quote:

Originally posted by 375HH:
Hi
I am in the process of completing a .450 Nitro Express 3,25”, Falling block rifle, Fields Pat, no. 1927.
The rifle was not completed back in the days. The action is for example not hardened. No stamps, and so on.
Before I put too much money and time In this project, I have to develop a proof cartridge that, will produce 30% over pressure.
I started with the max load of 82gr Vihtavouri N150. Hornady 500gr RN Interlock.
GRT give me 648m/s. My Chronograph says 614m/s. approx. 6% difference.
Everything looked good. Nice round primer and no extraction problem.
Then the weather got worse, and it was time for my, according to GRT +30% load, 90gr N150. The chronograph did not register it.
Nice round primer and no extraction problem even now.
How shall I calibrate GRT?
Can I expect he preasure values in GRT to change, and follow new loads?

/Johan