balancing an O/U can be a tricky thing.. especially if we're talking a competition gun... theres a lot more going on than just adding or subtracting some weight to get things right... where the gun balances FOR YOU is as important as how much the gun actually weighs).. how you look down the rib pre and post changes to the gun matters, etc..etc..
for example.. on one of my daughters comp guns (30" bbls).. we needed the LOP reduced by about .75".. doing this moved the balance point about 1" in front of the hinge pin..
but.. screw in a pair of extended chokes.. and the balance point moved back about .5"..
so then it was a matter of figuring out how much weight (not much.. only a couple of oz) to place in the stock, to get the balance point back where it belongs (for her stance, mount, etc the best place is to have it balanced right on the hinge pin of this particular gun)..
You'd be amazed how little weight it takes to move the balance point.. and how much of a difference the placement of that little bit of weight makes..
For me, I like the balance point to be a little forward of the hinge pin.. I have long arms (6'4" tall.. and the arms that go with a frame like that)... when mounting the gun, I tend to push my non firing hand far forward on the forearm.. even on a longer barreled gun (32") the balance point typically isnt forward enough for me.. If Im going to add an OZ or two of weight its usually going to be in the forearm..
Honestly I find it best to either just leave a gun alone (shoot it as it comes from the factory).. or.. take it to a professional stock fitter.. they will be able to figure out how to properly adjust the LOP, then move the balance for you, adjust the comb, etc.. so that you get maximum effectiveness out of the gun.. Its not nearly as expensive of an exercise as you would think (we've got a guy in North DFW thats done fittings for hundreds of the kids that are involved in the HS competition circuit that does great work, has a super fast turn around time, and is super affordable (I paid less than $150 to have my wifes new Berretta fitted and have a new recoil paid installed just last week)....