Shutter in bulb mode

I used shutter in bulb mode for taking pictures of fireworks, and it took about 3 seconds after each photo taken before the camera was ready for a new one. It seems too slow to me and I wonder if it can be quicker?

Those are great shots! The speed could get better with a bigger, faster memory card.

I'm using Duracell 16 gig class 10. I think it's fast enough.
Some background information: D7000 with 18-105mm lense, manual mode, f/8, bulb shutter with tripod, ISO 100
I found that framing was the most difficult part, and some times I had to release the shutter earlier to avoid the entire picture being over-exposed.