I have a number of reloading manuals on the shelve dating back to the 1960’s. And I just purchased Hornaday #7, and Serria #5 to update my knowledge base. You are correct most manuals do not match up.
Most Sierra data I have used calls for less powder then the old Hornaday and Sierra manuals. In my opinion Sierra data is right on for Sierra bullets in my rifle. For a long time I was loading other brand 150 grain bullets in the .270 Winchester. I had to drop my charge a full grain and a half when loading the Sierra 150 grain .277 boattail. I think the bearing surface on the Sierra bullet is greater.
Most manuals recommend starting low when starting a new load and working up because of the differences in components. Recently I ran out of a long time pet powder and when it came to restock I purchase 2-cans with the same lot number. I do not want to start from the bottom every time I empty a can of powder.
Sometimes manufactures change a component but keep a favored brand name. Years back I purchase a supply of .277 caliber, 140-grain Winchester Silvertip bullets. The original Silvertip had metal Silvertip, today’s Silvertip is made of plastic and the bullet is of a different design.
Marketing is a selling ploy that does not always take safety into consideration. When I started loading surplus 4831 it was the only 4831 on the market. When the surplus supply ran out Hodgdon had it manufacture in Scotland and called it H4831. The IMR came out with a slightly faster powder called IMR4831. The IMR4831 is a good powder but it created a safety issue because it is faster burning then 4831/H4831.
If you scroll down the post link I describe the process I use now days to develop loads. I have used this process for a lot of years loading a number of calibers. It is time consuming, but I believe it has paid off. The last few years I have inserted the Chrony in the process. One of the lessons learn is that while manufactures may publish a certain velocity, the same factory number may not come close to published data because I am shooting a different firearm, at high elevation, and most likely my barrel is shorter then the test barrel.
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