OK, I am glad some of you can simply say go to the gym and carry the rifle you have, but it goes much further then that. I workout everyday (cross training, weight lifting, and running) and thought the Stag was heavy as well. You also have to take in body type, arm length, etc into account. I am 5'8" and do not have long arms. So for me to reach out towards the end of the forarm on the Stag 3g put me in an awakward shooting position. If I moved my hand back the rifle felt unbalanced and I could not stop the rifle as fast when i was quickly transitioning from target to target.
I quickly realized a 16 inch gun or an 18 inch lightweight gun would have to be the ticket for me. I have been running my work rifle (S&W midlength magpul) in local three gun matches and have been winning. When doing different drills (even at a distance) I found the heavier Stag not to handle as well for me.
So for an individual to simply say, "work out" is possibly not getting to the actual problem of why that certain individual thinks the rifle is heavy.
Adam