I was working up loads in a S&W 25-2 45acp revolver with 45acp brass and no moon clips.

I was Lee factory crimping at 1.4" OAL, with 230 gr FMJ MOntana Gold, LIL'GUN powerder, and WLP primers.

At 18.9 the primer was completely top hatted.
That is a problem, as this gun is not stronger than the brass.

This morning I machined a clip on the lathe .050" thick that should hold the case back .022" from where it was.

I shot a 19.2 gr load [next in my work up series] and the primer is no longer top hatted.

What does it all mean?
I can't read a change in pressure from primers if the headspace is not constant.

I haven't gone over to look at Hodgdon's site for recommendations, but isn't Lil'Gun an odd powder for the .45 ACP? I'd thought of it as a magnum handgun and .22 Hornet powder. I'd never think of using, say, W296, H110 or 2400 in the .45 ACP, and I think they're comparable. And isn't that a lot of powder for the space in the .45 ACP case? I did try some of the old Speer manual Blue Dot loads in the .45 ACP back in the '70s, but they maxed out at 10.9 gr. (which was a bit compressed) under a 200 gr. Speer HP, and it only partially burned leaving lots of powder flakes. I'd stick with the faster burning powders and load the .45 ACP as a .45 ACP. Just my opinion, which I realize isn't what you asked for.

Most likely reason, your cases are a little short (every one I ever measured was) and without the moon clip it created excess headspace. Upon firing, the case was driven into the chamber by the firing pin, at ignition the case gripped the chamber walls and the primer (or section of it) began to expand rearward to compensate for the excess headspace. Cure-use clips with ACP cases. Only us AR without clips. Like NotRicochet said, you'll probably enjoy something like Titegroup, AA#5, 800X, Unique or Universal Clays much more than LilGun in that ACP.