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Drilled holes are always oversized. Not an issue for drilling and tapping coarse or deeper threads (deeper thread depth, not hole depth), a problem with fine threads that are shallower.
For a one off job you can use a drill about 0.002-0.004 undersize at some increased risk of tap breakage. For an exact hole size drill under and ream up to the exact size required. Numbered size chucking reamers are not very expensive, try MSC.
Fixturing is required to produce an exact hole diameter. Even clamping the gun to a drill press table, drilling the hole, then chucking a reamer and turning by hand without ever moving the gun will produce a much better hole (rounder and more exactly sized) than trying to free hand.
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