Well I found a load and case length that seems to work pretty well. I trimmed about 270 .38 special cases down to 0.860". Mainly because that was the shortest my trimmer would go. And it wasn't that much of a pain to trim either, I hooked my trimmer up to my cordless drill and was able to trim one per 10-15 seconds. Between screwing around trying to set up the drill and finding a way that was fast and worked well the trimming operation took me about 2 hours total.
I tested different cases and I found that only brass that was headstamped Winchester or Federal was thin enough near the case head to reliably accept a 0.357" bullet without bulging so much it wouldn't fit the chamber. Aguila and PPU brass was the thickest and bulged the most. RP and W-W brass was in between. Brass with a headstamp of "CBC" was also in between thickness, but it wouldn't trim properly and mostly just crumbled while I was trimming it, like it was made of compressed powder or something. I don't know who makes CBC brass but it seems pretty low quality.
Throughout this I used 125gr LFP bullets. I originally tried to use 2.4 grains of Win 231, because its what I had on hand, but was getting FPS readings very low and inconsistent and had a LOT of unburned powder left over. The absolute lowest FPS reading I got was 151 fps with 2.2gr of Win 231 and an OAL of 1.118". I decided the powder was the issue so I ran to the store to get some Titegroup. After some testing I settled on a load:
1.9gr Titegroup, OAL 1.093", 125gr cast LFP bullets, CCI 500 primers with medium crimp.
Results in fps:
527
496
486
524 Average: 509 fps
526 Standard Deviation: 14
512 Spread: 41
508
511
517
489
I even managed to set up my chronograph so i could point the gun straight down and fire and the variation was minimal still:
442
439
456
This load is more consistent, lower power, and way more accurate than my low velocity .38 special load, so I'm content with it. Also, since this is technically a "wildcat", I need a name for it. I was thinking ".38 Wimpy"?