Quoted:
What is your barrel length? Some of the shorter barrels won't run Subs without modifications. You should reserve the drilling of the gas port to a last resort. You should also measure your hole and make sure you are only stepping up the absolute smallest amount (ie change to a different type of bit sizing).
In the meantime I am assuming this is a new upper? How is the gas key staked on and is it tight. How are your gas rings? What is the weight of your buffer. I believe the subs (or even all 300 blk) prefer the H2 weighted buffer. How old is your buffer spring?
The springs and buffer are good mods to have either updated or upgraded anyway and they are inexpensive. Start there before drilling.
Mike
16" bbl, all new, upper, lower everything. Not sure about gas block. Its my cousins rifle. I know it is a low pro block but don't know anymore about it.
Not sure which buffer either.
Was going to drill the next size larger and retest.
Will find out more info on buffer weight.
Thanks