I have a question about twist rates!

[LRRPF52]

Does that actually work? Not being sparky, just wondering if the experimental error of that is enough to tell 1:8 vs 1:8.2,since everyone always says there are manufacturing aspects and its super common for a twist rate to be slower than specified (which I have no idea why that would be true ...)

Yes, this is how I used to measure my twist rate with a rod and piece of tape on it with an indicator/witness mark.

You can see where it makes a full rotation, then mark that length on the rod. Once the rod is removed from the barrel, measure how far that point is that it took to make a full revolution, and there is your twist rate.