Go to the equipement => Armory => pistols => select a pistol => Select a type of attachement in the Attachement tab at the right. ( suppressors, sights, bipods ). And now select a new pistol. As you can see we can now see if we are in the Suppressors Attachements "Suppressor I" to "Suppressor V". If you want to check the sights and comebacK. You will get the message "No compatible attachements available".

If you need a video to understand what I mean just tell me.