[PC][2000-5] A shooter like Half-life

I’ve been trying to remember and find a game that I used to play on pc, I can only remember little details but I remember you only had one gun but it was a sniper, shotgun and a AR in one and the barrels would spin around. You fought giant scorpion like creatures. Hopefully I’m remembering the details correctly. It’s the one game from my childhood that I can’t find