Watch Hammer drill vs. rotary hammer
. The guy is drilling through concrete pretty easily with what he says is a 1/2" bit. I'm not sure he's right about the size though.
I was told that I could drill 1" holes in concrete with a hammer drill occasionally
if I give the drill a rest and don't do it straight. Maybe you're using the wrong or a worn out bit or maybe you're not in hammer mode. Make sure it's a bit made for hammer drills. You could also drill a pilot hole. "45 minutes to drill a 3/8" hole 2.5" deep" just can't be right. I never used a hammer drill though.
Oh...beach stones...I know nothing about the hardness of beach stones