I went with DeplorabusUnum‘s suggestion and constructed a “matrix” of roofing nails through aluminum flashing sandwiched between two pieces of wood. I measured the oven racks and made two matrixes with 169 (13x13) nails each to fit the racks. I completed one just to try everything out and see if it was viable enough to spend the time completing the second one. It’s working pretty well...the wadcutters I tried first were surprisingly stable. I thought it was going to be like dominos falling when I first picked it up, but slow and steady wasn’t too bad. It should be even more stable with shorter, lighter projectiles like 124 gr. 9mm. Drilling 169 straight holes and nailing in the 169 nails was pretty tedious, but I got it done. Having a good drill press sure helped! I used 1/2” and 5/8” hardwood ply for the wood, since I had it on hand. I only had to drill one set of holes, since I sandwiched the two top halves of the matrix together and drilled through both. I didn’t drill the bottom piece of wood, I wanted the nails to penetrate the flashing and anchor in the bottom piece, which actually worked pretty well. I placed the two pieces of wood with the flashing between them on an old piece of 1” boilerplate for nailing. My idea was to have the nails bottom against the plate so all of the nail heads would be a uniform height. It worked ok, but the nails needed to be a uniform length and they were not. Just enough variation to give slight height differences. Tricky part was running the nails in evenly, I had a couple that ended up with heads canted slightly from horizontal.
Here’s a couple pictures of my construction and first batch in the oven. I ordered some Eastwood PC, but won’t have it for a few days. Had to make do with the HF white. Sorry I didn’t take more pictures. I’m really bad about taking pictures of each step; I get focused on what I’m doing and forget.
Edit to add: Just got my first batch out of the oven. How do they look? Should I do a second coat, or is one enough?