This is a DoRA, not your typically made LoRA. A1111 v1.9.0 and up is required to use this. Forge users must download two files, which can be found here. Go to stable-diffusion-webui\ldm_patched\modules and replace the files there.
Weight: 1.0
Trigger + Additional Tags: gun to head, holding weapon, holding gun
The results of your generations are dependent on the additional LoRAs, weights, and models you use, so it may not work or come out as consistent as my sample images.