Found the sweet spot! Vit C for 100% whole grain, coarse, home-milled.
On my 6th loaf since joining TFL (7th overall "bake" since joining), I finally found the "sweet spot" for using home-milled, near 100% whole grain flour, and a sourdough starter (Carl's 1847 Oregon Trail).
It was 86.3% overall hydration, 14% percent prefermented flour (flour in the levain divided by overall flour), and 1/4 of a 500 mg vitamin C tablet. (I could probably go lower on the vitamin C, but 1/4 tab was easy to do.)
That Vit C really made a difference, giving a good balance of extensibility to elasticity of the dough. And allowed that to occur at a lower hydration so that it did not take too much time to bake off the moisture.
I credit the Loafers in general, and DanAyo in particular, in encouraging me to precisely measure and record hydration, to use 14% prefermented flour, and to try out vitamin C.
452 g Prairie Gold, HWSW, home-milled coarse.
134 g Kamut khorasan wheat, home-milled coarse. (586 g flour so far.)
1/4 of a 500 mg vitamin C tablet.
473 g water.
Autolyse, then Add 190 g Levain, at 100% hydration. Levain is mish-mash of BRM dark rye, BRM WW pastry flour, PG, Kamut, white rice flour, and about 1 tsp each of BRM 1-to-1 GF flour, maltodextrin, dextrose, and dried malt extract. I was running late on building up the starter into a fresh levain, so I added the sugars to hurry things along.
Flour so far: 586 + 95 = 681 g.
Water so far: 473 + 95 = 568 g.
Added/folded in 13.3 g salt (1.95%) semi-dissolved in 20 g water.
Final hydration: (568 + 20) / 681 = 86.3%.
Final weight: 588 + 681 + 13 = 1282 g = 2.82 pounds.
Not a big oven spring, not an impressive bursting score line, but it finished baking in 74 minutes, ten minutes quicker than previous bakes, probably because of less water to cook off.
I'm still going to have to experiment with autolyse, bulk ferment, and final proof times, in order to get better oven spring.
More importantly, the crumb, while not Instagram-worthy, was still light and airy enough, that a non-baker would not guess that it was home-milled near 100% whole-grain.
I've also concluded that Kamut doesn't mix well with hard white spring wheat, in terms of taste. So I'm going to try mixing in some hard red spring wheat, instead of Kamut, for flavor. And then try a separate loaf of 100% Kamut. I do like Kamut for flat breads, which durum is known for. Kamut is very very close to durum, genetically, and in baking characteristics.