Lets look at the more interesting side of AR-18 serial number 057.
There are early features everywhere over here!
Of course like the other side you see no reinforcement at the front of the mag well. The most obvious difference is the lack of a dust cover. Early testing showed that there was just too much space for dirt and debris to get into the action. This was fixed during later production.
No curved charging handle on these early models, just like the AR-16 that proceeded it. To my understanding the spent cases would sometimes hit the charging handle and bounce back into the ejection port. To remedy this they changed the design to act somewhat like a shell deflector.
Reminds me a lot of the AR180B.
Other features that may not be so obvious, the reinforcing ribs in the upper extend all the way to the rear. They stop short on regular production models.
Finally we move onto the lower receiver. Compare the front of the trigger guard to the one in your gun safe.
(What do you mean you don’t have one?) (Go get one.) (You know you want to.)
On regular production models the front of the trigger guard serves double duty as a guide for the rear of the magazine. Not so on this example.
Let me know what you see that is different. There is at least one more thing that can be seen in the above photo. Can you spot it?