I have done this with my bit shorter 12 x 20. The issue is twofold when drilling deep holes, Chip clearing, and access to the depth.
The last three I've done were in SS, which is a real bear compared to 1018, but I would follow as I've already done given that material. Start with a 1/2 D hole drill about 1-2" deep, for ease of starting the next size bit 5/8 bore a pocket 1/4 deep that size, that way the 5/8 will start on center, no go almost as deep as the 1/2 bit, but not all the way, as you want to keet a good pilot hole for the 1/2 to follow, now back to the 1/2 drill and another 2 ".
Why this way, CHIPS, that 1/2 drill will produce almost twice the chip as the 5/8 next step drill, and the 5/8 has lots more room for chips. That 1/2 will need to be cleared less often since the chips dump into the 5/8 bore, rather then jam the flutes in the deeply buried 1/2 drill. continue down the bore 1-2' then step to 5/8. Ebay has both 1/2 and 5/8 long drill, be sure to buy as much flute length as you can. There are Carbide long drills on ebay, pricey, I have 5/8 15" long just for the cannon barrels as I recall around $80
All the drilling I do for this job is with MT2 taper shank drills, ebay is the source for all the drills like this. There is a drill called a core drill, it looks like a reamer, it has no point and in 1" size has 4 flutes MT3 shank. These things are GREAT, the chips shoot out the top of this in the form of a straight ribbon, and fast, The flutes for a 1" are about 7" long, I ground down an MT extension so I can drill 11 1/2" deep. I recently bought a NOS 15/16 core drill for $30 buck on ebay. If you don't have a MT3 in the tailstock, carbide will easily turn down the shank its hardened but not that hard.
If you need it I will grind an MT2 on a drill for you.
When stepping from the 5/8 to 1" I bore a pilot same as the step from 1/2. Your issue if trying to bore a hole that deep is tool flex, in a 1/2 hole a insert type BB would be 1/4 shank, even at a 5/8 bore a 1/2" bar only can take you 3" deep
