[oldkim]

Yes, the recommendations are really for safety and overall keeping the steel plate in practical good use. Any closer and the force of the impact will eventually make the smooth flat surface become dented and weakened to the point that ricochets become more likely or you just plainly punch through them.

Ricochet: well overtime the plate will become cratered and you're just gambling after that.... is this a problem? Only if it hits you or someone else.

The 5.56 should not be a problem - the higher calibers will become a problem depending on distance and what type of round (steel core, "AP" etc).

Do know that AR grade steel is very difficult to cut by torch as the heat weakens the metal around the edges. Good luck but since this is a home range...

Now for your use - you could just use thick scrap metal and just replace. Good luck to you.