Originally Posted by
Kevin Tinny
...using a chrono for black powder involves some tricks. I have used three models of OEHLER's and Dr. Ken shared some important B-P tips that current chrono mfgr's don't include in their directions. A blast shield is necessary to prevent the bow wave BLAST OF THE POWDER (which can run AHEAD of the projectile for up to 30 feet) from triggering the start screen. Yep, for sure! This can MASK issues and STILL register nice, uniform velocity spreads. There are special photo's showing this pressure bow wave AHEAD of MINIE's in one Lyman Handbook edited by Ken Ramage in the 1970's.
I wish we had a utility on this board to start a new thread based on information in a prior one. This comment intrigues me no end. Because I've come to believe EVERYTHING Kevin posts is accurate, I wanted to learn more about this effect.
First, lets separate what exits the barrel behind the bullet. I had to make lexan blast shields because the plastic cover on the front sensor of my chrony was destroyed when I was testing cartridge gun loads. That was caused by the chrony being too close to the muzzle and the unburned powder and hard residue that is contained in the muzzle blast of a bp explosion.
The pragmatist in me says that no way can something leaving a barrel behind a bullet overtake that bullet, if everything is propelled by the same force. (It's like the old time Sharps shooter who insisted that pushing a bullet and loose powder charge into the chamber could allow powder to get in front of the bullet and into the barrel.)
I do know that the blast can affect a bullet as it exits because at that point the bullet is no longer supported by the crown. That effect is supposed to be limited to a tipping caused by uneven pressure at different points of the base. Out in the atmosphere, where everything is equally affected by gravity, barometric pressure, humidity and wind, I can't see that wave ever catching up to even the base of the bullet let alone passing it.
I tried searching for information from Ken Ramage, but it looks like he gets credit for editing the Lyman handbooks for many years. There were no specific articles or even pictures I could find about bow waves and chronographs.
Kevin, do you have any specific articles or photos to support your statement?
"Help me, Obi Wan. You're my only hope."
Last edited by bobanderson; 12-07-2018 at 09:18 AM.
Reason: grammar
Bob Anderson
Company C, 1st Michigan Volunteer Infantry
Small Arms Committee
"I won't be wronged. I won't be insulted. I won't be laid a hand on.
I don't do these things to other people, and I require the same from them."
- John Wayne in "The Shootist", 1976
Bookmarks