Probably the best buffer system you can get. - Geissele Premium Mil-Spec Buffer Tube Assembly With Super 42, H1

The spring that comes with this is the most robust spring system on the market. The dual coiled design is a step above your standard spring and has an extra premium feel to it. The only downside to the Giessele spring/ buffer is that H1 is the lightest option. There is no standard weight available, and the instructions say not to use any other brand of buffer with then spring.