Stock length and cheek weld and good shooting
There is more to a Carbine stock than just adjustability and length of pull. Body armor can make your standard Carbine feel really uncomfortable and put on a tactical vest and you’re probable a good 2 inches or more shorter on your Carbine stock. One other thing that comes into play is the amount of play you might end up with if you have a commercial stock sitting on a Mil-spec buffer tube.
Knowing something about your Carbines parts history and if its all Mil-spec is going to be very important if you start to accessorize your parts. Magpul accessories give you a lot of options for making your AR15 fit you right and adjust to the gear you may be using. The Magpul MOE stocks and accessories are also something very new and original to consider.