I will follow your instructions.
It is not obvious to a newbie that such experienced techniques are so critical.
If I understand your comments, I drill the hole and then ream prior to proceeding to the next hole (no movement of the work). It appears that a relatively short length reamer will be required to preclude large movement on the Z axis. My DRO is one of the Chinese version that displays position to 5 decimal places so the hole location should be accurately placed.
Not reamed, bored with a boring head. A reamer will still follow a drilled hole that is not true. A boring head will true up any walking off center the drill bit did which is pretty much guaranteed to happen with deep hole drilling like this.
In general terms, when holes need to be very accurately sized and exactly on location, boring is the accepted method. Drilling a starter hole to get most of the meat out is how to start of course, just leave enough material for the boring bar to true things up.
I went through the same problems you are experiencing. If I recall correctly, Cutter is the one that suggested boring the holes as the best method. He was absolutely correct ! The hole positions were orders of magnitude improved.
Making the bolt carrier in 2 pieces also helps a lot, the depth of the holes are much less than one piece. Although its 2 parts instead of one, its actually easier that way with better results.
- bruski, Roller, Cutter and 2 others like this