doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com How to tell 2 1/2" chambering from 2 3/4"?

I used the index card method mentioned until I finally got a gauge. I see everyone covered everything so now woohoo! Kudos on getting a greener and getting one at an honest deal. Great job! I would love to see more of it

Do note that upon the introduction of the fold crimp, just prior to WWII the British began experiments with shells longer than the chamber. They were mostly halted by the war but resumed immediately afterward. From that point onward virtually all British 12 gauge shells marked as suitable for 2�" chambered guns were actually put up in a longer hull.

Bell brought this to the attention of a lot of shooters, but to be totally correct in giving credit where credit is due, he neither Discovered it nor Invented it. This fact had been long settled likely before Bell ever pulled his first trigger.

I don't know just how old Bell is but in less than a month I'll be 81 & this was all "Laid to Rest" before I turned 12.

Do note a couple or three things though.
No shell should be fired in a chamber in which the loaded shell has to be pushed into the cone, it is essential there is clearance between the end of the loaded shell & the cone to allow proper opening of the crimp without restriction.
Also no shell longer than the chamber should be fired in a chamber having a step or extremely short cone which lets the end of the shell actually lap into the bore itself. It may or may not burst the chamber but is certain to increase the pressure drastically.
Finally, the longer shell should only be loaded to the pressure level the gun was designed for. This harks back to Rocketman's warning.

It was certainly discussed in British literature, although mostly forgotten on this side of the pond. Gough Thomas' "Gun Book" includes a chapter called "Danger in Case Length", which dates from October 1964. Burrard made reference to the same thing earlier than that. The Thomas article even includes a test he arranged to have run by Ely, firing 2 3/4 shells approved for guns with 2 1/2" chambers in test barrels chambered both 2 1/2" and 2 3/4". Pressure was measured in tons per square inch (standard Brit measurement at that time) at 1" and 6" from the breech, and observed velocity (average over 20 yards, also Brit standard at the time) was also measured. 10 shots were fired in each test barrel. Differences in both pressure and velocity were minimal between the two test barrels.

�Mr. Griffith on Shotgun Patterns�, 1897
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA234

p. 243 �Turnover� � case longer than the chamber
No. 9 2 1/2� case with 1/8� turnover
No. 10 3/8� turnover
No. 11 & No. 12 with 2 3/4� and 3� cases in 2 1/2� chambers = ��patchy patterns, clustering, and frequent balling�� Pattern examples on p.244
p. 245 �balling or clustering�
p. 247 �Summary of patterns�, Field, March 5, 1898
No. 9 - 1/8� turnover better pattern % than 10, 11 & 12

Pressures with 3 Dr. �Schultze� with 1 1/8 oz.
(pressures converted from long tons/sq. inch to psi by Burrard�s formula)
2 1/2� case with 1/8� turnover � 2.13 tons = 6,040 psi
2 1/2� case with 3/8� turnover � 3.03 = 9,060 psi
2 3/4� case in 2 1/2� chamber � 3.22 = 9,700 psi
3� case in 2 1/2� chamber � 3.71 = 11,345 psi

�When long cases are used in short chambers, the paper overlaps the cone and causes greater resistance to passage of the shot and wads. The pressure then goes up considerably, while muzzle velocity and recoil are both increased.�

That is essentially what I said Larry. The British had resolved the matter at least by the end of the 1940s. Burrard essentially made two statements concerning chamber lengths for which he has been accused of issuing conflicting statements. This accusation came purely from the lack of understanding the statements were made at different times & pertained to different circumstances.

In his first statement, he emphatically advised against firing a shell longer than the gun was chambered for. At the time this statement was made it was entirely correct due to two circumstances. First, it was made at a time when shotshells were closed with a fold crimp. A 2 3/4" shell in a 2�" chamber is apt to extend into the cone "Before" firing which should not be done for the reason stated. The second factor was at that point in time the 2 3/4" shells were loaded heavier & for a gun carrying a heavier proof. When the fold crimp was developed & the British gunmakers & ammunition loaders set out to determine if the hull could within safety factors be lengthened without lengthening the chambers it was proved to be feasible. Burrard gave full coverage of this new factor.

I have read both Bell & Thomas' accounts & for whatever reason, neither seemed able to comprehend this & strongly "Implied" it was totally unknown until they brought it to light. This is about as absurd as trying to say that Samuel Colt "Invented" the Revolver. Colt did at least "Improve" the revolver, which is what his original patent stated. All either Thomas or Bell did was to state some facts which had already been proven for at least a decade & a half prior to Thomas' 1964 work & far longer before Bell took it up.

I acquired a copy of Burrard in the 1960s & I knew this before I ever heard of either. I had no problem at all understanding the two different accounts Burrard made nor any problem separating them from one another. They very clearly applied to different circumstances & were written at different points in time, which he made quite clear.

Yes, I have read Bell and others (much like Miller). I am less worried about the barrels than the stock and the barrel-to-action jointing. Barrel failures are very low % probability, but can be catastrophic for the gun and/or shooter. Stock and jointing failures are mostly cumulative over time/shooting cycles, but are costly (maybe too costly for a less expensive gun). There is very sufficient information available, thanks to sites such this, to feed old guns properly.

DDA

A few comments; First this reflects what Burrard originally said & was the truth as stated. These shells would have all be roll crimped/Turnover. The increase in pressure of the 3/8" turnover above the 1/8" turnover shos the pressure rise from an increased crimp strength. The amount of turnover is not stated on the 2 3/4" shell but as not otherwise stated it can I believe be safely taken as the normal 1/8". This allows the end of the unfired shell to enter the cone of the 2�" chamber thus effectively increasing Crimp Strength & even more so on the 3" shell.

What was later proved was that if the normal 2�" load was put in a 2 3/4" case & then closed with a Fold/Pie crimp, the loaded shell was essentially the same length as the 2�" shell closed with a roll crimp. This allowed adequate room for the crimp to open, un-restricted & pressures were then "Normal". In a normal length cone, the slight overlap of the "Fired" shell was not enough to create an undue restriction. This, of course, does not apply with those stepped or unduly short cones in which the fired shell would actually lap into the bore itself. This was all well reported on my Burrard who incidentally made no claims as to having "Discovered" it. He simply reported on the work which had been done by "Professionals" in the ballistics field.

The two main factors thus were The "Load" had to be compatible for the gun it was intended to be fired in (R'Mans Concern) & the Loaded shell must be shorter than the chamber allowing freedom for the crimp to open normally.

Not really that hard to understand.

Miller you have to give to the dOc he does a great job of copy and pasting...

Miller, I know you don't care much for Thomas. But to give him his due, I think you need to reread what he wrote. Concerning Burrard, here is what he had to say. Note that he clearly gives Burrard credit--making clear reference to the longer shells containing a heavier load:

"Burrard leaves no doubt in his readers' minds that the danger in question arises from the inability of the longer case to open up properly in the shorter chamber, and the higher pressure generated by the constriction thus formed. IT CANNOT BE TOO STRONGLY EMPHASIZED THAT IT IS INDEED DANGEROUS, IN GENERAL, TO USE CARTRIDGES WHOSE UNLOADED CASE-LENGTH EXCEEDS THAT OF THE CHAMBERS OF THE GUN."

"But in the particular case cited by Burrard, the main danger arises, not from the constriction when the cartridge is fired, but from the fact that the longer-cased cartridges he had in mind invariably carried heavier loads; and heavier loads in a given gun, USING A GIVEN POWDER, of necessity involve higher pressures. It is, in fact, pressure that causes the danger."
(Emphasis Thomas.)

For those who remained concerned (for whatever reason) about the danger of British shotshells loaded in 2 3/4" hulls but designed for guns with 2 1/2" chambers, Thomas then goes on to publish the Eley test results, which show scarcely any variation in either pressure or velocity, whether the shells were fired in a barrel with 2 1/2" or 2 3/4" chambers.

Larry; Can you point out any part of this post which is Untrue. I just try my best to state facts as they have been revealed.
As to Thomas, I will just say that You & I didn't read the same book, in the one, I read he definitely did not quote Burrard & strongly implied this fact was unknown until "HE" proved it. Burrard made no claim as to having proved this fact, only stated what had been proved by the Expert Ballisticians of the ammunition companies of GB. Actually, a co-worker loaned me his copy, don't at this late stage recall the exact Title or date, but He Said "Burrard Should Have Said & then proceded to say exactly what Burrard did say. When I returned the book it was offered to me at a good discount but I declined He was a very knowledgable person on guns & was unlike me, an "Engineer (Mechanical, not Civil) & also found it worthless & put it up on eBay I believe.
End of discussion on my part, I am not going to be drawn into another long drawn out multi-page discussion with you on anything. Seems most everyone here by now Knows you & how you will twist everything around & When (not IF) you are proved wrong you will even try to take credit for what was proved to you showing you were wrong. BYE