With Minecraft 1.7.10 and a recent build of IC2, a mining laser in horizontal mode can mine about 56 sand, and nearly as much dirt or netherrack. When mining stone, it penetrates about 7 or 8 blocks iirc, and goes a bit further if it encounters ore.
With Minecraft 1.10.2, it only mines about 15 sand or 5 stone (I haven't got exact figures for other materials), and stops sooner if it encounters ore.
I found some entries in the changelogs that might be relevant, but I don't really understand why this has changed.
"Mining laser, misc fixes."
"Mining laser is now 9 times more fun"
I'm not sure what that is supposed to mean - I doubt it's referring to scatter mode, because that generates 25 beams.
"Fix the mining laser range."
Unless the 1.7.10 range was somehow a lot higher than intended, it doesn't seem fixed to me.