Biggest issue I've had material wise is drilling 304 stainless. It eats up drill bit ends and does everything it can to harden as you drill. The procedure I do on it is technically coring, but our coring bit is only like 3-4" long, and we need to come in about 8-10". I've been told a coring bit for that length would have to be custom ordered to the tune of about $1400 for 1 bit....so we drill.
