RE: port presures
The M1 is a special case because its oprod is fairly delicate and complex curve to it that is necessary for it to function correctly- high port pressures will bend the rod out of alignment while low port pressures won't cycle the action reliably. You can only use a narrow range of powders and bullet weights in a M1, and most factory loads aren't good for the M1 either.
BARs and Remingtons don't have such problems, so use whatever reasonable worked up loads you want with whatever powder is reasonable for the cartridge- H-4350 or IMR 4350 (the two are not interchangeable despite their similar name) would be a good all around powder for the '06.
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