Steeping Grains to improve kits

[Chris The Fish]

Ive just got hold of half a kilo of both crystal and chocolate malts, with a view to using them to steep and add to a kit (namely John Bull Stout).

I fancied experimenting using one of the above in the stout, however im unsure which one to use, how much to use, how to use it, and what type of flavour it would bring to the brew.

if any of you out there has any experience of using this process id love to hear your pearls of wisdom, ive done a brewers choice ipa before where both are used in tea bags, however this is the only experience i have of using grains.

cheers in advance

Chris