Fixed it for ya. You won't know what "customization" a rifle needs until you actually use it.
To that end, buy/build a carbine in it's basic configuration
http://i115.photobucket.com/albums/n...ine/PSA001.jpg
BCM offers good parts to assemble carbines with but I think the PSA rifle kits offer the best value. Again, get a basic carbine kit if you decide to build
http://palmettostatearmory.com/media...ssic_kit_1.jpg
Ammo Before Accessories. Shoot Before Customizing

