[Nick_C_S]

so I figure I can start lower than 5.1 gr of #2.

You can indeed.

What you are - in essence - doing, is a load "workdown," as opposed to a load workup.

And like a load workup, you should at least start with published data. In this case 5.1 grains.

From there, you can move down in 0.2gn increments or whatever. The concern here is a stuck bullet; so make sure you're seeing your projectile impact the target, or the berm behind, etc. I recommend a chronograph for testing these. For me, with lead bullets, I start getting nervy of the possibility of a stuck bullet when velocities drop below 600 f/s (700 f/s for plated or jacketed).

I load a lot of 200 LSWC's. And I have a Colt 1911 with a lighter recoil spring (12#) that only shoots lightly loaded 200 LSWC's these days (I use the ultra-fast AA Nitro-100 @ 650 f/s for these).

I have loaded with AA#2 quite a bit (great stuff). But I was surprised to check my load data just now to find I have never loaded 200 LSWC's with AA#2. So I have no personal experience data for you

Speaking of AA#2: It'll definitely work for your application. But I will say that is it has a bit of "slowness" to it for a fast propellant. As mentioned above, I haven't loaded with it for 45 ACP. But I have tested it extensively with low-power target ammo in 38 Special. If it behaves in 45 like it does in 38 (and I suspect it will), you'll find a good deal of chartreuse colored grainy propellant by-product left behind. It's not a big deal, unless it bothers you to know it's not running at optimum. What is really spectacular is how consistent my results were while it was running in this low-pressure non-optimum condition. Like I said, AA#2 is great stuff - even when it's not running at optimum.