Brewing my first AG batch next Saturday... How much extra grain should I buy...

...if I'm unsure about my mash tun efficiency, and want to ensure I hit my OG at boil volume?

Here is the grain bill;

10lbs 2 row base
.5lbs CaraPils
.5lbs Crystal 60L

6 gallon boil

pre boil gravity: 1.047 (assuming a 70% efficiency)

I'll be buying the grain at a LHBS during the week. Is it customary for the LHBS to grind the grain per customer request? That is, if I tell them how fine or course to make it?

Thanks in advance.

I've never been that concerned about that. But if you are you could buy a couple pounds of DME just in case.

I've done two AG beers now and I think you will be surprised at your efficiency for a beer at that gravity. Judging from that experience, I think you will be absolutely OK in hitting your target gravity with that grain mill.

My LHBS has a mill that customers can use after they purchase. Worked well for me.

I agree with both, you shouldn't have any trouble hitting your OG, but it never hurts to have a little DME around.

Your LHBS has probably crushed tons of grain for customers. If they couldn't do it well, I doubt they would still be in business.

Since you OG is moderate, I would assume 65% efficiency. Then, if you come out high, you get more beer or a slightly higher OG.