I made NB's all-grain chocolate stout in the fall. I added some additional pale ale malt, some baker's chocolate at the end of the boil and racked over the cocoa nibs sitting in vanilla vodka. I also added 7 oz. of organic cold pressed mocha coffee to secondary as well. I mashed around 155 purposely to yield a sweeter stout. The kit comes with lactose which I am well aware is non-fermentable. My o.g. on brew day was 1.072. I used 2 rehydrated packs of 04 on brew day which was Nov. 7, 2018. On Dec. 2, 2018 I bottled up 45 of them using just over 1/4 cup of priming sugar as I have had gushers with stouts in the past. My gravity at that time was 1.030 after the gravity had stayed at that reading for three days. I knew it was high, but I figured with the higher mash temp + lactose that was reasonable. On 12/8/18 there was a hint of carbonation in the beers and on 12/13/18 it was the ideal amount. Yesterday, they were gushers. I just tried 2 more bottles this morning and they too gushed. I tested the gravity and it was now 1.010 so something happened in the bottle between bottling day and brew day. This only happened with the stout. I have bottled three other batches - a porter, a gingerbread brown and a wheat beer since bottling the stout and none of them have had this problem. Any ideas? I've had similar problems with gushing stouts in the past. Again - my gravity was stable for three days prior to bottling and I used considerably LESS priming sugar than priming sugar calculators indicate for fear of gushing.