Ram Mark II manual

[45jim]

Tolerance in cross section is not a function of location of manufacture but one of process control. Arbitrarily selection of a tolerance of 0-5% and calling it a "rule of thumb" isn't even rational as tolerance changes as surface area increases. Current thickness tolerances are about 2.5% for off the shelf rolled armour (up to 60" width) and most vehicle companies require tolerances closer to 1% (e.g. CMS 21). The standards exist for a reason, ballistic performance can be compromised by stacking tolerance in the wrong direction. Cast standards are also good, examine a cast iron engine block for example.

I wonder if you have misunderstood the notations on the cast US armour spec you elude to. Anyone who manufactures anything to a drawing makes it to the drawing (as close as possible within the confines of the process) so if it says 2" on the drawing then the final product will be 2". If there is a notation on the drawing that states "equivalent to 2" RHA" it most likely relates to the ballistic standard that that section must achieve as RHA is the standard by which all other metallic armours are compared.

The basis curve you attached has nothing to do with armour protection, it is a graphical representation of a simple mathematical calculation of cross section at various angles of attack. This is useful in calculating the reduction of weight achievable by using thinner sloped armour. You can tell this by the nice slope, penetration performance does not generate such a nice predictable curve. It quickly changes to ricochet at high angles of attack. If you were using this curve to predict armour performance you have a problem because as you approach 90 deg the thickness becomes the height of the armour sample.

Worthington knew what he was talking about regarding armour and that using NATO angles (normal angle to zero) is nice but it fails to take into account potential engagement angles in combat.