I have H-P's book also.

He's the one.

1/4 inch mild steel seems likely, depending on range. I do not believe 1/2 inch hardened plate would be phased one bit by a .470 Nitro at any range. Depending on range, 1/2 inch mild steel maybe.

As for WD use of oddball guns, the Brit military has something of a hoary old tradition of borrowing any'ole shootin iron and did so early in WW1 for the stated reasons, and later at the begnning of WW2 when we were collecting donated guns in barrels at sporting goods stores, along with binoculars and timepieces for shipment to the UK. I've always wondered how many of those altruistically parted-with guns actually made it to Blighty, as opposed to the gun room of the store owners...

Anyway, here's a piece of heavy 3/4 inch thick cold-rolled steel plate shot with a few different rounds. Shot at about 15 meters. The .375 H&H and 7mm Rem Mag noted. This is NOT hardened AP. Railroad fishplates I have shot evaporated these bullets with virtually no dent at all. All of those were old plates, and I am not certain if their toughness was due to previous heat treatment or years of work hardening under the rails. I suspect they were heat treated to a spring temper whih is tougher than cold rolled plate and quite resistant to bullets.

JOHN and any one else reading this: If you have not shot plate before, please be careful. I know the SASS guys shoot it all the time fairly close up, with low velocity lead bullets, and the Silhouetta Metallica fellows shoot it with high velocity jacketed bullets from far away, but high vel jacketed bullets shot on plate up close can be very dangerous. I took a bullet fragment through my right index finger {support hand} a few years ago and a friend took a chunk of a 20mm Lahti round all the way thru his forearm. Stuff pours back from the cratering, can be and is dangerous.