Miller, Jim and Larry, Chuck, and others,
All of you bring up great points and a lot of your knowledge about this subject. For me it is a little too deep. I reload low pressure, low velocity shells in 2 1/2" and 2 3/4" for some old L.C. Smiths I have. Mostly because I have the time to do it and because of the loads I want. None were ever tested by me, but all the loads were from either tests done by Tom Armburst for the 16 ga Reloaders Group or form reloading guides.
I don't shoot 2 3/4" shells in 2 1/2" chambered guns, why, because I don't feel it is safe. I'm positively sure that previous owners of the 20 ga "elsies" and 16 ga "elsies" I have had 2 3/4" shells through them, why, because ignorance is bliss. Most people that buy older guns have no idea what the chamber length is and just shoot todays modern loads designed for heavier payloads. This is why a lot of the L.C. Smiths we see have cracks behind the sideplates. This was especially true from the 50's-80's when we didn't have the selection of shells we have now. Shells then were loaded Magnum or Maz loads and people just used them, and I'm sure they noticed the recoil.

I believe Jagermeister stated a good statement, people think 2 1/2" shells mean low pressure-low velocity, why would it, it's just a shorter shell.

Also firing a 3" shell in a 2 1/2" chamber, idiotic for one and even though it was a test and nothing happened, you can't tell me recoil wasn't greater. First of all the 3" shell had more powder and more payload of shot than a 2 1/2" shell.

JayCee, your picture of the blown barrel, I don't reload black powder but the difference between the two powders is probably 3-1, so he used approximately 100 grains of smokeless, talk about excess, he's lucky.

David