for “Example” I land at 3.5 grains of Bullseye and at 3.3 the slide funtion was 60 to 70% reliable would you bump it 3.7? in .2 grain increments.
I might, but I might not, it depends on many other factors. remember where you are, you're looking for something that is right on the bottom edge, or off "the map". And, when talking specific numbers (and small ones at that) they are useful in general terms, but not so much in a specific detailed application, without also taking into account other details (such as the gun) specific to your situation.
Simply put, I don't have your gun. My guns can be (and are) different from yours. My guns are different from each other. Minor differences, to be sure, but different. For example, my old Lyman manual lists 3.5gr Bullseye as the start load (124gr bullet) and vel as 900fps. A much newer Hornday book lists 3.9gr as the start load (115grfmj) for 1000fps.
In your situation, if you're getting reliable function from 3.5gr, I'd load a bunch of those and see if, in the amount of shooting you usually do between cleanings see if there is any change during the batch. Does the slide seem to get sluggish after 75rnds? 30? 150? no noticeable change? Maybe you don't need to bump the load up at all, you'll have to test that for yourself.
What I was trying to point out was that you might encounter the spot where things run fine, for a while, then start messing up, and to be aware that if you do, you'll need to bump the load up, just a bit, and then test again. Not that you will have to do that, only that you should be aware that you might have to.
And I would (and do) keep my COAL the same. I load for function and don't try to "adjust" the internal powder space with minor changes in seating depth.
For my 9mm and .38 Special plinking ammo, I've been loading Red Dot for years. Not because of any advantage that powder gives me, but because, for ME, its the most economical. Its economy for me wouldn't apply to you, because I still have about 1/3 of a keg of it, bought ages ago (so today, essentially free) and don't use it for anything else, anymore. Dirty as hell, but they do go bang just fine. I use it because I've got about 20,000 rnds worth of it, and other wise, its just sitting there.
Load and shoot at 3.5gr, if after a while the gun starts to choke, load the next batch just a tad more, and try again. If it works fine at 3.5, you're good to go.
Good luck. Be safe, have fun!