When I am bottling my beers I tend to do so into 22oz bottles and usually have enough remainder to make one 12oz. I was wondering if it would be safe to bottle the remainder into 8oz or smaller bottles to open one at a time up to taste how the beer has aged/bottled? Could this potentially be a bottle bomb? Where can I get small bottles that I can cap and what is the smallest I can find?
While I have seen small glass bottles akin to flasks in shape and size at my local homebrew store, I cannot seem to find anything similar online. With more digging, I'm certain they could be found, but I'm at least positive that there are bottles smaller than 12 oz. that could be used.
So long as your priming sugar is evenly mixed in the solution before bottling, and the amount of air space remaining in the bottle before capping is proportional between the bottle sizes, no matter the size of the bottle, they will all theoretically carbonate to the same levels, in the same amount of time. So for instance, if you filled a 22 oz bottle 7/8 of the way with beer, leaving 1/8 open air, and you filled a 12 oz bottle 3/4 full, leaving 1/4 of it to open air, it would carbonate differently between the two bottles, in both amounts of CO2 dissolved in solution, as well as time it takes to carbonate. In the above example, the 12 oz bottle with 1/4 of the bottle being air, it would carbonate slower, and have less CO2 in solution (as well as potentially more oxygen in it to produce off flavors).
Chances are, unless you have large differences in your bottles when filling them across 22 oz, 12 oz, and potentially 8 oz if they can be found, you probably won't notice the difference in carbonation between them. Just make sure they all relatively share a similar ratio of beer:air in each bottle (determined by eyesight), they'll all carbonate the same, in the same amount of time.
Which means, you mentioned:
open one at a time up to taste how the beer has aged/bottled
Your smaller bottles you intend to taste over time will carbonate just as quickly as the 12 oz and 22 oz bottles.
Long story short, you won't have bottle bombs, while I cannot find any bottles smaller than 12 oz, I'm certain they are out there, and as long as you keep the bottles proportionally similar in the beer-to-bottle-size ratio, they'll all carbonate in the same amount of time, to the same levels of carbonation.
Rogue Brewing was, at least for a time, bottling their higher-gravity beers in 7 oz. brown glass bottles. I've re-used them for homebrew with the same crown caps as I use on other bottles.
So at the very least this size of bottle does exist, but I don't have suggestions on how you can source them.
Scott provides a good answer on mixing your priming sugar to avoid bottle bombs.