Yes,
Happens all the time. All of those variables that you know about are causing the difference.
Fast barrels and slow barrels.
Some primers can give a difference of 100fps
Some brass cases have way more, or less capacity and several grains variation for max loads can be normal.
Powder lots.
Primer lots
Chamber throat differences that vary rifle to rifle, and change drastically with round count in the same rifle.
Chronograph differences.
Sometimes i get wayyyyy better velocity than the book says, then hit pressure early.
Sometimes i get wayyyyy lower velocity than the book says.
I almost always load up until i see pressure signs, or groups that are clearly deteriorating at the high end. Then you know where the top is. Of course you confirm that the cases will hold a primer again, and then again.
Also,
If you are using some kind of coated "slippery" bullet, you will need more powder to get the same velocity as a "dry" bullet. The equation works in such a way that you can load more powder, and get more velocity than a dry bullet.
I have almost all of the reloading manuals. The differences between book to book for charge weight/velocity on the same weight bullets is drastic to say the least. But i suppose most use different brand components. I don't take those books as gospel. Just a guide line.
Some companies do seem to have some fast test barrels.... I agree on that also.
