Chamber Issue

[Machine Tom]

So I fired the Strong Cannon the other day and found the cartridge difficult to extract. After looking over the cartridge the crimped end was really stretched, and this was the issue of the difficulty in extracting the shell. So I stick the bore gage and measure the chamber, at the 2.5" spot the chamber just opens to about a inch in a distance of .2-.3". The Winchester shell plastic is very thin, much thinner than the 30 year old shells for my 12 ga.(I should measure)
 
So were the old shotgun shells brass with plugged ends, or paper. The crimped lenght of the plastic 10ga blank is 2.560+/- .
Thinking that a brass shell did not need the support of a chamber when used in a non-projectile application. That is why it was made this way.
 
There looks to me only two solutions, live with it or rechamber the the barrel.
 
(edit) Was there ever a 2 5/8" 10ga shell, the blanks are all 2 7/8"

[onegreatshot]

Tom before going to all that trouble  search the internet for brass made 10 hulls. There is a company that makes them. Maybe he can custom make your chamber size.  I found him when I was attempting to buy a Winchester 10 cannon. Deleted the site when I found brass cannons.

[onegreatshot]

Try Midway reloading for an accessory that is used to cut the hull to length or go to buffalo arms co. That might know where a 10 ga. hull can b found.

[GGaskill]

You might consider cutting your shells off at 2.5" and closing the mouth with a card wad sealed with water glass (sodium silicate) instead of a folded crimp.  Brass shells are loaded the same way.

[flagman1776]

I know a lot of old shotguns have rare chamber lengths...  but I'm no expert, so I looked it up.  10 gauge is/was offered in 2 5/8", 2 7/8", 3, 3 1/3".  Cartridges of the World; by Frank C Barnes, 5th edition, page 320 
So, YES, there were 2 5/8" shells.
Guns made for roll crimp or just an over shot wad, would have different barrel chamber dimensions than those made for modern shot shells where the crimped end would need room to open...  and be prevented from over expanding to allow extraction.  It does seem odd that the bore is cut wider in this way beyond the chamber, but these were built to be blank guns.