Any time you steel for a backstop, be aware the constant shooting against it will create dents, and perhaps miss-shape an area. Rounds fired into curved steel can come back at very unknown and unexpected angles. It has been known to have caused injuries. High powered rounds like those you mention need to be contained in the backstop, such as the railroad ties mentioned above. Also, there are many different grades of steel, and some are much softer than others. I have fired .222 Remington at a 1/4" boiler plate and it totally penetrated the steel.

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H Richard
SWCA1967 SWHF244