We tested loads at both maximum normal pressures and at the starting loads (some labs calculate start loads — we shot them). Standard primers caused no ignition issues at the max load but posted higher extreme variations in pressure and velocity in the lower pressure regimes of the start loads. In extreme cases, the start loads produced short delayed firings — probably in the range of 20 to 40 milliseconds but detectible to an experienced ballistician. Switching that propellant to a Magnum primer smoothed out the performance across the useful range of charge weights and completely eliminated the delays.
If I've recommended a Magnum primer in reloading data I've developed, it's because my lab results show it's needed.
I'm getting similar velocities with a case full of H1000. I used LR primers without issues.Latest range results using IMR7828...
95gr B-Tip 53.0grs IMR7828 Ave(3) 3282 fps Es 65 Stdev 35 65 Degrees
100gr Partition 54.0grs IMR7828 Ave(3) 3145 fps Es49 STdev 25
86gr F-Tip 54.0grs IMR7828 Ave(3) 3286 Es52 Stdev 26
All the loads are running 100-150 fps under Quickload predictions even after I updated the actual case capacities. I've been using CCI 200 primers. Seeing the large deviations I am suspecting that moving to a Magnum primer might improve velocities and lower variations. I am also noticing some smoke left over in the barrel and chamber. Although it doesn't seem like you would need a Magnum primer to light-off powder charges less than 60 grains.
Thanks.No data for 240 wby. https://imrpowder.com/imr-enduron-7977/
Contact Hodgdon. https://imrpowder.com/company/contact-us/
IMR 7828 has data at Nosler & Hodgdon. "C" = Compressed Loads.
The burn rate chart lists 7977 as slower then 7828. May not be able to get enought 7977 into the case for top velocity.
I would look for IMR 7828 SSC .
That's what I was hoping for. I don't have quick load and the powder suppliers don't care about it because it's an uncommon cartridge.The 7977 is a double based powder containing nitroglycerin. The nitroglycerin should produce more energy per grain. May require less powder & fit in the case, providing maximum velocity?
The 7828 is single base powder. So it may benefit from a magnum powder?
https://imrpowder.com/resources/safety-data-sheets/
I posted Hogdon's reply. It was basically you shoot an uncommon cartridge so tuff luck.Contact Hodgdon. They might can help.
You could start with starting load for H4831, and work up one grain at a time watching velocities and measuring case head expansion.
Old school way...