At Just Airsoft Guns we stock both internal parts and body parts – plus a number of potential upgrades that can keep you and your airsoft guns competitive. Some of the easiest-to-fit upgrade parts are stocks, flash hiders, and front grips. Springs are one of the most popular due to the need to manage the FPS of your airsoft guns. An example of an upgrade that can be complicated to fit is changing a standard M4A1 to a RIS M4 – this can be difficult and in some cases very challenging, but great as a project you can brag about. Don’t forget – making internal changes to your airsoft gun will void your warranty.