Some of the mods are locked, but some aren't. The difference in appearance, damage, etc. is incredible. They even SOUND different. Think how fearsome guns sounded in Red Dead Redemption. It's like that. I'm only a little bit in, and I've invested several hundred thousand dollars into each gun... Barrels, muzzles, liveries, etchings, camo, tracer rounds, armor-piercing rounds, full metal jackets. It is insane.
Mod-able weapons so far:
- Assault Rifle
- Combat Machine Gun
- Heavy Sniper
- Sub-machine gun
- Revert (For when you wanna go back to your mk1 weapon)
I had to log off and go to work, so I couldn't get all the details I wanted, so this thread is a work in progress. Please feel free to contribute any knowledge and experiences. That said, I was on the fence prior to this DLC dropping, but the gunplay looks to be seriously changed.