It is common for a handgun shooter to find that lighter/faster bullets print lower on target than heavier/slower bullets, the usual explanation being that they spend less time in the barrel before getting past the muzzle, and so are less influenced by the rising point of aim during recoil.

But HOW MUCH difference there is, and just WHERE the POI is relative to the POA is variable with the shooter and their grip strength and technique, arm weight, body stance and (some claim) the phase of the moon, the location of Jupiter and the layout of tea leaves in the bottom of the cup.

The smart move when looking for the right ammo for a new gun is NOT to buy 2K rounds to start with and hope you guess right on the brand, bullet weight, bullet type, etc., but buy 50-100 rounds of a variety of different offerings and see what works best for your gun in your hands with your eyes and shooting style. If you start with a bulk buy and guess wrong (which is the statistically likely result), the few bucks you save at a local ammo sale will just end up being a much bigger waste of money.

When I got my Shield 9 I ordered both 124 and 147 grain ammo, both Speer and Federal and both their premium defense stuff and their FMJ blasting stuff. I was surprised to find that the 147 grain loads shot smaller groups and closer to POA than the lighter bullets, which is what I'd always shot before in my 9mm guns. That has also led to a continuing trek through a long list of 147 grain coated bullets from a variety of sources, looking for the right bullet for making my own blasting ammo. (Lead is cheap, usually gives higher velocity with less powder than jacketed, shoots just as clean, can be had in 0.355, 0.356 and 0.357 diameters, and it comes in COLORS - I'm thinking a green bullet would be good to use for the everyday loads, with red or blue if I want to load some rounds to a different spec.) If I hadn't experimented with factory ammo, I wouldn't have learned the benefit of 147 grain bullets. If I weren't experimenting with different lead bullets I wouldn't find what will work best for me, long run.

If you're willing to buy in the thousands, there are LOTS of online ammo sources that have very good prices pretty much all the time, on a huge variety of ammo you are very unlikely to see in a local store. (How many shops are likely to stock both the standard pressure AND +P Gold Dots - and in 50 round boxes, which sometimes can be found online for about the same price as 20 round boxes in stores and other, broad line, online sites?) You will almost certainly be a happier shooter, and probably money ahead, if you do your ammo "homework" first, before you place that big order.