Bottle carb measurement

Having an issue here.

AHS gives you a 4.5 oz bag of bottling sugar. NB is 5 oz.
The "standard" Briess bag is 5 oz. The temp in my house is fairly constant but sometimes the 5 oz is flat. Sometimes the 5 oz is a bomb.

I have seen the charts using the maximum temp of the uncarbed beer to estimate the # of volumes and how much of the different sugars to add... but .... it doesn't seem to work very well.

Is there a trick - a way to know for sure. I'm tired of alternating between flat beers and gushers.

I should add that I tend to brew often and therefore do long primaries and secondaries. I am not bottling at much above 1.015 so residual sugar is not an issue.

Batch 48 - Celeia IPA from AHS was flat with 5 oz
Batch 49 - AHS Golden Palisade Ale was just right at 5 oz.
Batch 50 - a home recipe APA was way foamy at 5 oz. One bottle exploded
Batch 51 - AHS Cream Ale is way foamy at 5 oz

For your flat beers you may have crossed the line of too long of a primary/secondary. The longer you let it settle and yeast fall out of suspension the fewer you get into your bottles. The few starting yeast in the bottle the longer it would take for them to consume all the sugar and carb up the beer.

As for the bottle bombs it's hard to say. I have gone round and round with folks about bottle conditioning temperatures and it's effects. However the majority of them will say one of two things; 1.You bottled too soon or 2. Your sanitation is off and you have "bad germs" making extra CO2.

There is really no trick to it per say. There is still an amount of guessing going on with the quantity of yeast in the bottle. Time might be your friend in this case, let the flat ones set another few weeks to see if they catch up. Standardizing the brew schedule might help also, such as every brew gets the same amount of fermentation time. The only other thing is make the next step by taking the yeast out of the equation and start to keg.

Build yourself one of these and you'll be able to see what the pressures inside a batch of bottles is doing. Use a 50# or higher range gauge. 30# is not enough. Just fill the test bottle as you would a regular bottle when you do the batch.