Assuming that the 03 isn't one of the (possibly) bad early ones, I find I like shooting the 03 better than the M1. The 03 is more accurate and is not sensitive to ammo choices. The 03 will shoot any commercial 30-06 ammo. The M1 won't, most is loaded with powder that is too slow and it will damage the op-rod.

There is a gas port adjustment thingy that can be added to the M1 that supposedly makes it safe to shoot commercial ammo. I have not used it, so I don't know if it is a real solution.

M1 ammo must either be purchased through the CMP, or find a commercial brand made specifically for the M1. Federal/AE is the only one that I know of, I don't remember what the product number is. It may be 3006M1.

A good condition 03 is more rare than a good condition M1. When the CMP gets 03s for sale (less often these days), they are usually very worn.

Whichever you get, you may want a butt pad or a padded shooting jacket. The steel buttplate thumps you pretty hard.

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Common sense isn't so common.