1. Try different ammo.
2. Make sure nothing's binding in the gun.
3. Make sure the gas key isn't loose.
4. Make sure the gas ports in the barrel and gas block are aligned.
5. Post more detail about the gun; parts, who assembled, etc.
With all respect toTripHlx, clipping the buffer spring, while a relatively safe/inexpensive thing to do, will cause other issues. Cutting a spring INCREASES its rate. While you'll have less pre-load, by the end of the carrier's stroke, the spring will be exerting more force than the unaltered spring. So it probably won't fix your problem. (The higher rate also puts more stress on the spring, increasing the likelihood that it will break.)