why didn't my biscuits w/ self-rising flour rise?

[elaineandmichaelsmommy]

so dh got me one of the paula deen cookbooks for christmas and i made her sour cream butter muffins. they taste great but they didn't rise. anyone know why?

2 cups self rising flour (made my own-added 2tsp salt and 3 tbsp bp)
1 cup butter
1 cup sour cream

combine flour and butter,add sc and bake in muffin tins for 10 min. I don't understand why they didn't rise.

tia
jen

[annex]

How old was your baking powder? I didn't know until recently it needs to replaced every 6-12 months:

http://www.joyofbaking.com/bakingsoda.html

"To test baking powder's effectiveness: mix 1 teaspoon (5 grams) baking powder with ½ cup (120 ml) hot water and the mixture should bubble immediately. Store in a cool dry place and it should be replaced every 6-12 months."