doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 2 3/4" in a 2 1/2" Chamber

Thank you. I am simply trying to understand, to get a minds eye general understanding of what is taking place after ignition. I am sure we are all(well almost all) struggling with the concept of barrel bursting every time we see a picture of one. We all like our fingers and want to keep them intact.

I already have an understanding but each time I see a picture of a barrel burst I need to rethink it so I don't wake up in the middle of the night with a bad dream. Often in life there is one small piece of information that is missing in our knowledge base that causes things to go wrong. An example of this might be a stepped end of a chamber in a barrel designed for brass shells. Now, I have heard about this and I may even have a Parker that has it but I am not even sure if there is such a thing. Easy enough to find out before I shoot the Parker again but if you never heard of this kind of thing you would have no reason to even think about it or the safety issue that might develop. Clear as mud but I think you know what I am getting at.

Notable quotes;

"You don't know what you don't know" by an NTSB employee

"The only thing to fear is fear itself" by FDR

Maybe a balance of the two is a good place to be.

Builder;
Stepped chambers did indeed exist, & for paper shells also. I am not personally knowledgable as to whether or not Parker used then. Greener discussed them & stated shell lengths were not controlled close enough to provide the desired advantages & they left a stress point & also were hard to clean right at the point of the stress riser. They are most apt to be encountered on extremely old guns & any gun of this age should be given a through examination prior to firing with anything, even black. This is certainly not meant to imply they should never be fired, only to proceed with utmost caution. I would certinly think one of these guns chambered with a sharp step should never be used with shells having a longer than chamber fired length, even though they were shorter in their loaded length.

I suspect an 1879 Parker hammer underlifter G grade equivalent (I think) with .750 bore diameter that I was shooting with 2 1/2" shells. It has been in the safe for a while waiting for a cast of the chamber. Just have not gotten around to doing it. Too many things to do right now. It is all original and in very nice condition so it won't be changed but it seems important to find out for safety reasons. Thanks for the reply.

Milt

I have two 65mm chambered 16s. One of them weighs 5# 11 and I shoot reloaded light 2-5/8" 7/8 ounce and light 1 ounce factory loads in the gun. I don't see any difference in the fired shell relative to another gun with factory 2-3/4" chambers. I am considering lengthening the chambers in at least one of these so that I can feel better about using 1-1/8 ounce loads for pheasant.

These guns were purchased used and I'll bet they have been used a fair amount with 2-3/4" loads. Not everyone reloads or buys RSTs.

Recently there was a lengthy discussion of forcing cones and lengthening them. I believe that reaming a chamber has the potential to thin the barrels in the most dangerous place while lengthening forcing cones does not. That is not intended to imply that lengthened forcing cones have any real value. Are these guns from England? If so reaming the chambers invalidates the proof while forcing cones is a grey area. If they were my guns, I would not ream the chambers, but find suitable low pressure loads commercially even if they're 2 3/4.

I just found this thread that goes back over a decade, very informative debate.

I remember when this thread was active, and when I just reread it a thought came to mind that was not directly addressed. There are a number of 2.5” originally chambered guns that have had the chambers lengthened and reproofed in England. My thought is just because they have been reproofed for the longer chambers should modern 2.75” ammo be used? If pressure is the primary factor, are shooters mistaken in the notion that 2.75” chambers can accommodate modern ammo? Seems like if a gun was originally proofed at 2.5” with the associated pressures of that shell nothing has been done for the sake of safety, particularly when metal has been removed from in front of the chambers. I’m convinced low pressure in 2.75” shells is probably better than removing barrel wall even if the gun is reproofed. If the gun has had the chambers lengthened and been reproofed lower pressure ammo should still be used.

The Internet and forums on the Internet are not reliable sources for much valuable information. So I will add to that with my own experiences.

I used to visit with Bill Heckman when he had his shop in Livingston, Montana, about Damascus guns and how strong they were. He told me how they proofed guns and and I was amazed at how simple that process was. They put the gun in a brace and test it with their proof loads that are developed for proofing guns at a pressure above what the gun is actually designed for. II the gun didn't blow up, it was in proof.

I took several Damascus guns to him to get his opinion on shooting them with smokeless ammunition and what to expect. He told me that the good Damascus guns were as strong and even in some cases, stronger than the fluid steel barrels of the same era.

Since then, I have shot lots of older shotguns with Damascus barrels and had no issues at all. Before doing so, I did check to see they were in good working order with good wall thickness in the barrels and no rust or pitting.

I have shot plenty of 2 3/4 inch shells in my Webley SXS that has 2 1/2 inch chambers and had no ill effects at all. I do keep plenty of 2 1/2 and 2 inch shells around and shoot them exclusively in those shorter chambers as that is the best way to shoot them.

I have seen blown up shotguns that were from other reasons than 1/4 inch difference in shell length. The best rule of thumb is to shoot what you are comfortable with and if you are afraid of blowing your gun up, by all means use shorter shells.

I would also bet that the pressure is less likely to damage the gun as much as recoil would shake it loose.

shrapnel: IMHO there are many on this Forum with the bona fides to provide accurate and reliable information
Actual strength testing of pattern welded barrels
https://docs.google.com/document/d/1cvqRzkg0wEjhAAcFWr8gFi7aPFRsSIJ_hahfDxmrNAU/edit
and vintage steel barrels
https://docs.google.com/document/d/1dnRLZgcuHfx7uFOHvHCUGnGFiLiset-DTTEK8OtPYVA/edit

eeb:
John Brindle, author of Shotgun Shooting: Techniques & Technology published a review of Proof and Service pressures in Part 5 of his series in The Double Gun Journal, “Black Powder & Smokeless, Damascus & Steel”; Volume 5, Issue 3, 1994, “Some Modern Fallacies Part 5”, p. 11.
His estimated post-1954 but pre-CIP standard pressures by LUP converted to piezo transducer PSI

..............Standard Service.....Max. Service.....Proof
12g 2 1/2”.....6,800 psi..........8,800 psi..........12,250 psi
12g 2 3/4”.....7,800 psi..........9,800 psi..........14,050 psi

Great Britain adopted the 1969 Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives standards March 1, 1980 but continued using Lead Crushers to measure pressure until 1989.
The CIP transducer “Maximal Statistical Individual Pressure” is 850 BAR = 12,328 PSI for a “Maximal Average (Service) Pressure” of 740 BAR = 10,733 PSI, and “Mean Proof Pressure” of 930 BAR = 13,924 PSI.
900 BAR is for a “Maximal Average (Service) Pressure” of 780 BAR = 11,313 PSI and Proof pressure of 1020 BAR = 14,794 PSI.