I’m trying to get the Lock and Load Trophy (“Fully equip a level 5 weapon with level 5 mods.”) using a .44 Magnus but it hasn’t popped yet.
I’ve got a gold Magnus and I gave it a gold 2-4x scope and a gold suppressor, but no trophy. Do I need a weapon that can take magazine attachments as well?
I think you do have to get all possible attachments equipped.
I guess that makes sense. It’s weird though, PSNProfiles is a site I use a lot when I’m trophy hunting, and they said that you didn’t need every attachment slot and you could do it with one of the shotguns. 
I am not saying that they are wrong, because I don’t know. I only remember that I did it with all 5 attachments slots, because I thought that was meant.
Just popped the trophy after putting a 5c red dot, 5c magazine and 3c suppressor on a 5c MP5. Guess you just need to fill all the attachment slots with anything.