Here's one of the 8 inch siege mortar vent shield.
I use 3/8 inch plywood fastened to a 4x4 for my 24 pdr mortar, and 3/8 inch plywood with a bracket that fits over the fulcrum on my 8 inch mortar.
Pretty hard for a piece of wood to look pretty after twenty or so years of rough use.
Thanks for the photo and info, Norm. Thinking of that 3/8" plywood board absorbing the punishment delivered by such an intense degree of energy, not to mention the abrasion caused by all the ejected friction primer tubes hitting it at near point blank range, and for a period of 20 yrs., no less; and mind you, we're not talking about a reduced scale model here, we are now dicussing the blowback coming from the vent of an 8-inch siege mortar (the real thing, BTW).
Well, what can I say other than: I've evidently really been underestimating the strength of plywood for a good many years; or have I?