I haven’t personally tried Hodgdon High Gun for 12 gauge 2 1/2” shells, but I’ve heard a few folks mention it as a good alternative when you're in a pinch for powder. Since its burn rate is close to Alliant American Select, I think you're on the right track. I’ve had similar experiences when I was searching for
lever action rifle parts—sometimes you just need to experiment with what's available. I once swapped out a part in my lever action rifle and noticed a big difference in performance. It’s all about finding the right match for what you need, and I’d say give the High Gun a shot if it fits the load specs you’re after.