Question about calculating gravity pts in recipes in Palmers book

Brewing Processes
1

Hi.  I have read John Palmers book “How to Brew”. In it he goes over calculating gravity points based upon lbs of particular malt and volume of wort collected after mashing.  Specifically in chapter 18, Extraction and Yield on pg 288 he utilizes an equation, Max_PPG x (lbs_of_Malt/gal_of_wort_collected) = maximum number of gravity pts assuming 100% efficiency.  In this example (table 18.4), gal_of_wort_collected = 6 gal. For the first malt listed, 6.5 lbs of lager malt, the lbs_of_Malt = 6.5 and Max_PPG is found from his table18.5 on pg 289 to be (first entry) = 37.  So 37x(6.5/6) = 40.08.  He does the same for the 4 other types of malt listed in table 18.4 and sums them up to 51.66 pts or a hydrometer reading of 1.052.  To calculated brew house efficiency one would (as he does in example) take a hydrometer measurement after mashing out 6 gal and if they recorded 1.038 take efficiency = (measured points/max points) x 100 = (38/52)x100 = 73%. 
In chapter 23 he lists his recipes which include the gravity pt calculations.  On pg 404 is the glorious black ipa recipe.  He lists the malt bill as:
12 lbs pale ale malt:  Gravitypts: 48
2.5 lbs wheat malt:    Gps: 10
0.5 lbs caramel 60L:    Gps: 1
0.5 lbs Briess Black Prinz wheat malt:    Gps: 2.

But when I use method in chapter 18, I get the following using table 18.5 along with the fact that all his recipes specify collecting 7 gal from mash,
12 lbs pale ale malt, Max_PPG=37 so Gps = 37 x (12/7) = 63.4, say 63.  Way over the 48 specified in the recipe.  Doing the same for the other malts I get:
2.5 lbs wheat malt: Gps = 14.
0.5 lbs caramel 60L: Gps = 34 (compared to 1?!!!).
There was no entry in table 18.5 for the Briess BPW malt so I’ll leave that out.

So does anyone know what I’m doing wrong?  This is a simple example, but I’m going to need to know how to do this for any recipe that does not explicitly state the gravity points.  For example Steele’s book on IPA gives OG and percentage of malt types requiring me to calculate the lbs of each malt.  Ive tried doing the same for a couple more of Palmer’s recipes and always I get a much larger numer.

Could it be that table 18.5 is for demonstration purposes only?  Ie, do I need to get the actual Max PPG from the malt analysis as perchaced by store that sold me the malt?

2

Please excuse typo on caramel malt, my calculated gps were 2.4, not the 34.  Much better but still higher than 1 which is what he calculated.

3

I wouldn’t overlook the fact that the book may be wrong.

4

No, because in addition to the this value of GP, there is added the GP for the other malts.  But perhaps the value listed is not the absolute maximum but the value after considering a brew house efficiency of 76%? But why would I compare my measured hydrometer reading to something short of max value?

5

I am sure that this may have been mentioned by others but to simplify,  63 is the max GP you can get out of the base malt, so you are halfway there with your calculations.  You need to multiply the max GP number by the brewhouse efficiency value to get the real extaction number for the malts using your system.  If your brewhouse efficiency is 75%, you get 63 x 0.75 = 47.25 GP (round to 47) which is in line with the recipe in Palmer’s book.  You have to do perform this part of the calculation with each malt based on it’s published extraction number as not all of them may be 37 gravity points per gallon.