If you read all of the comments and replies at the bottom of the list, you will see some important information. One thing to note is that Silencershop tested the adapters based on their ability to make contact with and be timed to the shoulder of the barrel. There are some suppressor adapters that are made to make contact with the muzzle face and be timed off of the contact with the muzzle face. some older Surefire adapters were made this way. Also, the adapter from AAC for their SCAR-H SD was this way. I appreciate Silencershop's efforts to do this. I wish suppressor companies would the same thing for us.