Some of the guns in Borderlands have a burst fire count. What does that mean? For example, Sledge's Shotgun:
The Legend Lives, Sledge's Shotgun: Knocks back target several feet and 10000% burst fire count
Refers to how many rounds it fires, and possibly also how quickly it fires them. A quick search turned up this post: +burst fire count.
Basically, Burst fire is how many shots it fires off in the span of a normal shot. So a gun that shoots 1 round a second would be 1.0 ROF, but if it was burst +100% it would shoot 2 every second. A burst fire pistol with a +500% will shoot 6 rounds in the time it would normally shoot 1. So... 1 trigger squeeze = 6 bullets. The 10,000% on Sledge's shotgun just makes the rounds almost instintanious, since it's only a 2 round gun. Basically double barrel.