Glock 43 (9mm). It's a tiny sub compact, 3.5" barrel ... light soft shooting fun load for playing around and an occasional IDPA bug match ... 100 power factor ... 231 ... decided to go with 147 instead.
With 147 gr bullet, to produce 100 power factor, you need higher than 680 fps.
My soft shooting 9mm reference load is 147 gr bullet with 3.5 gr of W231/HP-38, which cycles all different pistols I have used and is pretty accurate load -
https://www.thehighroad.org/index.php?threads/9mm-147-gr-lead-bullet-powder-comparison.748940/
Here are available W231 load data I found for 147 gr bullet:
- 147 gr Hornady XTP W231 COL 1.100" Start 3.0 gr (755 fps) - Max 3.4 gr (845 fps) - http://www.hodgdonreloading.com/data/pistol
- 147 gr Speer TMJ W231 OAL 1.115" Start 3.5 gr (855 fps) - Max 4.1 gr (957 fps) - Lyman #49
If you want to go below 3.5 gr with W231/HP-38, how low you could go will depend on the recoil spring rate of Glock 43. Knowing the stiffer recoil spring rate of my Shield 9mm (subcompact with 3.1" barrel), my guess is not too far below 3.5 gr to reliably cycle your Glock 43 recoil spring. Perhaps you could go down to 3.3 gr, maybe 3.2 gr and still reliably cycle the slide.
So "work down" (Instead of work up) from 3.5 gr and test 3.4, 3.3 and 3.2 gr to see which charge reliably cycles the slide and still maintain acceptable level of accuracy, especially if you want to shoot IDPA matches.
Another thing to consider when going below published start charge is efficiency of powder burn and consistency of chamber pressures which translates to accuracy.
To me, W231/HP-38 is the reference powder that separates faster burning powders and slower burning powders -
https://www.thehighroad.org/index.php?threads/powder-shape-and-burn-rate.852012/
To load lighter than W231/HP-38 start charges while still maintaining efficient powder burn for consistent chamber pressures to produce accuracy, you would need to use faster burning powders.
In my 147 gr powder comparison thread, I used 3.5 gr of W231/HP-38 as reference benchmark with felt recoil number of (5) with (10) being equivalent to factory Winchester white box. 3.1-3.3 gr of fast burning Promo (Same as Red Dot burn rate) produced lighter felt recoil of (4) but needed to use 3.3-3.5 of Promo with felt recoil of (5) to equal accuracy of 3.5 gr of W231/HP-38 load.
2.7 gr of Bullseye produced very light felt recoil (3) while still reliably cycling the slide and produced comparable accuracy to 3.5 gr W231/HP-38 load. So Bullseye would be my choice to produce lightest felt recoil load that would still reliably cycle the slide and produce accuracy.
With Titegroup which burns "relatively" slower than Red Dot/Promo and Bullseye (But faster than W231/HP-38), 3.1 gr produced comparable felt recoil (5) and accuracy load as 3.5 gr of W231/HP-38. Yes, I do like "hot and violent" burning Titegroup for 9mm as it produces more accurate loads than W231/HP-38 for me.
