Without seeing a crash log it wont be easy to help. But I suspect it is the same issue I used to have when using it. Used to get these occasional crashes that were linked to the rendering of this little "poof" animation it does once it fires the charge. It was very random how many times I crashed from it. Some times it could go weeks between, other times several times per day. Don't think I ever figured out what caused it. Maybe a Optifine issue? Dunno, it was way back in Unleashed.
If you are in singleplayer you can disable rain completely by hitting E, click Options down bottom left, Inventory. Change "Recipe mode" to "Cheat mode"(might have to hit Global and then toggle the W). The exit and in the inventory you now have a raindrop icon up top left. Left click will toggle rain on and off. Right click it will turn off rain completely for the duration of the world. Follow the above steps and turn it back onto Recipe mode again.