If you know how to make a "D" bit,they drill with great accuracy. I made a 9/16" D bit out of drill rod,and drilled a 16" deep flintlock pistol barrel out of very tough propeller shaft bronze in the lathe. It was only .002" off center where it emerged.
A D bit is a very old design,but it is still a good one. They bored cannon with them hundreds of years ago.
You need to start a carefully drilled,then single point bored hole that is 3 or 4 times the diameter of the D bit deep. The D bit should JUST be able to enter the hole. It must be frequently withdrawn to clear chips,as it hasn't much capacity to hold chips. If you start the bit carefully,and don't drill too aggressively,it will do the job.
Twist drills are often not real straight to begin with. Since they are made in the shape of a spiral,they are also not very rigid,like a coil spring. The D bit is made by taking a piece of drill rod the correct diameter,and milling it down to a few thousanths above half diameter for,say,1 1/2" for the size you want. Leave the uncut half of the D bit .252" thick. Harden just the last 1/2 inch of the bit,so as to not warp the drill. 01 would be safer than W1. Grind the end of the bit at a slight angle,so that the CUTTING SIDE is a little ahead of the trailing edge. Also,grind maybe 10 degrees of clearance angle below the cutting edge,or the drill will not cut. You may have to touch up the edge a few times for each hole,and keep the false edge from building up. The D bit can be left at full diameter for about 3",but you should reduce the diameter maybe 1/32" for the rest of the length of the drill rod. This reduced surface does not have to be precision. It just provides clearance for the body of the drill so it doesn't rub,overheat,and gall in the hole,becoming permanently stuck.
Others may ridicule this D bit,but I know from personal experience that it does work. The solid portion of the body,which bears against the hole, will not flex,or let the bit wander off course like a twist drill will.
A gun drill really operates on the same principle as a D bit,and with pressure fed coolant going through it,and a carbide tip,it is better as it flushes the chips away. If you don't have that option,a D bit would do the job. The bronze I drilled with mine was VERY tough. I also drilled a same length genuine wrought iron barrel with it. It still came out very accurately,as it did in the bronze.
Be sure to use plenty of kerosene lubricant.