Is this a good grouping at 300m

[bd1]

Reads like somebody has already filed the front sight post to facilitate longer distance shooting with fewer clicks up at the rear. If your rear sight is all the way to the bottom that's what you'll have to live with. Sometimes the forward edge of the aperture ladder can be beveled to give the shooter 2 to 4 more clicks down. Worth taking a look at. Best things you can do for your shooting improvement will be 1) more trigger time and 2) load your own ammo with good bullets.

[The Wizard]

If your rear sight is "zero'd" out in elevation and you are still 6 inches high at 100 m, there is something definitely wrong with your rifle. According to FM 23-8, Basic Field Manual, U. S. Rifle, Caliber .30, M1, dated 30 July 1943 the initial sight setting for a 200 yard zero is 10 click of elevation and windage at zero.