Antipode of round bar

I am building a bolt with the charging on top. The lug needs to be 180 degrees from it. How does one set it up in the mill to mill the hole for the lug? I don't have a vertical rotary table. I suppose this is an elementary layout procedure so please don't let my ignorance offend you. Thanks for your instruction.

I am building a bolt with the charging on top.

Don't really understand this statement. Do you mean you want to build a bolt action rifle with the magazine on top (sort of like a Bren?)

Bren light machine gun

Make sure the shooter can see the sights.

I ment to say charging HANDLE on top, lug on bottom. I have found a solution to the problem, I am certain there is an easier way to do it, however, here is how it could be done.
Chuck round bar in lathe.
Face the end thereby locating the exact centre.
Place a sharp tool in the Tool post and scribe a line from the centre to the outside of round bar on y axis.
Scribe a line in x axis with tool you just centered where you want to bore a hole.
Rotate chuck 180 degrees.
Match the Tool up with the scribe mark on the end of bar checking alignment of y axis to get 180 degrees.
Scribe a line on the x axis where you want to bore a hole in the other side of bar at a different location on the x axis.
I feel certain this is the most difficult way to lay out the hole locations, but I believe it is one solution to the problem.
Suggestions?

An easier way. Mount bolt (1" bar) in square 5c collet holder. Rotate 180 degrees for both features.