Using shot shells in chambers that are not the correct length for the shell
This question comes up innumerable times. Shotgun chamber length has changed many times over the last 100 years or so. There is for the 12 gauge 2”, 2&1/2”, 2&9/16, 3”, and 3&1/2” and I probably missed one.
In any event for various reasons individuals do not want to use the correct shell length. It may be due to availability, price or just plain lazy. These individuals search for a universal prescription that will allow them to use longer shells than the firearm was designed for. Some conduct ‘back of the barn tests’, publish the results in non-scientific journals and crow about themselves. These results are then accepted as a universal prescription, that this is indeed safe.
Some want to use standard factory loads, some low pressure loads whether factory or hand loads.
With myriad of firearms out there with different chambers, different steels, different heat treats, not to mention that many are of considerable age and have had ‘hard’ lifetimes not to mention who knows what type of refinish including heat treatment.
Couple that with the vast array of shot shells which includes the hull material, wads, powder and manufacturing techniques, it all leads to so many variations that no one can develop a universal prescription for all usage of longer shells in short chambers.
So, in effect, what you are doing when you use a shot shell not designed for your shotgun is a form of Proof Test each and every time you fire the shotgun.
SAAMI
http://www.saami.org/ was tasked in 1926 by the Federal Government
• Creating and publishing industry standards for safety, interchangeability, reliability and quality
• Coordinating technical data
• Promoting safe and responsible firearms use
As such, this is what they say,
"UNSAFE ARMS AND AMMUNITION COMBINATIONS
The discharge of ammunition in a firearm that is not designed to shoot that ammunition can be dangerous and can result in serious injury or death to the user and/or bystanders, as well as damage to the firearm. This unsafe condition is caused by an excessive build-up and/or release of high-pressure gas in a firearm's chamber, barrel and/or action beyond which the firearm is designed to withstand. Therefore, in the interest of safety, you should use only ammunition of the caliber or gauge designated by the firearm manufacturer for use in that firearm. Markings indicating the correct caliber or gauge of ammunition to be used in a firearm are usually found on the firearm's barrel, frame or receiver.
One way to verify that you are using the correct ammunition is to check the head stamp on the ammunition to confirm that it matches the caliber or gauge markings placed on the firearm by the firearm's manufacturer. Some types of ammunition do not have markings on the head stamp of the cartridge. In that case, check the original ammunition packaging to determine its caliber. If you have any doubt about the caliber of the ammunition, you should not use the ammunition until you have it examined by a qualified person who can determine its caliber. Remember just because a round of ammunition can fit into a firearm's chamber, barrel or action does not mean it is safe to use that ammunition in the firearm.
Due to the availability of many different shapes and sizes of ammunition and firearms, there are countless unsafe ammunition-firearm combinations such that a comprehensive list of unsafe combinations is neither feasible, nor practicable. Below is a list of some unsafe combinations that are well known because of somewhat similar chamber and ammunition dimensions.
If the caliber or gauge is not clearly marked on the firearm, or if it appears the original markings on the firearm have been altered or modified in any way, do not use the firearm as serious injury or death could result to the user and/or bystanders, as well as damage to the firearm.
Similarly, SAAMI has not published voluntary recommended practices or procedures for re-chambering of firearms. It is possible the re-chambering of a firearm may not have been done properly or may not have been properly marked on the firearm. If the caliber or gauge marking is missing or altered in any way, you should not use the firearm. You should instead have the firearm examined by a qualified person to determine what caliber or gauge ammunition can safely be used in that firearm.
If you read the above closely, you can see that SAAMI also cannot give a universal prescription,
“Due to the availability of many different shapes and sizes of ammunition and firearms, there are countless unsafe ammunition-firearm combinations such that a comprehensive list of unsafe combinations is neither feasible, nor practicable.”
I have read all the above Posts, some are from knowledgeable individuals, some are plain drivel from Posters who know they Post drivel and some are from well intentioned individuals but not technically based.
None can supply a universal prescription to make your mind at ease when firing shot shells not designed for the shotgun in question.
The risk is yours.
Accept the risk and do what you want.
There is no easy way.-Dick
EOT