A couple Observations....

[WyomingBrewer]

I have 3 all grain brews under my belt that are currently bottle conditioning. I have ,as of yet, not tasted one. I started with extracts like lots of us did so I have roughly 12-15 home brews total made thus far. Here are a few things I have noticed;

1. My all grains FG's typically end up lower than even the recipe's projected. Of course they are projected using extracts.

2. My OG's also have ended up higher for the most part.

3. I am getting really good efficiency using batch sparging in two phases. ( or maybe I'm not and I will learn I have been doing it wrong, but its hard to argue with the hydrometer)

Here are the three I made and the numbers involved.

***** Creek Clone

OG projected @ 1.061, actual 1.068
FG projected @ 1.014, actual 1.01
ABV projected @ 6.1%, actual 7.1%

What I am calling Plain Ale (used beer recipator for the numbers)

OG projected @ 1.044, actual 1.050
FG projected @ 1.010, actual 1.005
ABV projected @ 4.4%, actual 5.9%

Fat Tire Clone

OG projected @ 1.050, actual 1.048
FG projected @ 1.013, actual 1.005
ABV projected @ 4.8%, actual 5.6%

So it would seem then, that it is common for the FG's to end up lower and therefore your ABV being higher. Or it may be the yeast? I had a bunch of Nottingham on hand so I passed on buying more yeast to use up some of what I had. I know that it can not be considered a true clone at that point, but oh well. So is it common or the yeast?

 

[Dawgs47]

The OG will be a product of your brewhouse efficiency. This will come from your mashing/sparging methods and time. You should adjust your recipes as you get to know your system more to reach the OG you are shooting for.
The FG will be a product of your yeast and fermentation conditions. I believe Danstars Nottingham is high in Attentuation and you should expect a lower FG when using it.

 

[Hammy71]

When my FG comes out lower than expected, it's usually because I had trouble maintaining my mash temps. Lower temps usually makes a more fermentatble wort, and so a lower FG

 

[briegg]

When my FG comes out lower than expected, it's usually because I had trouble maintaining my mash temps. Lower temps usually makes a more fermentatble wort, and so a lower FG

This ^^

I would ensure your thermometer is correct around the 150 range. If you mash even a couple of degrees too low, you'll end up with more fermentable wort...i.e. lower FG.

 

[BigEd]

WyomingBrewer, I agree with Dawgs47 comments and would add that AG beers will tend to be more fermentable than many extract beers which is another reason your FGs are lower.