Like I said a while ago, throw your bit of metal in the car, drop into a
local engineering shop and give them the equivalent of a six-pack.

They in turn will drop your round bit of metal into the jaw of their lathe
and spin it round with a drill bit in the tailstock and drill a perfectly
central hole of any size you desire in the end of your cylinder.

In fact, for the cost of a sixpack, they will probably even drill both ends
to different sizes.

Hope this helps,
Peter