I've tested several after-market triggers for the AR-15, and I desided to go with the JP hammer & trigger. The hammer is very light weight, and it will noticably speed up your lock time. This makes it easier to shoot well, especially from the offhand position. The JP trigger (the trigger itself) is quite time consuming to install correctly, and it must be installed by someone with a great deal of patience to get the most from it. When using the JP trigger and JP hammer, I can always get the trigger to 3 pounds, and it's as crisp as any trigger you ever saw. However, I don't recommend using the JP hammer spring ( or ANY weaker hammer spring), because the primer hit becomes too light to provide good accuracy. In fact, I always use the heaviest hammer spring I can find when installing the JP trigger parts.
Anyone can lighten the AR-15 trigger by installing a weak hammer spring, but I bet you'll notice a loss of accuracy due to poor ignition.