WW1 Enfield Muzzle Cover for Keeping out Trench Mud

Might be a bad thing if you forgot to uncover that if you shoot, which you can’t always trust the below 2.0 GPA, barely literate soldier to handle with.

It is with plastic covers. These were and are still issued in at least the US military. Quick and easy, and if you forget to remove it, it is just shoot through plastic.

Here's one affixed to a Sig rifle.

This same idea is used often with makeshift designs still. I made a post a while ago of people using condoms to do this.

Here's soldiers using used rocket shells for it:

Improvised methods typically cheaper and less likely to inhibit your ability to shoot. I've also seen hunters use painter's tape to do this.

In the US Marines, in boot camp they taught us to wrap the muzzle device in electrical tape to keep dirt out. I still do it if we are going to the field and we aren't shooting. I've never seen the plastic caps. If we had a built in cover like OPs picture, so many people would shoot right through them.