Originally Posted By: JHZR2
No concerns. Just want to be gentle on it, thought it was the "right" thing to do.
Too low of pressure and the impulse behind being "worse" makes a lot of sense.
It's a "bit" like detonation in an IC engine.
With a case full of powder, the primer starts the fire at one end, and through a combination of chemistry and powder flake shape (that last one itself is fascinating), the rate of burn is controlled.
With light charges of powder, ignition is not so precise...if the powder has settled along the bottom of the case, or due to last activity with the firearm settled at the primer end or projectile end, the primer flash can be exposed to a large initial surface area...initial combustion point and volume can be very different. (Back in the Shooter's Online Forum days, one of the more experienced guys was showing that he could get hundreds of fps difference by pointing the muzzle up or down before firing a light load.
It's why a lot of pistol powders are manufactured so bulky
Here's the Lee powder scoop charts
https://leeprecision.com/cgi-data/instruct/Dippers.pdf
See the difference between rifle powder (say AR2208, sold as Varget and Red Dot).
It's also why light loads have often included a kapoc of pillow stuffing wad to hold the powder near the primer.
Double base powders appear the most sensitive, as they are plastics made incorporating nitroglycerine in the nitrocellulose matrix (single base are nitrocellulose, controlled by degree of nitration, fillers, and grain shape)...there's evidence that the nitroglycerin can volatise out under some conditions, and go "bang"