Thread: Testing a conventional approach to load development

Originally Posted by gimp

Thank you. Your velocity guess is pretty good.


Observationally, there are many many people (including myself historically) loading over book max on this forum based on the "safe" approach of "working up" and observing pressure signs. Some of these loads/speeds posted are clearly well in excess of SAAMI max pressures for the respective cartridge.

I would hypothesise that of the 2 methods:

1. ignore book data and work up til you get "pressure signs"

or

2. stick below book max and work to a target velocity based on book max


#1 will result in more people running higher pressures than #2

Greeting @gimp and all,
First I need to say that I have little faith in "pressure signs" in guessing pressure. I went well down the rabbit hole on this one at one stage but no longer. Most have been pretty well debunked so the answer to method 1 is no.
Charge, velocity and pressure are all quite linear within the normal pressure ranges so I mostly work up to velocity rather than charge weight. Data for most modern cartridges is pretty good with the odd exception and it is rare to find recorded velocities that vary much from the book data. For cartridges like the 6.5x55 and 6.5-06 data is all over the place and a bit more finesse is required. About 5 years ago I got serious about working up a decent load for my new Tikka 6.5x55. Possible velocity in a calibre increases at about 1/4 of case capacity so I spent some time measuring net case capacities and calculating a max velocity at normal pressure for the 129 grain SST by comparison with other cartridges including the .260.
So I used a calculated max velocity to work up to rather than the charge. Slightly different than your method 2. The .260 is loaded to a slightly lower pressure than some other modern cartridges so there is a little more headroom there than some other cartridges.
One thing I have discovered is that some heavy jacket cartridges like the LRAB push both velocity and pressure up from their thinner skinned brethren. In the 6.5-06 a change from the Hornady 129 grain Interlock to the Nosler 129 grain LRAB pushed velocity up by 100 fps, equivalent to adding around 2 grains of powder.
Regards Grandpamac.