Sherman Tank Myths - Bad facts and Analysis of the 75s and 76mmBy Copyright 2015, J.D. Neal, All Rights Reserved

The author wrote of confusion caused by what seemed like misleading lengths of the 75-mm and 76-mm complete rounds and projectiles in Artillery Ammunition TM9-1901 June 1944. Here is a second case where poor numbers have caused me grief - which I only realized a few days ago in June 2015.

75-mm M2 versus 75-mm M3 Tank Gun Muzzle Velocity

Before I had access to any sort of rigorous numbers I scrounged for data as best I could. I wanted to know what the shot weights and velocities of all the cannon were. Information on the 75-mm M2 and M3 was misleading.

The Illustrated Directory of Tanks of The World by David Miller (Salamander; 2000) gave the velocity of the M2 as 1850 feet per second (f/s) and the M3 as 2030 f/s on page 422.

On page 206 of "British and American Tanks of World War Two" by Peter Chamberlain and Chris Ellis Cassell 1969 (2001 reprint) the quoted velocities of the 75-mm M2 was 1860 f/s and the M3 as 2300 f/s. I assumed this was a typo and they meant 2030 f/s. Another typo on page 207 listed the weight of the 76-mm M1 series gun as 127 pounds; either it was extremely light weight or (after doing research) they meant 1207 lb.

On page 203 the 75-mm ordnance Quick Firing MK V and VA was detailed: a quoted velocity of 2030 f/s was given, improving the case for 2,030 being the correct velocity for the M3. They also gave the shot weight of 13 lb. for both the AP and HE. Perhaps that was a custom British load; who knows.

On page 112 of Tank - A History of the Armoured Fighting Vehicle by Kennth Macksey and John H Batchlor Ballentine Books a quote of 1850 f/s and 14.4-lb shot was given for the ..short 75 on the Lee They gave a weight of 15 pounds for the 3-inch anti-tank gun projectile on page 116 and for the sake of simplicity I eventually standardized on that as the weight for AP shot.

I had other sources and none of them dissuaded me from formulating velocities of 1850 f/s for the M2 and (to be neat) 2050 f/s for the M3, giving a 200 feet per second increase for about 10 calibers. It took a while to come up with the correct caliber length of the M3 which some people quoted as L/40 and others pulled other numbers out their asses; once I found out that 37.5 as the proper measure, I had to rethink the numbers that I was using calibers for.

On page 206 of "British and American Tanks of World War Two" by Peter Chamberlain and Chris Ellis Cassell 1969 they also gave the weight of the M2 as 783 lb. and the M3 as 910 lb. So far these have pretty much been the norms. This helped me guess at the weight of the 76-mm M1: each caliber length between the M2 and M3 added 22 pounds; thus the difference in calibers from the 75-mm M3 and 76-mm M1 L/50 times 22 gave a figure close to 200 pounds, which added to 900 gave an estimated 1,100 pounds for the 76-mm M1, add another 100 because the 76-mm chamber had to be longer and more robust. Later sources gave a weight of almost exactly 1,200 lb. for the 76-mm M1 (1210, 1207, etc.).

I was curious as to what velocity a 75-mm cartridge might have if fired from an L/50 barrel and did my math. I kept in mind that the actual barrel length of the L50 M1 (150-inches) would be longer than an L/50 75-mm (147.6-inches) so I used the caliber length of the 150 inches converted to a 75 for 50.8 calibers. A trifle difference but why mess around with minor inaccuracies? I could have done this in inches but the number of pounds and f/s per inch tends to be annoying when doing math by hand.

200 f/s difference between the M2 and M3 divided by the caliber difference gave around 22.2 f/s per caliber while 130 lb. difference between the M2 and M3 gave about 14.4 pounds per caliber. (I keep misplacing the actual numbers; so I cant blame others, can I? Except they have editors and umpteen readers to help)

Multiplying by the difference between the 75-mm M3 L/50.8 and 75-mm M3 L/37.5 times of 22.2 f/s per caliber gave around 2,300 f/s which was most impressive just 300 f/s shorter than the 76-mm M1. Multiplying the caliber difference by 14.4 gave a gun weight of 1100 lb. which was to be expected from the slightly lighter 75 blast chamber.

Recently I started noticing people quoting the velocity of the 75-mm M2 as being closer to 1,900 f/s. At first I passed this off as mass-typographical error, but I had a copy of Artillery Ammunition TM9-1901 June 1944 and knew I needed to double check my facts. There on page 101 the US Army quoted the velocity of the M2 gun as 1930 f/s and the M3 as 2030 f/s. Just a difference of 100 f/s.

So why were people quoting 1850 f/s? I checked the HE round velocities knowing they were lower than the AP rounds, but no go: the velocity of the M2 was 1885 f/s which is far closer to 1900 than 1850.

Reworking my velocity estimate I saw it drop to around 2180 f/s which I would personally round down to 2150. From a 55 caliber long barrel such as the British 17-pounder it would be a touch over 2200 f/s. Not a huge gain and it helps explain why barrel length and powder charge weight both increase to create higher velocities.

Out of curiosity I pulled up FM 23-95 75-mm Tank Gun M2 (Mounted on medium Tank M3) May 1942 and there it was on page 1: a velocity of 1850 f/s with AP shot and 1450 with HE rounds (which would be the normal charge not the 1800-1900 f/s super-charge HE round). Complete weight 783 lbs and bore length 28.47 (as close to 28.5 as need be) calibers, projectile weight 14.4 pounds.

Thus, referring to the official manuals can sometimes be misleading. Perhaps around 1942 the difference was around 200 f/s and new powders closed the gap by 1944. Perhaps a more rigorous method of measurements was used. Who knows.