Here is more from The High Road
https://www.thehighroad.org/index.php?threads/winchester-97-chamber-size.390434/snip-------------------------------------------
Some clarification is in order.
The barrels from Winchester of classic era had plenty of barrels on 97's that had no chamber length markings, but measure the same as those barrels WITH 2-3/4" markings.
For instance: every Model 37 12 ga. is a 2-3/4" marked barrel, but measures as a nominal 2-5/8" or 2.6"
A pair of Model 12 16 ga. barrels marked 2-3/4" that measure at about 2.6"
A pair of '97 barrels with patent marks of 1900 and 1901 measure the same as an "E" model, about 2.6"
The only typical problem vs. paper/ plastic hulls is in the port configuration on M-12's, for instance, not wanting to clear a more stubborn star crimp end of a plastic hull.
Was there going to be necessity to mark a barrel already proofed for the most modern length shell available at the time (2-3/4")? The 3" magnums didn't come out till much later, and that is when all new barrels would have been prudent to mark.
Realize that every one of those barrels would have been proofed by Winchester and claimed by them to be safe at the time of manufacture. If they are marked 2-3/4, they should be considered safe. If they measure the same as one marked 2-3/4, they should be considered safe, regardless of lack of marking.
See that proof mark on the barrel? Every factory marked Winchester barrel will have one. That barrel and the gun are safe. A mechanical check of the safety and locking parts of the mechanism are more important than chamber length precision.
Those chamber lengths, regardless of whether marked or unmarked, being within 1/8" of a full 2-3/4", have no significant pressure change compared to any other chamber that is at 2-3/4", and are not in any way a danger to the frame or shooter. Period.
I don't discourage lengthening forcing cones for better patterns, if done the way that I do them, but chamber lengthening is not something I would push by fear-mongering.
Any tale of a short chamber causing extreme pressure is something I had once believed myself, but no longer.
Any '97 frame cracking is NOT caused by a measly 1/8" of chamber. NO way, no how.
I don't see how anybody could make that claim (honestly) if they had no idea of the history of the gun- once owned by an amateur reloader, for instance.
Reloading with wrong powder/charge MAY do something to the safety factor, but even the more fear-mongered example of shooting 3" shells in a 2-3/4" chambered barrel does not make the 3" shell have any significant boost of pressure with a bit of the crimp laying in the forcing cone.
The 2-3/4 barrel may not have been proofed for 3" load pressure which is slightly higher than 2-3/4 proof, so don't say that I am saying 2-3/4 barrels are OK for 3" shells. I am saying the individual shell does not get a lot higher pressure from a different chamber length.
EVERY manufacturer and SAAMI will tell you that you are to shoot how the barrel is marked and no longer than that.
You should not expect them to tell you that shooting a longer shell is not a huge safety issue. Problems may arise when shooting a long 3" shell in an old loose and wobbly single shot, but that was foolhardy to use even with target loads.
Did you ever wonder how a gun got to be so loose? It must have been shot well past the slight wiggle stage, and still didn't take off somebody's face. The barrel is still intact and not ruptured.
Do you think that guns are really that easy to damage, with a tiny shell/chamber length difference?
Guns, like many mechanical contrivances, are over-built for a safety factor. Recognize that link chains, for instance, have a working load about 20-25% of breaking load.
You will also notice that I do not take into account any good or bad influence of a pattern with the shell being slightly longer than the chamber since this discourse is about safety.
Winchester had a '97 taken off the assembly line and put into ammo testing service for well over 20 years and a definite million plus shells. They wanted to test pattern performance on a well-shot barrel, and that one still rated in a passing level for the full choke that it was marked, so, so much for shooting out a choke with lead shot. I'm sure that gun and barrel saw many high brass hunting and buckshot loads.
I have spent much time conversing with personnel at Remington, from the last ammo plant manager, to corporate higher-ups, to the gun plant service manager. That guy has been Remington his whole career, and some of that time was in the testing area.
That is where they don't see if a gun is hurt by a load, they find the load that blows the gun apart. Repeatedly. Talking to him is the next best thing to seeing the exploded residue for myself.
When he says that pressure readings don't spike due to short chamber/long shell interference, that is a fact.
There are enough circumstances that can make shooting a gun potentially hazardous without keeping another old wive's tale alive.
Don't take a measurement of a chamber gauge being off 1/8" to get into a panic. I would not expect to use that as a money maker by playing on someone's fears. I do not mind a proper and exact chamber length, but shotguns are a lot different than rifles and throating conditions.
Perfection is a great thing to have, and I will make things precise for somebody wanting that. I'm not going to exaggerate to get somebody worried enough to have something changed.
If anybody pushes you to change one of these barrel examples for a safety reason by claiming a slightly short chamber is a grenade waiting to happen, ask them where their research lab is located or what other evidence they have.
Damascus barrels blowing up from smokeless powder is another one of those old tales, at least from the time when both barrel types were in production.
The loaders of the day could get bulk or dense smokeless powder.
Bulk powder used the same powder dipper as the black powder, but the dense powder used a tiny powder dipper. What happens when they get mixed up? Triple charge?
That must be the fault of the barrel, right?
If you ever saw the test of a load of various damascus and fluid steel barrels being loaded to destruction, you would not think damascus was weak, any more.
Some examples had so much powder and shot (well over 4 ounces for some, I believe) that the barrel was filled about half way. Some of the examples had actually welded the shot into a plug that failed to exit, and all the powder gas vented out of the fuse touch-hole. No ruptured barrel, in some instances, even at that extreme. Some of the best rated were damascus.
I need to dig out the Double Gun Journal with that article inside.
kirbythegunsmith@hotmail.com
endsnip---------------------------------------------------
BUT here is an opposing view from shotgun world
https://www.shotgunworld.com/bbs/viewtopic.php?f=2&t=471434from Dustman47
snip--------------------------------------
A little straight talk on shot shells, shotgun chambers and forcing cones is needed to clear up some of the confusion and misinformation frequently posted on shotgun forums.
When talking about these things it is important to account for the era in which a shotgun was made as unfired and fired shell lengths and chamber length have varied through the years but have become more standardized in the last half century.
The fundamental anatomy of a shotgun barrel begins with the straight walled, cylindrical portion known as the chamber, in which a shot shell resides during firing. That is the portion denoted on the barrel and boxes of shot shells, as the chamber length and will be, 2 ¾”, 3” etc. Older shotguns may not have such notation. The chamber length is NOT the length of unfired shot shell but the length of a fired case that opens up into the straight wall chamber. When fired the casing opens up to release the shot and in doing so becomes longer, as opened, than it was closed. All shot shells are closed on the end by a crimp. Most all modern shells are closed with some type of star crimp but shells from older eras had simple rolled crimps with cardboard disc holding the shot in place. Rolled crimp shells open up shorter than star crimp shells of the same unfired length. The length of unfired case will vary a little among manufacturers by the type of crimping they use but thanks to the standardizing of “Sporting Arms and Ammunition Manufacturers Institute” (SAAMI) they will open up to their stated chamber length. Do not, on any gauge, be mislead because you can drop a 3” shot shell into the chamber of a 2 ¾” gun. An unfired 12 ga., 3” shell is only about 2 ¾” in length and will drop into the chamber of a 2 ¾” gun because the chamber is sized for an opened up shell case not a closed one. But, when fired a 3” shell opens up about another ¼”. Then there is no straight wall chamber length left in a 2 ¾” chamber to accept it and it has to open up into the smaller diameter of the forcing cone area of the barrel. That condition amounts to a constriction and leads to high barrel pressures that can be damaging to the gun and shooter.
Many older guns will have short chambers and were designed for a variety of chamber lengths as there were not always industry standards that now exist for modern shot shell and firearms manufacturers. Older guns can be re-chambered and their forcing cones lengthened to handle modern shells. Many shooters get away with it in older guns but shooting modern shells in an old gun chamber that was not designed for them is a bad practice. Many modern guns are designed to handle more than one shell length with some compromise in performance to handle different lengths.
Immediately following the straight wall cylindrical chamber there will be a conical section known as the forcing cone and there is no set length or angle of this section and it has varied significantly over time as shot shells have improved. The forcing cone will begin at the diameter or the chamber and reduce, over some short distance, to the bore diameter of the gauge shotgun it is. From there the barrel will be bore diameter to the muzzle where various size constrictions are applied known as choke. The intent of the forcing cone, before the near universal use of shot cups in shot shells was to force the mass of shot into a compact column coming down the barrel and minimize pressure gas leakage through and around the shot column. With modern shot cups the shot stays together inside the cup and the cup resists gas leakage until exiting the barrel. With shot cups the forcing cone doesn’t play its original role. However, one can still buy shot shells that don’t have shot cups and the forcing cone is still important for those shells.
endsnip----------------------------------
Now, with all that said, if it were me I would only shoot "shorter" shells with rolled crimps.
I personally see no problem with using a shell that fits the chamber, and rolled crimps keep that extra plastic from increasing pressures: