[rooster59]

Why does older powder data often show a greater powder charge as a max load than newer data?

Better instrumentation? Increased knowledge of properties of steel? Legal issues?

This is data from IMR in 1990:
1990 IMR Data (http://www.zumodrive.com/share/gEBMzFkNj)

For example, in new data from Hodgdon, powder
charge is 3.2 grains less than old-

270 Win 130gr, X grains of IMR4831, 3003fps 50,300 CUP 24" bbl


Old data from IMR:

270 Win 130gr, X + 3.2 gr IMR4831, 3110fps 53,600 CUP 23" bbl (1" shorter)

So why the change?

Thanks in advance.

[NCsmitty]

Welcome to THR, rooster59.

Mostly liability issues, but some powders have been reformulated over the years, along with more accurate pressure measuring equipment.


NCsmitty

[Walkalong]

Better, more accurate measuring today. Also much data has changed from CUP to PSI.

[rcmodel]

The switch from Copper Crusher (CUP) measuring equipment to Piezoelectric Transducer methods (PSI) have more to do with it the anything.

The old copper crusher method would show max chamber pressure, but could not conform fast enough to very short lived pressure spikes.

The piezoelectric transducer can provide a highly accurate trace all the way from primer ignition to the bullet exiting the muzzle.

The labs found some things going on they just couldn't see with the old method.

rc