Re: IMR4895 vs H4895?
I have used several JUGS of IMR 4895. It's a good powder.
If you look at the burn rate charts they are listed as the same, or very close. It all depends on who's burn rate chart you look at. Some people say you can use them interchangably. But I would drop a grain or two and work back up to be sure. At the very least, I would test it as a different lot number.
When you finish the tests let us know what you found.
EDITED TO ADD: For a long time Hogdgon powder wasn't available in this area. That's why some of my data is dated in that manner. Also why I tend to favor IMR slightly. Most of that was available just driving into Knoxville, (25 miles).
Good luck.