Back in the 80's I use to load H-450 in my 270 Wea mag. My max load with a 130 gr Hornady was 74 grs of powder. Came time that I had to run a new lot, so I backed off to 71 grs and worked up. When I got to 74 grs , my old max, vel and pressure was way low and accuracy was bad. I decided to continue working up. Only when I got to 78 grs did vel, pressure and accuracy return to the old levels. There was no danger because lucky for me I went from a fast lot to a much slower one, but I've often wondered what might have happened if it had been the other way around. Since then , depending on case size, I always back of at least 4 or 5 grs and work back up. It does not cost much to be safe, just a few primers, bullets and little powder. JME