Hi Forrestcook,
The builder is designed to try to prevent any incompatibilities that may exist between various parts. So, for example if you had an 18 barrel that had an integrated front sight or crowned muzzle, you couldn’t add a flash hider to it. It’s not perfect, but we try to avoid any situations that may require special gunsmithing.
Another good example is if you are using a complete lower, you couldn’t add a pistol grip or customized accessory to it. It will just replace the lower. We know that physically, you can do those things fairly easily, but it makes it more challenging to be user-friendly on the builder. We’re working on a way so that it warns you of incompatibilities instead of just replacing the item. Currently that works when you try adding the wrong size of handguard to a barrel.
Thank you so much for the feedback. There are billions of scenarios out there we try duplicating. If you run across anything you feel could be a mistake, please send us the stock number or product titles you are using so we can fix it.
Brownells