Nose Shape of U.S. 76mm HVAP and 17 pdr APDS

[rexford]

U.S. and British data give differing views on the slope effects of APDS and HVAP, and the main projectile difference causing the differences would probably be nose shape.

Were the nose shapes on the British 17 pdr APDS and U.S. 76mm HVAP rounds similar or different? Both rounds had 3.9 pound cores with 38.1mm diameter.

The following is a comparison of slope multipliers that convert angled hits to an equivalent thickness of vertical armor:

76mm HVAP

1.35 at 30 degrees from vertical

2.26 at 45 degrees

4.24 at 60 degrees

17 pdr APDS

1.23 at 30 degrees from vertical

1.82 at 45 degrees

3.51 at 60 degrees

For British 37mm APDS (an experimental round), the penetration vs angle curve results in the following slope multipliers:

37mm APDS

1.39 at 30 degrees from vertical

2.01 at 45 degrees

4.01 at 60 degrees

For both sizes of British APDS, the slope effects at 45 and 60 degrees are lower than U.S. 76mm HVAP. This suggests that the 45 and 60 degree slope effects may have been a function of nose shape, but a comparison needs to be done.

At Isigny, 17 pdr APDS made it through the Panther glacis with an impact angle of 57 degrees from vertical due to ground tilt. Applying the British slope multiplier for 17 pdr APDS to 82mm at 57 degrees results in about 2.9 x 82mm or 238mm vertical, while the 76mm HVAP slope effect would result in 82mm x 3.6 or 295mm vertical.

Based on British data, 17 pdr APDS could penetrate 238mm vertical at about 900 meters and could not penetrate 295mm vertical at any range.

With regard to 17 pdr APDS against Panther, it might be useful to halve or third the APDS that is given to British tanks and TD's with 17 pdr guns due to the following factors:

1. rounds were erratic in behavior and often failed to hit known targets at known ranges during firing trials

2. rounds were erratic in behavior and might fail against a given plate one time in a test and then succeed at a much lower velocity

3. Panther glacis quality is not 0.85 for all tanks but really was quite random.

[rexford]

rgriest1 on the Yahoo! Tankers site explained the different slope multipliers on the basis of APDS cores hitting the armor directly, whereas HVAP has a lightweight carrier which impedes the angled penetration and boosts the slope multiplier.

[ March 30, 2004, 03:30 PM: Message edited by: rexford ]