"It was a dark and stormy night...."

I am guessing that the wad and shot create a vacuum when exiting barrel. This would pull the base wad forward. Dave

Holeshot:
Think of it... wad and shot are being propelled by positive gas pressure. When they exit the muzzle, there is no pressure. then the atmosphere wants to "neutralize" the pressure condition inside the barrel by rushing inward... could there ever be a vacuum between a pressure condition and a "neutral" condition?

Just thinking out loud. Possibly wrongly.

Best, Kensal

I think Jent has it right. Gas gets behind the base wad by going past the primer, As the shot charge goes down the barrel, the pressure drops, but there is still enough pressure trapped behind the base wad to move it into the barrel

Jent's theory is as good as any and better than most!

Thanks Jent!

very interesting... hope we get to the bottom of this.... charlie

Notes to go along with Sherman Bell loads spreadsheet.

Gentlemen:
As part of this thread, some posters made a rather strong point made about the base wads of Federal 10 Ga. plastic hulls coming loose upon firing and lodging halfway down the barrel -- obviously creating an obstruction.

These are the exact hulls I use in my old W & C Scott, so I decided to go beyond anecdotal evidence and pose the question directly to Federal. They have responded thus:


"From time to time we hear about the base wads of shotshells being "sucked out" of a hull and traveling down the barrel to obstruct the bore. In the past years we have shot millions of test shotshells in all gauges here at Federal Cartridge. We have never been able to duplicate or confirm that the base wad of a shotshell has become out to be an obstruction. While we may agree that it "could" happen the likelihood is so small that we believe it is not very probable. The only way that we believe that the base wad can get pushed into a barrel is for the primer o somehow get beneath the paper base wad, which would be extremely unlikely. We would also expect that in this unlikely event there would be an off sound and an incomplete ignition of the shotshell. We hope this information has been helpful.

Thanks
Federal"

This may, or may not, convince certain posters on this site. But it tends to put my mind at ease.

Best, Kensal