OK, I see what you mean. The Pz IV in the Lone Sentry diagram is a Ausf F2 or early G, which my source has with a 25mm glacis plate. So right now we have different sources giving different values. But with the differences being only a few millimeters it's possible there could have been variation in vehicles made by different factories or manufacturers.

I'm not seeing a Pz IV with a 50mm thick glacis plate on that page. Are you sure you're not looking at the Pz III?

That is the T/D (thickness/diameter) ratio and it's factored onto the penetration figures.

It's fairly smooth for me and I haven't noticed any delay. I play on a 3 year old laptop. Recently? Thief 2, Civ IV and Fallout 1.

:confused: That's exactly how it works in CMBN.