Hi, Bob:
Thanks for your comments.
The Lyman "manual" was edited by Ken and I gave mine away. Sorry.
It was a large format, 3/4" thick, 12" X 14" or so, not the usual Lyman manual size.
Have looked all over for one, but it is the one with Minie ballistics in the back.
Both chrono results and some "spark" photo's were included.
One showed the expanded skirt a couple inches beyond the muzzle.
There are lots of UTUBE slo-mo vid's showing the muzzle of center-fire rifles with a puff of smoke preceeding the bullet's exit. Same for shotshells.
Peters Ctg Co published a small booklet in the 1930's full of spark photo's showing shot charges leaving to muzzle. All had gasses in front of the charge.
Dr. Oehler said it was a "pressure wave", not particulates from unburned powder that could trigger the start "Skyscreen". I think OUR relatively slow bullets are involved.
Again, it is from muzzle closeness. I used a 1\8" thick plywood 12" square sheet with 4" round hole located a foot in front of the first screen. Careful, careful. No one shot through it but me. Have seen several nice screens of others perforated by range rats not aligning correctly.
Trying to chrono m-l shotgun loads was a challenge because of not only that pressure wave, but also the erratic sensing of pellets by the screens. Had to use an induction coil to sense the main body of the charge vs. leading pellets or stray ones.
Might Google spark photographs of bullets.
Dr. Oehler and I spoke about five years ago. He may still be around. Very nice fellow.
Regardless, the shield solves the problem.
Bullet overstabilization, tipping at muzzle exit and the "Magnus" effect should get your brain going. Haha. Love.
Kevin
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