Personally, I dreaded the thought of chopping all those little raisins. I barely trust myself with carrots, never mind a raisin. So, I cheated.
I took a few handfuls of raisins and put them in my blender. Added about an equal amount of water, and ran them through. Chopped them quite nicely. They didn't turn in to pure "mush", but they were decidedly much smaller than when I started. I started adding more raisins, less water, etc experimenting until the texture was where I wanted. And I ran out of fresh water prior to getting them all chopped, so I used raisin water to puree raisins further. That was all in an effort to keep it right around a gallon total.
In retrospect, for my second gallon, I didn't worry about keeping it at a gallon. I put the whole gallon of water in there, and started it out in a big pot. Once the raisins started to settle, I racked the liquid in to a one gallon carboy - with no headspace like I had in the first batch.