Others might have different views regarding bottle bombs, but I used the Brewer's Friend calculator earlier this year in Autumn (our seasons are 6 months out of step with yours) to add 6g of sugar per litre (about 6 tsp per gallon) for a theoretical 2.0 - 2.5 vols of CO2 in 500ml (1 pint) bottles.
I had several batches of 4.5 litres (a gallon) spread over about a month. They each were left for a couple of weeks in Primary then racked to Secondary for about a month to six weeks. With the earlier batches, the sugar (about a teaspoon) was added to the bottles, but with later batches it was added and mixed to the bottling bucket. So, I don't really know what CO2 vol I ended up with in each of the earlier bottles but I am drinking them now with no sign of bottle bombs and a nice "mouthfeel" from the carbonation. Various "authorities" suggest anything up to 2.5 tsp per litre as a carbonation "rule of thumb". After bottling, the cider has been sitting in our "cool store" at 40-60 degrees F over winter.
Unfortunately I wasn't smart enough to measure the SG after adding the sugar so I don't know how much sugar I really had to convert to CO2 (still learning!!). I am guessing I bottled with something like SG 1.005+. I am planning to experiment with my own concentrate next year and add this to bottle carbonate instead of adding sugar, in order to have a few more "apple flavour molecules". The juice OG before fermentation was between 1.050 and 1.070 depending on the mix of apples (we juice our own) and had a FG of 1.000 - 1.004 for different yeasts (Safecider, Nottingham, and EC1118). They all taste great!
