Wow, I wasn't expecting calculations! Thanks for the reply!
1) They're bottle conditioned, but I don't think that's the problem. His was the only one (to my knowledge) that's done so much as foam over. Even if the last few bottles had more sugar, I have no way of knowing which ones were actually the last ones bottled at this point. It may be worth noting that butterbeer I had I poured hard into the glass (again, I like my beer almost flat) and about 1/2 - 2/3 of it was head initially. But, again, not even a geyser for any bottle to my knowledge.
2) At the time my process was to rinse out a bottle to get the majority of the yeast cake loose, rinse again, and let a bit of hydrogen peroxide (enough to cover the bottom) sit in it for 1-2 days, rinse again, then sanitize at bottling with one-step. My process now is pretty much the same, except I'm now a star-san convert.
He seemed to like the taste of the coffee stout and didn't mention anything about it being sour. The butterbeer didn't get to be tasted though.
I feel pretty certain I used old Red Hook bottles (http://www.packworld.com/sites/defau...?itok=952QfxFe
), which don't have a lot of room in the neck for headspace. I usually fill to the brim, remove my wand, and bottle. There is a difference in headspace between that and longneck bottles.
That shouldn't be the difference between a slightly overcarbed beer and a bottle bomb though right?