T.Alan Kraus writes:

I have the choice of 4140, 1018, 12L14, 1045 cold rolled, W1 Drill rod,
O1 Drillrod, A2 Drillrod for a 1.125 diameter round piece that is going
to be subjected to approx 400 lb of load in compression and subject to
axial loads of approx 200 lb for brief times. Without heat treating what
would you choose, and if heat treating to R 30-35 what would you choose?
Obviously if heat treating the selection would be minus 1018 and 12L14,
am I right? By the way the rod is only going to be max 2 ft long and
supported for about 6" at one end.

Any of those alloys in that diameter will support much larger loads. I
would go with 1018 based on cost unless there is some other constraint.