Originally Posted by Steve Redgwell
Originally Posted by alpinecrick

This year, one of my 270's was packing a 160g NPt with 59.2g of IMR7977 with WW cases and WLR primer--the same as Hodgdon was using in their pressure data--for an average velocity at 2804 fps with a 22" bbl.

Hodgdon's max charge was 60g and using a 24" bbl. I'm assuming Hodgdon's is using piezo pressure gun, and the chamber would be at SAAMI minimum specs which tends to produce more velocity than our joe average bbls, factory or custom.

My rule of thumb is to subtract 20fps per inch of bbl when comparing my loads to pressure data. In other words my 58.2g of powder is probably right there at max pressure. 60g would be most likely be over pressure and as it's been noted by JB and other articles I've read pressure signs don't generally show up until well over pressure.


Your response outlines one of the dangers of using a chronograph when doing load work ups, and why reloaders can get into trouble.

Imagine for a moment that a new reloader reads in his manual that a certain bullet and load will generate 2800 fps. Does he confirm how the manual determined the velocities? Does he know the barrel length of the barrel used in the manual? using what equipment? Does the manual even publish this information?

Let's say the manual states that they used a 24 inch barrel and got 2800 fps. Our reloader has a rifle with a 22 inch barrel. He loads the max and only gets 2720 fps - according to his chrono.Assuming his chrono is accurate, he decides that he can increase the amount of powder until he attains 2800 fps. Can he?


If he sacrifices the correct color of chicken, yes.

But seriously, of course he can. He can schit in his own shoes if he wants to. Is it safe to load over-pressure? Likely. But the question becomes, "When does it become unsafe?" A few thousand PSI, say to 68K PSI MAP on a very consistent load velocity-wise, likely isn't going to be noticed, let alone likely unsafe.

I belong on eroding granite, among the pines.