Bottle Bomb Worries

I just gave out some cider in beer bottles as Christmas gifts and now I'm nervous. The cider was basically EdWort's Apfelwein recipe plus some blackstrap molasses, and it fermented out from 1.063 to 1.000 over a period of about 7 weeks. It tastes great, so I'm not worried about that. I'm just concerned that these bottles might be ticking time bombs.

I primed 5 gallons with 5 oz. of dextrose, and filled two (2) 64-oz. growlers (with plastic screw-tops) and about 36 12-oz. beer bottles. When I opened one of the growlers on Christmas Eve to make some wassail, it had already built up some serious pressure, and that was only about 2 days after bottling! The other growler was supposed to be for this Saturday, but the cap looks like it's going to blow off any minute now. I can vent that one no problem, but I'm worried about the 12-oz. bottles becoming glass grenades.

All the bottles have about 1" or 1.5" of headspace. My yeast was Lalvin Montpelier wine yeast. Am I worrying over nothing? Or do I need to tell everyone to open the bottles up pronto and/or crash cool them?

Sounds like it pretty well fermented out. It'll be fine.

That "pffft" sound is the gas that did not get absorbed back into the solution to carbonate it that's all.

Yeah, the math side of things looks good. At 1.000 there really couldn't be too much more fermentable sugar left in the cider. And the 5 oz of priming sugar can only produce so much CO2.

My main concern is that there was already some unknown amount of CO2 in the cider when I primed it. It was clearly effervescent as I racked it into the bottling bucket. With my beers, there is never really any CO2 in solution at that stage, and they always end up being optimally carbonated after 2-3 weeks in the bottles/kegs with 5 oz. priming sugar per 5 gallons.

I guess I should crack a bottle tonight and see what happens. I've been looking over Lalvin's spec sheet for the Montpelier yeast strain, and it looks like if worse comes to worst, I can just tell people to put the bottles in the fridge and the yeast will stop dead.

*edit* OK, I just sampled one of the cider bottles and all is well. The cider has just a hint of carbonation so things are going at the normal pace. The growler just happens to have a very flexible plastic cap that makes it look like the bottle is highly pressurized even when it's not.

FWIW, that little bit of blackstrap molasses seems to go a long way toward giving the cider a nice round flavor profile!