Drilled at an angle and all you need is proper bit to correct depth.
I use a pieces of tape around shank of bit and stop when I get there.
Easy as Pie.
See here: http://arlower.ray-vin.com/ar15/chapter08.pdf
I got 25.00 in this one but the rear hole needs to be drilled deeper (Easy to do indicated by red arrow).
I will let you have it for that shipped if you want it.
I use this one : https://www.80percentarms.com/products/easy-jig-gen-2-multi-platform-ar-15-ar-9-and-308-80-lower-jig/
The absolute best one I have ever used.
I sold all my others and this is the one I kept.