Today, many ammunition companies have attempted to standardize the color of 20 gauge shells to yellow but this is not true 100% of the time. A problem can result because the 20 gauge shotshell passes through the chamber of a 12 gauge shotgun and will lodge in the bore just forward of the forcing cone area. This done, the following 12 gauge shell will still fully chamber but the 20 gauge shell has created an obstruction in the barrel which will almost surely cause a catastrophic failure to occur upon firing.
The answer to this potential problem, like so many safety issues is very simple. Develop a good safety regimen. Always, always, always, check the ammunition before it is inserted into the chamber of the firearm. As with checking for a bore obstruction each time you load, this safety habit can save your firearm, and prevent a possible injury. Pre hunt planning and checking to see that only the proper ammunition is on hand is a great habit to develop too but nothing is as good as checking each shell as you load.
---- News Release, Jan. 2000
H&R 1871, Inc.
60 Industrial Rowe
Gardner, MA 01440
Other Resources:
Firearm Information: Shotshells and Loads
Idaho Hunter Education Program
Single-Shot Guns aren't Sporting (for Sporting Clays)
by Al Hubbard
BOOKS FROM AMAZON.COM
Shotguns for Wingshooting
by John Barsness
Fool Hen Blues: Retrievers & Shotguns and the American West
by E. Donnall Thomas, Christopher Smith (Illustrator)