I`ve 2 benches, one 30"x8' the other 30"x6'. One, the longer, is dedicated to reloading, the other is used for cleaning and other household chores.
Both are built on a 2x4 frame with a pair of 2x12s covered with a sheet of 3/4" plywood as a top. Plywood sides raised ~ 1" above the top help reinforce it and keep loose stuff from falling off the shelf/top in the back. The thing is heavy as hell, but it doesn`t move or flex no matter what I`m doing on it.

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