If you keep it to about 1% of the grain bill it will lend an extra bit of complexity in the dark malts, and a a dry crisp almost bitter finish which I personally like. You may need to drop the hops by a couple of IBUs to compensate for that finish. If you get up to 5% black malt you will be in the charcoal, ash, chewing on a heat bead type flavours, which need a lot of other flavours to back them up, or stand out.
Thanks GL. Looking back through my early records I got RB and RM mixed up and ended up with 10% RM. It was enough to turn me of stouts for about 5 years now. But I think I will give another crack as I have made some great Porters with a little RB. So I will have another go when kegs become available.
4000.00 gm Pale Malt, Ale (Barrett Burston) (5.9 EBC) Grain 73.39 %
800.00 gm Barley, Flaked (Thomas Fawcett) (3.9 EBC) Grain 14.68 %
200.00 gm Amber Malt (43.3 EBC) Grain 3.67 %
200.00 gm Chocolate Malt (886.5 EBC) Grain 3.67 %
200.00 gm Roasted Barley (Thomas Fawcett) (1199.7 EBC) Grain 3.67 %
50.00 gm Black Malt (Thomas Fawcett) (1300.2 EBC) Grain 0.92 %
30.00 gm Target [11.00 %] (60 min) Hops 33.4 IBU
20.00 gm Fuggles [4.50 %] (15 min) Hops 4.5 IBU
0.50 items Whirlfloc Tablet (Boil 15.0 min) Misc
11.00 gm PH 5.2 Stabilizer (Mash 60.0 min) Misc
1 Pkgs Nottingham (Danstar #-) Yeast-Ale
Steve