Have not seen him. I do shoot a lot of duplex loads

by JohnKDM, Tuesday, March 12, 2024, 12:38 (47 days ago) @ Slow Hand

using SR4759 under Swiss 1.5 & 2f. Primarily for double rifle regulation as our BP is not equivalent to the original Curtis & Harvey #6. It does burn a lot cleaner with the smokeless kicker and since 1gr of smokeless is roughly equivalent to 3grs of BP, when you run out of case volume you can offset by adding the smokeless up to a certain point. S. Bell and G. Wright discovered when pressure testing you can overdo the kicker and exceed the original pressures. Most pressure tested safe loads keep the smokeless less than 10% of the BP charge. Aside - fillers, usually the dense ones, can raise pressures.

When he put the smokeless on top and gained velocity you notice he had flattened primers. Of course primer visuals are not always a good indicator, but what I think happened there was the smokeless lit after the BP pressure peak and caused a secondary wave peak. There was a French scientist (Paul Vieille) that worked with the effects of a pressure wave bouncing back and forth in a closed cylinder - and if it got in sync with another wave, the peaks combined and increased pressure as they bounced back in forth in a closed cylinder and slammed into the ends. His work using these ideas led to nitroglycerine being developed into smokeless powder (controlled burn instead of an explosion). This concept is a good theory behind barrel ringing at the base of a bullet if an air gap is left in a BP case.

Even though the bullet is moving, it might apply here as well.