I'm perplexed. I've recently started shooting about six inches low at 25 yards. It happens whether I have the arched or flat mainspring installed. I aim using the Navy Hold in the Weaver stance and shooting 230 ball. I'm shooting nice groups, but they are just low. I had another guy at the range shoot the gun and he shot dead-on at the same distance. This only happens with this gun. I shoot my Sig 226 and my Glock 17 perfectly. Am I flinching downward? Please help.