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

JDW, there shouldn't be any problems shooting a factory 3" shell in a modern American double with 2 3/4" chambers. Why not? Well, because the SAAMI pressure standards are THE SAME (11,500 psi) for both 2 3/4" and 3" shells. However, why would one want to do so?

2 3/4" in a 2 1/2" chamber, on the other hand . . . For one thing, here in the States, 2 3/4" is our standard case length. All sorts of very low pressure reloading data is available for 2 3/4" 12ga hulls--lower pressure, in fact, than the vast majority of the factory 2 1/2" shells available in this country. Not to mention a lot cheaper! So why not use the reloads, to the appropriate pressure standards?

As far as the actual chamber length of a gun with a "nominal" 2 1/2" chamber . . . I have a pair of such guns, marked 2 1/2", and unaltered. Using my chamber gauge, I get just slightly over 2 1/2"--probably less than 2 9/16", and certainly less than 2 5/8".

Some measurements of once-fired American and British shotgun shells, all plastic, all crimp-closed (with a digital caliper):
Remington STS: 2.69"
Winchester AA: 2.70"
Federal Gold Medal: 2.71"
Gamebore Super Game (Nominal 67MM): 2.63"
Eley Blue (Nominal 70MM): 2.59".
Note that the 67MM Gamebore (marked on the box as suitable for guns with 65MM or 2 1/2" chambers) is only .07" shorter, on average, than American factory 2 3/4" hulls. That's almost exactly 1/16th inch--not likely to go very far into the forcing cone.

As for Gough Thomas, I refer once more to his "Gun Book", chapter entitled "Danger in Case-Length"--the conclusion of which is that there isn't any danger in case length. He specifies that the test he conducted used crimp-closed shells in 2 3/4" cases (to pressure standards appropriate for 2 1/2" guns) and had them fired in pressure barrels with, first, 2 1/2" chamber; and then 2 3/4" chamber. NO DIFFERENCE IN PRESSURE OR VELOCITY.

I'm not interested in convincing anyone here to use 2 3/4" hulls (even if loaded to low pressures) in 2 1/2" chambers, unless they wish to do so. I am presenting the evidence, which I find to be overwhelmingly convincing--and from 3 separate sources who conducted separate tests (Burrard, Thomas, and Bell)--that, providing the shell is loaded to the service pressure appropriate for a 2 1/2" gun, the 2 3/4" hull, in and of itself, presents no additional danger.

And Joe, that's a very interesting Parker hang tag. At the time that gun was built (1902), there would have been no difference in pressure between a 2 3/4" and 2 5/8" American factory shell. It was not until the 1920's that the higher pressure, "modern" American 2 3/4" loads appeared. Once more, the extra length would not have made a difference.

Control of "BREECH PRESSURE"is the key safety concern when shooting 2 3/4 shells in British 2 1/2 chambered guns.Quoting from Eley literature they state,"Some 12G,cartridges having 2 3/4cases can be safely used in guns having 2 1/2 chambers!"
If you measure your typical 2 3/4 shell you will find that the actual loaded length is 2 1/4 - 2 5/16. After firing the case length measures 2 5/8-2 3/4. [You will also find that cartridges sold as 2 1/2 have almost the same dimensions as the 2 3/4 shell!]The thickness of a plastic shell case is .020 approx; therefore this 1/4 inch extension of the shell case can easily be accomodated, without constriction below bore size, in the the forcing cone as it transitions from chamber diameter to bore size.
Noted English balistics experts, Burrard and Garwood [Gough Thomas] have published test results that show 2 3/4 shells correctly loaded for the design pressure of 2 1/2 chambered guns can safely be used in nitro proof [In Proof] British guns with 2 1/2 chambers.
I use the following reloads in 2 1/2 chambered guns:-
22.0 Gr.Dupont SR 7625 powder.
Winchester AA Hulls.[or similar 2 3/4 case length shell]
Remington 29930 wad.[or similar]
1 1/8 ozs; shot.
Approx breech pressure is 6900 LUP.

Chuck:

I hope you comment is not a dig.

[quote=... Thats where judgement, based on knowledge and experience, becomes relevant.

Or even better, getting real data. [/quote]

I hope you understand that I wasn't suggesting "wives tale" decision model or anything like that. Experience produces the ability to use judgement, and experience includes the gathering of real data. In this case that measn seeing what the pressure gun says and not listening to cracker barrel "truisms" such as "black powder is lower pressure than smokeless". I am always in favor of real data.

In engineering the judgement part comes in when you look at the data and make a decision as to whether or not the differences make a "hill of beans" or whether a given option is worth the additional cost or risk versus the actual benefit.

regards

GKT

[quote=JDW]
I thought that I had said modern guns when I said about putting a 3" shell in a 2 3/4" chamber. Meaning new guns. I was trying to make a point about using a new manufactured 3" shell in a new modern proofed 2 3/4" chambered gun. To me that is the same difference as what the topic is.

OK, got it. I believe that the data has shown that if both the 3" shell and the 2-3/4" shell are loaded to the same pressure, and the 2-3/4" chambered gun is designed for that pressure, then there will be no significant pressure rise (10 to 15 %, significance is up to the one interpreting the results). But as someone said before me, there really is no motivation to do this because there is no cost or convenience-based motivation. In fact, 2-3/4" shells are easier to find and cost less to begin with. But whatever the outcome or motivation, I must agree with you that it is something we generally don't do.


(JDW:)I must have missed the part where the gentleman was from England, I thought he was from S.C.

Yes, London in fact, according to his profile. And I don't disagree with his view point when I take it in context with where he is from and what he's used to over there, and what he probably meant. But I wanted to point out that there are other guns being discussed than British, and in the end, wall-thickness and condition trump a set of proof marks, especially on guns that never had them.

Also did you get a long beard this morning?

Heh! Well, no. But I did have an enjoyable hunt. We are having a record-setting cold spell this week, and the wind has been up over 20 mph for 3 days straight. I got in the woods among the swaying trees this morning and could hear one gobbler proclaiming the Gospel with conviction. But, he was 100 yds. across the property line roosted on the edge of a field on that property. That was where he intended to go and I could not convince him otherwise. He must have stayed in the tree for over an hour past normal fly-down time, riding the swaying limbs and arguing with a bunch of owls. I had two jakes come to investigate me up to about 15 yds. and I managed to not spook them, and watched them feed away. By 8:00 I was frozen, and packed it in. Enjoyable morning, though.

ONE MORE TIME:
You have to read in the "Context" of which it was written. The part SmallBore quoted from Burrard is in fact totally out of the context to this question. It applied to loading, as he called it, the "True" 2 3/4" cartridge, put up with 1¼ oz shot, a heavier powder charge, higher pressure & at the time he wrote that, in a roll crimped shell which would come about even with the end of the chamber as loaded.
I quoted to you "WORD FOR WORD" exactly what Burrard said concerning putting up the regular 2½" load in a longer 2 3/4" case when the fold crimp replaced the roll crimp. There was NO increse of pressure, Apparently you are totally unable to Read & Understand. This was also borne out by both Thomas & Bell.

Greg,
No, I didn't intend my comment as a dig (no offense intended at Mr. Digory Hadoake (sp) either). If it sounded otherwise, my appologies. I agree with your elaboration. Mine was more from the perspective that "knowledge and experience" was used in terms of previous experience and education applied to the current subject through association and extrapolation. When an engineering issue has numerous factors that influence the outcome, actual testing of the article with all the factors included sometimes is the best way available to assess the issue. (Example: when we build a new airplane, we do hundreds of tests even though we have much knowledge and experience with very similar designs from the past. This is because the interaction of many variables in the design create complexity in analyzing as opposed to testing the actual article) Hence my comment; "Or even better, getting real data."

Sorry 2-piper, but wrong again.

Burrard states on p.175 of Vol III about the crimped cartidge "I doubt whether its use can make any practical difference to the conclusions I have ventured to draw".

He goes on to mention the heavily loaded Eley Maximum cartridge, introduced in 1933 and still available from Eley (I use them loaded with bismuth for duck shooting).

"it contains a low-velocity load 1 1/4oz) ... but at a pressure which is normal for the standard 2 1/2" 12-bore load." (Again- showing case length and pressure to be key rather than pellet load).

On p.162 he illustrates a gun with 1 1/2" chambers used with 2 3/4" nirto cartridge.The barrels burst.

When manufacturers moved to crimp closed shells, they made the nominal chamber length markings they put on the boxes refer back to common proof markings:

I have in front of me a box of Hull 'Imperial Game' 28g 2 1/2" shells. The box states:

"These cartridges should only be used in guns proof marked for a shot load of at least 1 1/8oz and/or marked for a service pressure of at least 3 tons per square inch. DO NOT USE IN GUNS OF CHAMBER LENGTH LESS THAN 2 1/2".

Also, from box of Game Bore Pure Gold; "for 70mm case length; These cartridges are suitable for use in guns with a chamber length of 2 3/4" or longer, nitro proofed to a service pressure of 3 1/4 tons per square inch (900kg per square cm).

Ammo makers load 2 3/4" cartridges to higher pressures and they require higher proof charges to test for them. This is irrespective of the pellet load in the case.

So, the manufacturers say don't use 2 3/4" shells in 2 1/2" proofed guns. I also spoke in person about this with the Proof Master of the London proof house last week. He told me in very clear terms that it was not safe and that 70mm cases should only be used in 2 3/4" chambers.

I believe the message that goes out from here to readers should be 'Use the right ammo in your gun' not 'use the wrong ammo if you like because sometimes it is OK'.

There are issues of public safety here and we should be giving out the right messages. Too many people will come away from reading this with the impression that you can pop into Wallmart, pick up a slab of whatever normal 2 3/4" shells they have and happily fire them off in their 2 1/2" chambered Webley 700 with no ill effects. Bad idea.

I would like to thank L. Brown for confirming that at least two of those 2 1/2 inch chambered British doubles do indeed have 2 1/2 inch chambers. Hopefully, this is true in general.

Well before magnumitus became endemic, 65, 67 and 70 mm hulls were sometimes loaded with an additional 1/8 to 3/8 oz of shot and reduced powder charges. Old loading manuals often include various such loads, generally with pressure data showing normal chamber pressures. I have shot lots of those in older, but still strong, doubles, with heavy loads of larger shot (the ancient low velocity, heavy shot approach for waterfowl, etc.). Don't recall there ever being a fuss about these loads being unsafe in guns designed to hande these chamber and barrel pressures and breechface forces, guns still in excellent condition.

I do agree with Smallbore's concern about an unsavvy shooter using highpressure USA shotshells in an actual 2 1/2 inch chambered, lightweight British double. Do many such folks follow this Board? However, this is a BB where the savvy reloader and shooter can get rather detailed informations about ways to increase the versatility and satisfaction of their hobby. Many of us follow this BB closely for just such informations. So, can there be an acceptable balance of these two concerns?

Niklas

Niklas, Well said and exactly why I posed the question to begin with. I never thought it would develop into such s firestorm of strong opinions.

I do not recall a "Single" person here recommending to go out & "BUY" shells having a higher pressure than a gun was intended to fire, whether of the same or longer length. I did not omit that part of Burrard but you very conveniently keep omitting the part you don't agree with. That's fine, OK by me, but I don't feel I have given out any un-safe info. As I understand it the reason for changing from an "Ounce" proof to a "Pressure" proof was because of the situation you mentioned where a 1¼oz "Low velocity/standard pressure" was quite acceptable for firing in a "Normal" 2½" gun proofed @ 1 1/8oz. Many did not recognize this & thought it not with-in proof parameters. A similar circumstance was the changing of "Not-for-Ball" to choke. The change allowed shooters to "Think-for-Themselves" & realize a ball was quite acceptable as long as it was small enough to go through the choke. If you were to "MEASURE" all the fired shells made since the introduction of the fold crimp, & sold in the British trade in boxes marked "For use in 2½" chambers" or whatever is normal, I truly suspect you would be ABSOLUTELY FLABBERGASTED at just how mny of them were in fact longer than the chamber they were marked to fire in. You simply can't seem to understand we are not talking here of reading boxes, but putting up "Identical" loads in empty hulls by reloading. No one is recommending firing those loads made for higher proofed guns in a lesser gun.