In my World of Dragons modpack at https://www.curseforge.com/minecraft/modpacks/world-of-dragons/

I have these mods installed:

• Techguns 1.12.2-2.0.2.0_pre3.1
• Mine and Slash 1.12.2-1.9.3
• MS Auto-Compat 1.12.2-1.0.7

I've talked with AzureDoom which is on the Mine and Slash team and the author of MS Auto Compat which interfaces other mods' weapons to Mine & Slash.

There is an issue where your weapons do not hurt non-techgun mobs and players (probably for the same reason). The problem as described by them is that your mod uses custom projectiles that don't inherit from the Mojang project classes and as such they can't correctly scale the projectile so they nullify it instead when it is applied against a mob not from your mod.

The M&S team have informed me they are not patching their mod unless it causes crashes as they've moved deep into 1.15.2.