I just got my dad and brothers into Mr. Beer but have never used it myself. They call me for tips while "brewing" and I recommended adding corn sugar vs. table sugar for bottling. Is the amount the same? You guys have done this?
Mr Beer is designed to make 2 gallons of beer... regular 5 gallons uses about 3/4 cup of corn sugar... if you scaled it, you should use around 0.3 cups.. If you have a balance, that should be around 1.6 oz.
Note that amount of carbonation (sugar) is a little different between different style of beers.
One thing that I like to do is make a priming solution... Don't put sugar into bottle or mr beer directly. It is hard to get consistent carbonation this way.
Instead, boil 1 1/2 cup of water, add the priming sugar, boil for 10 minutes.. Cool down to room temp, ~70F. Slowly pour it into Mr Beer Keg... gentle stir without splashing.. (sanitize the stirrer)..
With priming solution, you will get a more consistent carbonation.
In the past, I have used 1/2 cup corn sugar for priming.. It turns out pretty good.
Last note... Make sure your beer is completely fermented.. otherwise, you are having too much sugar which could be a beer bomb disaster.
I'd much rather spoon out 1/2 to 1 tsp. sugar into bottle than kick up sediment from the fermenter. I'd use a heaping half tsp. per bottle. The difference of sucrose and dextrose is probably within the margin of error. To get a bottle bomb you would have to bottle too early or put in three or more times too much sugar.
* table sugar is 5-9% more fermentable by weight; corn sugar has that amount of water content which increases weight but adds no fermentability.
* table sugar will take somewhat longer to carb up as the yeast cannot use sucrose directly, and deploy an enzyme (inverase, IIRC) to bust sucrose up into directly-consumable sugars (glucose, fructose).