Have you used a core drill on a foundation wall?
I have used several different core drills. For horizontal drilling I have anchored the machine one I used expanding sleeve anchors others are held in place by hand and that one can be like a torture device these drills are slow and make a mess if inside.  Keeping constant pressure on the cutter will allow the cutters to do there job.
For the mess I found making a plastic sheet taped to the wall to direct the water into a bucket and pump it out to be the best method inside to control the mess.
I have had to split the slug of concrete once when the forms may have blown and the wall was thicker but breaking the slug allowed the cutter to go in further and finish the cut.