The reason the 1/8" drill seems too big is because the flash channel is plugged with hard hard carbon. Start with a smaller drill, and work larger up to 1/8", and go no larger.
There may be some confusion in terminology, There is the primer pocket, then the fire channel also called the flash channel and then the fire hole also called the flash hole and then the powder charge. The fire channel or flash channel is where the 1/8" or a little smaller bit is used by hand for cleaning. I use a short length of SS wire to clean the fire hole or flash hole. Hope this helps. https://www.google.com/search?rlz=1...64k1j0i22i30k1j33i21k1j33i160k1.0.ST27kODa6AQ
I carry bullets in sabots in a tube. On that tube I have taped a half dozen 3" lengths of copper wire the size of the flash hole and I take a second to run one thru it on each reload in the field. I've never had a hang or mis-fire while hunting and this is just a little extra to ensure it doesn't happen.
I thought I was doing a good job of cleaning mine. Read on here about using the drill bit last year and thought I’d give it a try. I was surprised to say the least.
I've had great luck with the Eezy-Breech Cleaning Tools (see picture below). There is a combo bit holder/fluted collar which cleans the primer pocket and the flash channel with 1 tool at once, and the smaller bit holder which cleans the flash hole. Yes, other devices (drill bits) can clean them just as well, but as this comes all together at a low cost * -- and also as I'm a sort of "tool snob" and like neat "gadgets" -- I found this tool set to be a terrific addition to my Omega cleaning kit.