John, that is an excellent book. I have a copy, too.

A couple points that have gone unmentioned, but should be:

There is much confusion associated with bullet penetration of various media. For example, the NE rounds make for relatively poor armor penetrators, but will penetrate fairly dense masses of soft obstacles; wood, sand, etc. Thus, what might make for a poor holer in plate might also make for a good penetrator of sandfilled sandbags. However, sniper pits were commonly built up using sandbags filled with rock, gravel, etc. Such a barrier is amazingly effectve at stopping even quite heavy bullets.

In fact, due to a variety of factors, penetration against soft targets like sand actually increases with range {to a limit, varying with caliber} and each caliber has an optimum range for penetration of wood, sand, gravel, brick, etc. The US military has guidleines for creating loopholes, manholes and mere penetrations of the various building materials as well, and extensive testing has been done to demonstrate how many rounds of each service caliber it takes to create such penetrations.

In addition, angle of impact makes a big difference to penetration depth as well.

Also, the German 13mm is a very impressive performer, similar to our .50 BMG and is light years more effective in holing steel than a .500 Nitro. The bullet diameter nothwithstanding. I have a bullet in my junk drawer someplace.

I myself have here on the place seen a round of steelcore {not AP} .50 BMG penetrate a 3/8 inch thick cold rolled plate, then a couple inches of airspace and then a half inch steel plate, this from a range of 400 meters.

Some curious experimenters could make an interesting day of shooting steel plate at 200, 300 and 400 yards with a variety of heavy NE rounds. Then do so with sandbags filled with a variety of materials. This sort of thing is quite instructive and would be quite interesting in light of various assertions made in various published sources.