Hi.I want to develope a game.Now,if i modeled lets say a Colt m1911 can i call it that in-game?Can i put the original markings on the model?Also,the game should feature a very in-depth weapon modding mechanic.Can i just use the real components of the gun like an exact model of the whole gun mechanics?

p.s. sorry for bad english,i am german.

You can't use weapons that have active patents, copyrights or trademarks on it.

There are firearms that have no patents or any kind of trademark and some firearms have a patent for the inner workings but not the look of the gun.  However most patents cover both the look and innerworkings and as such can't be used in games without the permissions of it's IP owners.

Some manufacturers like Remington also place patents and trademarks on parts of there weapons. As a example: 

https://www.remington.com/rifles/bolt-action/model-700/model-700-pcr Every piece of the 700 PCR is in fact protected by law, from the grip to the bolt. So if you copy even a part of it you are at risk of legal action.

At the moment large game publishers, like EA, are actually pushing for these laws to no longer apply to games, but for now it's a gray area.

There are lawyers who specialize in researching these patents and trademarks for developers; they can even help you get in contact with the manufacturers of the guns.

There are fair use laws but getting advice from a lawyer on this is recommended.

If you can't afford legal help then design your own guns.