How to crush specialty grains for steeping?

I am going to try to brew an extract recipe that calls for steeping with specialty grains - the first time I've tried it. I have all the ingredients, but am uncertain about how to crush the grains.

I began trying to crush the grains by putting them in a ziplock bag, and running a rolling pin over them, per some info I found on the web, but even have questions about that. How much do I need to crush them? It seems that as I crush them they actually poke holes in the ziplock bag and I see some powder coming out. Am I crushing to hard? At the same time, I see many grains that are not even cracked. Should I be crushing a smaller amount at a time?

Thanks in advance for any input.

You just want to crack the hull if possible. Bash it rather than rolling it.

You're not making flour...just cracking the grain hulls. A little powder is ok. All powder is not advisable. Try crushing them in a single layer with only one or two passes of the rolling pin.