Afaik the A1E1 (or Model 645) was a transitional prototype for what would become the M16A2 and from what I've read it calls for a glued-on brass deflector which the ingame model lacks. And I'm not sure if the sights and upper receivers. And from the images I've seen these had A2 rear sights adjustable for elevation and windage while the in-game model has A1 sights/upper receiver though I could be mistaken. I believe a more suitable rifle would be M16A1s.