The real real question is: How does ANYBODY have any idea? You and I both know that every rifle barrel is different... they tell you as much in your "reloading manuals". So, how close are they? 2%.... 4%.... 15%? I'll trust my eyes, ears, and the empirical evidence before I trust the data shot in ONE BARREL as gospel. You gotta use your coconut.... even within 'book data', cause you ain't shooting their barrel.
Precisely...and these differences can never be underestimated.And also why we really don't know when we use data from the manuals that we are blissfully operating at or in excess of SAAMI specs, and conversely we could still be within those specs even if we do exceed manual data.
This is precisely why a chronograph is so essential,and while not perfect as a means of measuring pressures, it should at least serve to tell us when we are over the top.
it isn't always enough to say...Well I stuck to manual loads and got 3300 fps and the SAAMAI data says I am at 65,000 psi so everything is OK...
No not always.I recall one 7 mag with a Krieger barrel that gave 3080 or so with a 160 and manual load;and a second 7 mag with a Douglas tube that gave over 200 fps more velocity with the same ammo.
But the velocity of well in excess of 3200 fps was too much velocity for that case, which I knew,and backed down accordingly with that rifle.
And before someone starts thinking the 7 Rem Mag is the only cartridge afflicted this way, forget it because I have seen precisely the same thing in 270's, 280's, 300Win and Weatherby,and a host of others.And I have also seen factory ammo for the 7mm WSM give velocities that a 7mm Mashburn tops out to meet,and had ejector slots ironed into the brass....I am sure the stuff was supposed to be within SAAMI spec,but not in that barrel that day.Per Federal,It was loaded to 65,000psi too.But I did not let that serve as tacit license to chase those velocities and frankly could not come close with my hand loads.
So when you see your rifle give extraordinary velocities with stock manual loads it isn't always carte blanche to assume everything is OK and you just have a fast barrel...it may be a warning to back down.
Like dogshooter says you gotta use your noodle with this stuff.
Another thing besides the obvious issues associated with custom tubes, trued actions and straight taper cases which all conspire to hide traditional pressure signs, is what Bob Hagel noticed adn wrote of years ago, but which rarely gets mentioned anymore, and that is the smaller area of the case head on an 06-based case will tend to show pressures signs less quickly than the larger case head area of the belted magnums.
Add all these little things up and it is not hard to understand why some are running velocities off the chart but think everything is completely OK because they are religiously sticking to tested manual data;well maybe so but there is just as good a chance that the extra velocity you are getting is not free,and is an indication that you are already off the charts or close to it.
Seeing all this stuff over many years is why I eventually got to the larger 7mm cases like the Dakota and Mashburn....not always for the extra velocity they are capable of, but also because when I see 3200-3300 fps from a 140 gr bullet I know I have lots of slack and safety margin in my loads.
