Bottle bombs...

So today I had 4 bottle bombs...no biggie, I get that its part of the hobby (although they were my 1L swing tops ).

The only thing is, the gravity at bottling was 1.012...I feel like that shouldn't happen. My first thought would be wrong priming solution mixture, but I used 2/3 c priming sugar for a 5 gal batch. Second thought would be not well mixed, but I thought I mixed this well.

Any thoughts?

Weigh your priming sugar with a small scale. Measure your volume of beer to be carbonated and use 1 oz. of sugar for 1 gallon of beer. This is just a base line measurement. You can add a few grams or take away a few depending on the style of beer your carbing.

So that was too much you think?

Bummer on the swing tops, those are pricey. What temp was the beer when you bottled? It has an effect on how much Co2 is retained from fermentation. Also was your gravity stable for a few days? I've had gravity in the 1.006 range at bottling on some simple beers mashed at lower temps (148) fermented with high attenuating yeasts (Notty). Maybe it just wasn't finished and the extra sugar just added some fuel to the fire?

temp was around 65...I'm sure the priming solution added a degree or 2. Gravity was stable for 5 days leading up. My only guess is that the yeast found some sugars and got back to work.