Ok school me on chamber size

[wankerjake]

Question #1: Why is it that 3" shells should not be shot out of 2 3/4" chambers, when they do in fact fit. Seems to me that the longer shell would just open up into the barrel and the explosion is happening in the same place in the chamber...but there must be a reason. Chamber pressure maybe? Somebody on this site knows!

Question #2: S&B and RIO shells have a different crimp than most shells and their "2 3/4 inch" shells are pretty close to 3" long. Again, the only thing I can think of is more powder and higher pressures with 3" shells...

P.S. I'm just looking for an answer, I'm not gonna try and shoot 3" shells out of my 2 3/4" chamber. I've got plenty of correct ammunition to use, so don't start flaming me. I was just noticing that 3" shells fit comfortably in a 2 3/4" inch chamber, and I can't figure out why. Wikipedia did't tell me.

 

[Whitman31]

I think the problem happens after the shell is fired. The excess length makes ejection problematic. This is my best guess, kinda curious to see what other answers there are.

 

[scythefwd]

The 3" shell is only 3" after it has been fired. The too long shell gets pushed into the throat as it uncrimps and creates an obstruction. The wad then has to squeeze past that restriction in order to make it down the barrel. It might make it, it might not. The 2.75" shells do not extend into the throat (forcing cone???) when fully extended so they don't create that problem.

 

[Blakenzy]

Question #2: S&B and RIO shells have a different crimp than most shells and their "2 3/4 inch" shells are pretty close to 3" long. Again, the only thing I can think of is more powder and higher pressures with 3" shells...

Yeah, this also has troubled me before. 2 3/4" shells that due to the crimp approach 3" length. I have used them but then again I only own 3" chambers so no problem. But what if I had a 2 3/4 only?

 

[scythefwd]

how close to 3" is pretty close?

 

[wankerjake]

Ok I measured some shells (both sizes) and they are all shorter that 2 3/4" before fired. So as scythefwd said, the shells are 2 3/4" and 3" after being fired, or before loaded. The length refers to length of shell, not loaded cartridge. Makes sense now, thanks guys. New it had to be a simple answer

 

[oneounceload]

The excess perssures created by firing a 3" in a 2-3/4" chamber MAY make a gun go kaboom.

The real danger is in older guns where the chambers were 2-1/2 or 2-9/16 and people use 2-3/4. Not only too long, but modern shells are loaded to higher pressures.

Then you get the person who takes an older gun and reams it out to 2-3/4, removing precious metal strength from right where the gun needs it most.

Like any mfg. there are tolerances, but they are minute. 70mm = 2-3/4"