I milled up a front for my 4 inch barrel as it was shooting too high. I made 3mm higher and went out test fire for 25 yards. At 1st it was shooting so low it wouldn't hit the paper. I filed down at the range and keep test firing and filing till it was smack on centre with a 6 o'clock hold. The new sight ended up .030 higher. My feeling is go a lot higher and file to suit.
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