Just how fast is too fast?

[Dogleg]

Much of the velocity is gained long after the peak pressure has been reached and is dropping off. Area under the curve is what really counts. Slower burning powders hold the pressure curve longer. Good barrels contain and seal the rapidly dropping pressure longer and more efficiently.

With the many variables it is possible to have higher velocity with less peak pressure. Hense fast barrels.

 

[Falconflyer]

I have similar velocities out of my 22 inch 270 using 7828 and the pressure is fine. If the pressure was high then I wouldn't have tight primer pockets and long life from the brass.

I don't believe there is any correlation between velocity and pressure. A really slick barrel will produce faster velocities at the same pressure than a rough barrel will, so will the bore diameter play a factor as well as a few other things such as bullet seating depth. The brass is a better indicator of high pressure than the chronograph is and measuring case head expansion is the fastest way to figure it out but case life will eventually tell the tale.

 

[rral22]

I have similar velocities out of my 22 inch 270 using 7828 and the pressure is fine. If the pressure was high then I wouldn't have tight primer pockets and long life from the brass.

I don't believe there is any correlation between velocity and pressure. A really slick barrel will produce faster velocities at the same pressure than a rough barrel will, so will the bore diameter play a factor as well as a few other things such as bullet seating depth. The brass is a better indicator of high pressure than the chronograph is and measuring case head expansion is the fastest way to figure it out but case life will eventually tell the tale.

There is a DIRECT relationship between pressure and velocity. Velocity higher than the manuals suggest is possible, is a very dangerous sign, and can be achieved only with increased pressure. Case life may well be a good indicator long after the fact, so short case life and loose primer pockets are proof that you have been in dangerous territory all along. It is true that some guns are "slicker" than others, but the differences in velocity due to such variances should not be significant. Bullet seating depth influences velocity primarily because it influences pressure. Primer "reading" is almost useless as a pressure indicator.

Having said that, velocity difference of less than 100 fps from "book velocities" would not worry me.

 

[Falconflyer]

There is a DIRECT relationship between pressure and velocity. Velocity higher than the manuals suggest is possible, is a very dangerous sign, and can be achieved only with increased pressure. Case life may well be a good indicator long after the fact, so short case life and loose primer pockets are proof that you have been in dangerous territory all along. It is true that some guns are "slicker" than others, but the differences in velocity due to such variances should not be significant. Bullet seating depth influences velocity primarily because it influences pressure. Primer "reading" is almost useless as a pressure indicator.

Having said that, velocity difference of less than 100 fps from "book velocities" would not worry me.

You just made my point. Of course there is a relationship between velocity and pressure but they're not linear ( I should have clarified that), you can have high pressure long before getting to listed max velocity just as you can get to max listed velocity before you get to max pressure.

 

[Boomer]

Sixty grains of newly manufactured H4831 under a 130 gr lead core bullet is nearly an industry standard for the .270 Winchester. Use it with confidence in any modern rifle in good condition that's chambered for the .270 Winchester, with an expectation of good accuracy, and good terminal performance on game. If you don 't have a chronograph, you can zero 2" high at 100 yards and confirm 6" of drop at 300 yards with the 130 gr Hornady Interlock.

 

[BCBRAD]

The difference between a slow and a fast barrel could be .0003" in groove diameter [Or bore diameter.]
It could be internal finish as well. Dave.

Could it be that the bullet is swaged to bore/groove diameter in its own length, then carry on down the bore already sized?

A tight or loose bore (especially the first inch or so) will have an effect on start pressure as will the jump to the lands.

The plus or minus resistance (psi) of this will produce varying velocities (generally faster or slower) .

I have noticed that a barrel (my velocities) will get slower as the throat erodes, unless I up the powder charge over time to maintain the original velocity.