Thanks for the info. With my .257 WBY, a Mark V with 26" barrel, I got 3251 fps ave. with 120g NPT and 75g of LRT and a Fed 215 primer. I notice the Hodgden site says 76.8g and 3218 from t a 26" barrel. So, mine at least showed better, but Chronos and barrels are different.
Well, yeah.
My results were chronographed with a Magnetospeed, which like all my several chronographs was checked against an Oehler 35P. It recorded very similar velocities--given the difference between the MS being right in front of the muzzle and the 35P being set up with the first screen 15 feet from the muzzle.
I have also encountered very different velocities with different lots of NEW powders many times over the years. A good example would be IMR4451. Got a small test sample (2 pounds if I recall correctly) from Hodgdon when it appeared, and was impressed enough to buy an 8-pounder when they became available. There was close to 100 fps difference in the two powders when using the same loads in the same rifles.
This isn't uncommon with NEW powders, because different lots often vary considerably. This is "smoothed out" over time by mixing various manufacturing lots to come up with a more consistent product. Which is why I eventually blended my first two pounds of 4451 with the 8-pounder--and the resulting velocities were very similar to what are now reported on Hodgdon's site.
This may be the "problem" with my batch of LRT. I was sent a couple pounds as soon as it appeared, which may be different in burn-rate than later "blended" batches.