I just sent this off to the Yahoo mill-drill group and decided some rcm folks would probably be interested, too.
Last week's postings about the undersized through-holes in 1-2-3 blocks reminded me that I'd wanted to try something. So I dug out the 3/8" carbide masonry drill that I'd bought for a quarter at a garage sale last summer, took a 1-2-3 block, and tried opening up a hole. Loud, hot and lots of little blue chips. And a 3/8" hole. Drilling one "web" at a time - meaning four webs to get through on the 2" dimension - and letting everything cool between times, I got through six webs before the drill tip broke up. So I've got one hole opened up to 3/8" through the 2" dimension and another halfway. Not bad for a quarter. Now to find a few more 3/8" masonry bits.
Tove