doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Long shells in short chambers, part 2

OK. Now you have a modern steel american shotgun. Let's say a 1960 Mod. 12 trap gun that's chambered for 2 3/4". I think all would agree you can safely shoot modern 2 3/4" and even the hot 2 3/4" magnums in it.

How about shooting 3" modern shells in same? Is that OK?

Isn't that the same situation as shooting 2 3/4" shells in short chambers? Sure the older double guns were designed for lower pressures. But as a few of you think that's not a problem if lower pressure 2 3/4" shells are used in older short chambered double guns.

Dogfox, I am sure several will come along and explain why, but it is NOT "the same situation".

JC(AL)

I think your comparing apples to oranges.
I shoot LOW PRESSURE 2-3/4" shells in my short chambered guns.
I think a 3" magnum 12 gauge load is already pushing the upper limits of SAAMI max. pressures. So, you would stand a pretty good chance of pushing it over the PSI limits by shooting it in a 2-3/4" chambered gun. However, it's your gun.

are you using low pressure 3" reloads? If so, and the forcing cones are not too steep, you will be just fine. I know thats not the answer you were looking for, but its true. Pressure is much more important than 1/16" of hull length. Lots of 67mm euro shells out that the maker states are fine for 2&1/2" guns, one fired they are about equal to our 2&3/4" hulls. I like the safety margins of my handloads in 2&3/4" hulls just fine.
Steve

SAAMI max service pressure is the same for 2 3/4" and 3" 12's: 11,500 psi. However, I agree that a factory 3" mag is more likely to be pushing that max than is a 2 3/4" load. And because there is going to be at least a slight pressure increase with the longer hull (per Bell), you might very well exceed it. But in a pump or auto, most likely the greatest difficulty would arise with the ejection port etc. A 2 3/4" chambered gun probably would not cycle properly.

May be I should have written further in my post. I don't have a M12 trap gun. This was a theoretical situation that closely simulates the other thread on Roster's article. Let's say it's a modern single barrel that doesn't have an ejection port issue.

Question, if the M12 or the modern single barrel can safely handle the pressure of 2 3/4" magnums why wouldn't you shoot 3" factory shells in it? I agree, that would be unsafe and stupid, but isn't this the same situation as shooting lower pressure 2 3/4" shells in a double gun chambered in 2 1/2"? If you people are right in your thinking - contrary to the warnings of the ammo makers - there would be a very negligible rise in pressure with the 3" shells.

You can't have it both ways people. Why are you faltering on the 3" in 2 3/4" chamber situation?

No one is faltering, read my original post.
I thought I explained it very well.
I think your comparing apples to oranges.
I shoot LOW PRESSURE 2-3/4" shells in my short chambered guns.
I think a 3" magnum 12 gauge load is already pushing the upper limits of SAAMI max. pressures. So, you would stand a pretty good chance of pushing it over the PSI limits by shooting it in a 2-3/4" chambered gun. However, it's your gun.

Specifying just the length of the shell is vague, to say the least. Mr. Bell is specific about shot charge, powder, pressure, type of shell used, etc.

If you want to argue for arguments sake be a little more specific.

JC(AL)

No faltering. SKB answered your question.

It's about PRESSURE. Many a Enlish and European guns were made with 2 3/4" chambers but were PROOFED for pressures (Ex: 850 BAR) below the SAMMI maximum pressure.

As I posted in the other thread, even SAMMI mentioned in there earliest documents that shell length is unimportant unless it causes a rise in PRESSURE.

I have two English doubles from the 1870-80's with 3" chambers. The additional length was for additional wadding to help with patterns in the days before the plastic wad. They are both blackpowder proofed and in no way designed for todays modern 3" shell. Why not use a modern 3" shell in these guns? Because they were not designed/built to handle the PRESSURE generated by modern factory 3" shells.

When SAMMI came into existance they set shotshell maximum pressures signifigantly higher than most shells of the day. I think Winchester Super X was one of the first examples of shells made to the new higher pressure limit.

With the regular availability of these 'new' higher pressure shells the manufacturers labeled the boxes so that buyers would be aware and not use them in older guns designed/built for lower PRESSURES.

Low pressure 3" shells can be safely shot in a 2 3/4" chamber just as can low pressure 2 3/4" shells in a 2 1/2" chamber. Full pressure 3" shells should not be shot in a 2 3/4" chamber just as full pressure 2 3/4" shells should not be shot in a 2 1/2" chamber. That is not having it both ways, simply having it as it is.

It is the nature of most propellants, certainly the ones used in firearms, that the higher the pressure, the more sensitive they are to factors that raise pressure. The relationsips are non-linear. A low pressure shell would likely have a very small pressure rise when fired in a short chamber. On the other hand, a shell loaded to near maximum may have a significant pressure rise due to being fired in a short chamber.