Pistol caliber carbines such as 9mm, .40 S&W, .45 ACP, and 10mm are a blast to shoot but can be tough on AR-15's internal components. Without a properly tuned blowback system, you run the risk of being overly destructive on internal lower parts. Running a blowback AR15 with a suppressor can further increase the risk for damage. In addition to a properly weighted buffer, the KVP Extra Power recoil spring is a must! The KVP XP 17-4 SS spring offers increase pre-load over standard springs. The additional preload helps increase the Blowback systems dwell time.
The KVP 17-4 SS Pistol Caliber Carbine XP Spring is proudly MADE IN THE USA by hard working American men and women.
It's an upgrade option. Not required, and it's up to personal preference. They do come installed/assembled into our Side Charging C9 and C5 pistols and rifles.
You can use a standard spring and 8 oz buffer, but this spring would definitely improve recoil management and smooth out the operation of the gun.