I just weighed a cup of corn sugar in my brewroom and got 4.5 oz. The OP added more to get closer to the 7 oz.
I would recommend caution when carbonating over 3 volumes in bottles. Its better to be a little low than high. If you over-carbonate or have a bottle that's a little weak, you may experience a bottle bomb as you mentioned.
It happened once to me even though I thought I was being cautious. That's one reason I prefer to keg these days.
After that, I stored them in an enclosed area, to prevent damage from flying glass chards. From your description, I would be concerned about this.