As noted in post # 13 above, I rubber-banded two pieces of Walnut scrap together and glued with Titebond III. It's 27 hours later (instructions say fully cured at 24 hrs) and time to test the join.
First pic below shows the pieces clamped in my mill vise. I pulled back as hard as I could with both hands/arms, and could
not break the join. I could see the Walnut bend a bit, but it wouldn't break. This is great! The joins I envision making are non-load bearing joins, so this would work OK.
I still wondered how strong the join was, whether the wood would break, whether the wood fibers would rip out before the glue let go. So, I put a 12" Crescent wrench on the upper piece, and gave it a go. The glue join finally broke; no fibers ripped out; no wood breaking (second pic).
Still not a failure. I won't be yanking on these joins on the rifle. The only negative I had was when it came time to clean off the surfaces. The glue itself would not sand cleanly; it was semi-flexible and 'peeled' rather than sanded off. That could be a problem when sanding down the join or using it as filler.
After digging that DevCon 2-Ton Epoxy out, I decided to try that, just for S&G. I belt-sanded down the opposite ends of the scrap pieces and applied the DevCon the same as I did the Titebond III. I'll try my test again tomorrow after the epoxy has set up (third pic).
Curing conditions: In my house, 78º - 80º F for 24+ hours.