Production division will allow you to add up to two ounces to the weight of your unloaded gun. While you can add that weight anywhere, it makes a lot of sense to add that weight to the front of the gun--the idea being to dampen muzzle rise. In addition to adding weight, a reduction in recoil spring tension will keep the muzzle from being driven downward when moving back into battery. So, after some considerable research and contemplation, I bought a tungsten guide rod and 13lb recoil spring for my M&P 9 Pro.
The guide rod I ordered was supposed to weigh in at 608 grains (400 grains is one ounce), and I didn't know at that point what the new ISMI flat wire spring weighed. Before I ordered, I weighed my stock captive unit to see just how much weight I would be buying. I found the stock unit to weigh 389 grains. Looking at a prospective gain of only three quarters of an ounce, I had my reservations when spending my $60.
So in total, we're at 893 grains, or one and one quarter ounce more than the factory unit. Very well, but what does that mean on the range?
I had been thinking, dreaming really, about shrinking my split times, which are stuck around .19 seconds (Jerry Miculek, PBUH, can pull the trigger on his revolver every .125 seconds). So the first thing I did, well, after a few rounds to make sure the new rig was safe, was to record some splits on my shot timer. And they were.....exactly the same. But recoil was definitely flatter than before.
The price of that flatness is a little more felt recoil, but the payoff is actually immense. Though my best split time of .19 (I actually saw a .13, but I was just going nuts and not hitting anything) would equate to one A hit and one C hit. I can now ding an 8" plate at 10 yards in that same .19 seconds. So although my time is the same, my hits would be two As, for an extra four points per target. Those few points, over an entire match, can move your name up significantly.
And that brings me to my next point. No amount of gear can push your name up the list on its own. If you're already doing ok, gear can give you an edge, but you still have to do your part. Before you dump money down the gear money pit, make sure you're practicing and that you'll actually be able to take advantage of whatever you're buying.