Finally figured out how to fit the drill in that tight shaft

I ran into a similar issue when we had to pull utility lines through a foundation block that was surprisingly thick. The wall was just too tight for my standard angle setup and the drill kept bouncing off the edge of the opening. It felt like I was fighting the wall instead of drilling through it.

What finally worked for me was switching to a rotational hammer with a much lighter bit. The key wasn't the size of the tool but how I secured the entire setup. I used a piece of sturdy scrap lumber clamped to the existing framework, wich gave me a solid anchor point for the drill itself. This prevented the bit from wandering into the void when I engaged the impact setting. It took a bit of patience to get the alignment right because the bit kept wanting to run off center, but once I got the pressure and the angle just right, the breakthrough was quick. It’s all about having a stable back-stay so you aren't just relying on your hands to keep the drill perfectly still while it works.

I ran into something similar when I was trying to run a few smaller conduits through a masonry pillar. It wasn't a single massive line like the riser you described, but trying to keep four holes perfectly aligned in such a restricted area proved challenging. I found that the issue wasn't the depth, but maintaining the correct spacing and perpendicularity without a huge housing to hold the drill steady. The concrete itself was quite crumbly near the edges, too. My method involved using a simple template cut from a piece of thick acrylic. I transferred the center points for the holes onto the template first. Then I simply clamped that acrylic guide to the concrete surface and drilled through the center of it. This setup essentially handled the alignment for me. Instead of constantly adjusting my drill angle to stay within millimeter tolerances, the rigid plastic held the path stable while I worked. It meant more prep time for the template, but it prevented all the wandering and misalignment that comes from trying to visually mark and keep the bit steady in such a cramped space.

The one thing I'd add from my own hours wasted on a cinder block chimney chase is that drilling a smaller pilot first saves a ton of grief, since a wide core bit will skate all over the face untill the guide teeth actually bite. I go pilot, then swap to the coring bit and let the ring center itself over the starter hole, which also keeps the dust down a little if you pause and vacuum between short runs. Curious wheather the OP found the scrap steel jig stayed square over several holes, because mine always seemed to creep a degree or two by the third one.

Update: took the advice about starting with a pilot hole and it made a huge difference, the core bit finally stopped skating around the face. Still fighting the alignment though, the jig I rigged keeps walking slightly as the bit gets deeper. Anyone found a good way to keep the jig from shifting mid-hole, or is it just a matter of clamping the heck out of it?