Trying to figure out hop utilization for full boils

[JohnT]

I've got a Brewers Best kit (bb) that I'm trying to plug into Brewtarget or Brewsmith so I can figure out the hops for a full boil.

I've plugged in all the ingredients and set up the equipment as a 2.5 gal boil w/2.5 gal top off. Problem is the IBU's don't come out right, for the partial boil, they are way to low. 18 when the kit specifies 31-34.
If I can't replicate the original recipie I won't be able to let the software change it to a full boil.

Any Ideas where I'm going wrong?

 

[JohnT]

Maybe if I add the recipe someone can tell me where I'm going wrong.


BeerSmith 2 Recipe Printout - http://www.beersmith.com
Recipe: bb milk stout test
Brewer:
Asst Brewer:
Style: American Amber Ale
TYPE: Extract
Taste: (30.0)

Recipe Specifications
--------------------------
Boil Size: 2.30 gal
Post Boil Volume: 2.08 gal
Batch Size (fermenter): 5.00 gal
Bottling Volume: 4.75 gal
Estimated OG: 1.052 SG
Estimated Color: 24.3 SRM
Estimated IBU: 18.9 IBUs
Brewhouse Efficiency: 72.00 %
Est Mash Efficiency: 0.0 %
Boil Time: 60 Minutes

Ingredients:
------------
Amt Name Type # %/IBU
8.0 oz Caramel/Crystal Malt -120L (120.0 SRM) Grain 1 6.2 %
4.0 oz Chocolate Malt (350.0 SRM) Grain 2 3.1 %
4.0 oz Roasted Barley (300.0 SRM) Grain 3 3.1 %
3 lbs 4.8 oz Dark Liquid Extract (17.5 SRM) Extract 4 40.7 %
3 lbs 4.8 oz Pilsner Liquid Extract (3.5 SRM) Extract 5 40.7 %
8.0 oz Milk Sugar (Lactose) (0.0 SRM) Sugar 6 6.2 %
0.50 oz Warrior [15.80 %] - Boil 60.0 min Hop 7 17.1 IBUs
0.50 oz Willamette [4.60 %] - Boil 10.0 min Hop 8 1.8 IBUs
1.0 pkg Nottingham Yeast (Lallemand #-) [23.66 m Yeast 9 -


Mash Schedule: Single Infusion, Light Body, No Mash Out
Total Grain Weight: 8 lbs 1.6 oz
----------------------------

Sparge: Remove grains, and prepare to boil wort
Notes:
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Created with BeerSmith 2 - http://www.beersmith.com
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