Hey everyone! I'm glad you guys are enjoying this weapon. It's definitely unique and a ton of fun to use! However, there currently seems to be an issue with it's fire rate. I hit another thread with this so I'll quote it here for you all.
The Plasmatron fire rate appears to be a lot lower than intended. We're looking into getting this fixed. You can expect to see more shots once this is resolved. About 4.5ish for Shadow Shard and 5ish for Obsidian.