If you're looking for a Back 4 Blood drop attachments option or a button to pull a certain silencer or muzzle off your gun, you're one of many. Players in Back 4 Blood have found that the ability to take attachments off their weapon doesn't seem to be present, despite being a fairly obvious feature that any experienced cleaner would want.
For that reason, we'll explain properly if you can drop attachments in Back 4 Blood, what the limitations are, and what's likely to change in the near future around this feature.
Can you drop attachments in Back 4 Blood?
No, at time of writing there is no Back 4 Blood drop weapons option, feature or button for you to use, despite the fact that it feels like a very obvious thing to include. Once an attachment has been put into an empty slot on your weapon, the only way to get rid of it is to find a replacement attachment, apparently because rifle maintenance works under the custom of "dead men's boots".
So to explain: let's say you have a Vector, one of the Back 4 Blood best weapons around (no matter what anybody tells you), and there's nothing in its optics attachment slot. Then you find, pick up and attach a high-zoom sight into that slot. Not exactly what a short-range gun like this needs, but the problem is that it's locked in place until you can find another different kind of scope to swap it out for. When you pick up that new one, the high-zoom sight automatically detaches and falls to the ground for somebody else to pick up if they want it. However, until that point you can't detach the high-zoom sight in any way whatsoever; you have to get a replacement optic for it.
Can you swap attachments between weapons in Back 4 Blood?
No, unless you use the principle outlined above, there's no way to transfer weapon attachments from one gun to another without a third loose attachment to act as an intermediary, turning the whole thing into a horrific fox/chicken/corn riddle.
So if you find a purple gun with no attachments, but you're holding a green one with lots of high-quality attachments you want to keep, you're basically stuck unless there happens to be several unused attachments of each type lying nearby that you can use to pry them out of the first gun. It's as "simple" as that.
We don't know if the option to swap attachments or drop them will be added by developer Turtle Rock Studios in the future, as to our knowledge no comment or statement has been made either way. It's possible that the developers would prefer to leave it as is, so as to prompt difficult mid-campaign decisions, or perhaps it'll be changed in the future for player friendliness. Either way, we'll update this guide accordingly.