How many pennies fit in your chamber ?

[preventec47]

This is a good way to know for sure what is happening
inside your barrel.  then compare the stack of pennies
with a fired cartridge side by side.

Sometimes the first penny jams in the forcing cone
but is easy to bump back out.  Just be sure all obstructions
are removed after playing around.

[PHATINJUN]

What does this tell you Kurt

[mcwoodduck]

OK on european guns ther is a stamp on the bottom of the barrel.
65 = 2.5 inch
70 = 2.75"
76 = 3"
Chambers.
If you are worried about shells that were made for rolled crimp you will be able to tell if you shoot a folded crimp and it is not fully open but this should not be the problem.
If you need short shot shells.
Look up RST and give them a call.  Alex is the president and is great about getting shells out to you.  Lat year I ordered a bunch of 20ga shells, 12ga and some 2 7/8 10ga shells.

[jpshaw]

Are you saying that 1 penny will equal 1 milimeter?  Those 65, 70 etc. European stamps are milimeters aren't they?  I can't remember how may L's there are in milimeter (millimeter).

[mcwoodduck]

Yes the 65-76 is millimeters.
I think a penny is thicker than a mm.  I think about 1.25mm but I left the calipers at home to be sure.
A dime is closer. 
Other than the european guns the american guns have the chamber stamped on the barrels.
if you think you have a short chamber and the gun really kicks for what it is, get some 2.5" shells and see what recoil is like after that.
My little french side by side is a pleasure to shoot now with the 2.5 inch shells. and they will work in all of my other 20 ga guns as well.
Again RST is great to deal with.  If they do not get back to you quickly it's cause they are hunting. 

[jpshaw]

I believe the English had a 2" 12 guage.  Thats back when they were allowed to have a shotgun.

[mcwoodduck]

There is even a 1.5 inch shot shell.
The brits went small when they went to smokeless.  Shells are 2 3/4" in order to fit 3 drams of powder and the fiber wad in black powder.
with smokeless not as much room is needed for the powder.  Some of them they cut back on the payload to 3/4 oz to 1 oz.
But the 1.5" shells will work in some pump guns, mainly the Win Pumps and if it will hold 6 3" shells in a tube mag then it will hold 12 1.5" shells or 9 2" shells.  Just a thought.

[jpshaw]

There is even a 1.5 inch shot shell.  Some of them they cut back on the payload to 3/4 oz to 1 oz.

Actually Revelation (store brand for Western Auto) sold 1 oz 12 gauge loading.  I bought them whenever I could.  They were a lot friendlier in a 5 lb 8 oz Topper.  I wish I could find them know for my 5 lb 5 oz Pardner.  They were fine for squirrel and rabbits and I think they patterned better then a 1 oz 20 ga load.  (1 - 6 - 3) were the oz, shot and dram equivelent.

[mcwoodduck]

Depends on the powder but you can get softer 1 oz loads bu changing the powder from Red Dot to Green dot.
The loading you refered to (1-6-3)  One ounce, 6shot and 3 dram equiv or 1200 FPS out of a 28" barrel.
But 1200 FPS load can be 9,000 PSI or 8,300 PSI depanding on the powder and the wad.

OH by the way I was looking in Double gun journal this weekeknd and saw an add for choke and chamer Gauges. 
I have some of the brass choke gauges and have them as key rings.  The only down side to them is they are based on .729 bore for a 12 ga and any new gun with an over bore will show up as improved when it is actually full.