Would roll crimping shotshells substantially reduce the pressure buildup from the crimp unfolding into a short chamber? Roll crimping is way shorter than fold crimps...Steve

After firing a 2-1/2" shell that is pie crimped is the same length as a 2-1/2" shell that is roll crimped. You should be able to get more stuff in the roll crimped cartridge but with modern dense powders excess room is usually the problem.

I am a member of 16 gauge reloaders group. As I remember what I read there a roll crimp adds about 1000 psi over a pie crimp.

Best,

Mike

No, it is the fired length that counts.

Joe is right


the length is the length - and it is measured unloaded - new or fired

the type of crimp may affect the finished length -

and most data I have seen is that a roll crimp -all else being equal- slightly reduces pressure

I believe Sherman Bell mentions this in his DGJ articles on short ten loads

added- on page 30 volume 12 issue 1

You may also consider the effect of the over shot card on your patterns. They can be affected for the worse.

I believe Mike misquoted himself. Roll crimped loads generally reduce pressure compared with the same load if it were star crimped. For a moment I thought it was a post by ArmadilloMike.

Humph!

Roll crimping allows maximum volume for the load (powder, wad, and shot) for a given hull length (fired length!!). Both the 2 1/2" and 2 3/4" hull lengths existed before the rise of star/pie crimping. To match the usual 2 1/2" loads with a pie crimp shell it was "necessary" to go to the 2 3/4" hull, but not to load the heavy loads they have volume for if roll crimped.

The use of known low pressure pie crimped loads in 2 3/4" hulls in 2 1/2" chambers is well documented. If the load is of "low" pressure, there is no objectionable pressure increase from the 2 3/4" crimp opening into the forcing cone of a 2 1/2" chamber. This was well documented at the time of introduction of 2 3/4" pie crimps as more or less "standard" fare. Unfortunately, said documentation seems to have fallen out of common/street knowledge. The advent of interest in shooting Brit/Continental game guns has led to the rediscovery/reinvention of this knowledge. Always keep in mind that SAAMI (USA) loads allow higher pressure than do CIP (Europe). The taboo of 2 3/4" shells in a 2 1/2" chamber has, or at least should have, more to do with the higher allowed SAAMI pressures than with the hull length difference.

DDA

There's the long shell/short chamber wisdom, in a nutshell. Per Bell's tests, reported in DGJ, a longer shell in a shorter chamber will result in SOME increase in pressure, usually several hundred psi--some of which can be offset if the forcing cone is lengthened. But the major issue is not the length of the fired shell.

I have a question about these tests. Did Bell use plastic or paper hulls, or both? Shot cups or felt/fiber wads?

I believe he was using plastic hulls and wads with the nitro loads and paper/fiber with the black powder.

HD,

He used Federal and Estate (thinner) plastic hulls with a fiber base-wad, fast burning Clays powder, and a one-piece plastic wad.

JC

Thank you. I though so. Could be interesting if the tests were reproduced with nitro powder and paper hulls. I mean, the warnings of not using long hulls in short chambers couldn't appear out of the blue, and paper shells, being thicker, could have a more marked effect in pressure raising.

After reading Mr. Bell's results I started using 67mm plastic shells loaded to CIP standards
in my Manufrance Idéal with 65mm chambers, proofed to 1,100Kg.
I only recently lengthened its forcing cones and have not yet tried it, but I expect a slightly
lower felt recoil, (though I am not sure I'll perceive it).

JC

HD,

Sorry for the partial answer. Mr. Bell also tests paper hulls (Federal) loaded with one ounce of lead shot,
Clays powder, and a one piece plastic wad.

His results show a lower increase in pressure than the plastic hulls. 602 psi increase at the breech and also at the cone.
As he says, "not enough to worry about". The same test with the longer forcing cone reduces the pressure increase
to less than 100psi at one inch and 100psi at the cone.

JC

He used a variety of hulls, both plastic and paper, and wads, both fiber and plastic. Win AA and Rem hulls as well as Federal. See DGJ, Winter 2001.

Does Sherman Bell have any books printed or just DGJ articles?

Jerry

The original tests on this subject were run many years ago with the introduction of the pie crimp hull. The result was as Rocketman has already stated that virtually all factory loaded pie/fold crimp shells were/are longer than the short chambered guns, "Including Those Certified for use in Those Guns". These tests were all run with paper hulls & card & felt wadding. Bell just re-invented the wheel, it had all been established beginning in the late 1930's & completed immediately following WWII, by the end of the 1940's.
As to the length of the shell in relation to the chamber proper use of a shell longer than the chamber dictates a shell having a pie crimp & a "Loaded Length" very close to a roll crimp hull of same length as chamber. It is decidedly un-wise to fire roll crimp shells in a chamber shorter than the shell, especially if the shell is long enough the end of the loaded shell will be forced into the cone Prior to Firing.

PS; If you want a book which thoroughly discusses this along with about anything else you want to know concerning a shotgun get "The Modern Shotgun" by Burrard

I'd submit that Bell did more than just "reinvent the wheel". Like maybe proved that radial ply tires are a good idea. Indeed, early tests on longer shells in shorter chambers were done with paper hulls and fiber wads. Bell conducted tests with plastic hulls and wads--which meant that those who stated "but those weren't modern plastic shells" no longer had a leg to stand on.

Sherman Bell generated data.

My Ideal with 65mm chambers will not go into battery with anything other than a 65mm shell; reloads must have a perfect crimp. The rising bite that engages the doll's head will stop short of coming all the way flush with the doll's head, with the result that the triggers will release, but the hammers are somehow impeded, resulting in light primer strikes. The first time I took the gun to Kansas for pheasants, my spaniel had worked hard tracking down a wily rooster. She put it up, and I swung on it, only to hear "click...click." My shootin' buddy declared, "I never did like French guns." Don't think my dog did that day either.

Mike

There are some guns--not many, and most are older with very short and sharply angled forcing cones--that either won't work or won't work well with shells that have a fired length longer than the chamber. It's rare to find guns with true 65mm chambers that won't accept 67/67.5 mm shells, because that's the FIRED length. They're shorter than 65mm unfired. The more typical problem is, they'll fire but you'll end up with blown ends on the shells. Charles Fergus, for one, reported that problem in Shooting Sportsman. The slightly longer hulls worked fine in a between the wars Brit gun with short chambers, but he got blown ends and also stated a louder report and more recoil in a 19th century gun. Chambers the same length; forcing cone different. He reported that true 2 1/2" shells worked fine in the older Brit gun.

Older SAAMI Specs for the 12 gauge 2 3/4" chmaber specified a minimum length of 2.614" length with a minimum diameter of .798" to a minimum cone of 5° per side. To a standard size bore this will give a cone length of about .400". At 2 3/4" this also gives a diameter in the cone of .774" or .024" smaller than the chamber end. These specs were in effect well beyond the introduction of the 1½ oz 12ga "Short Magnum" load. This load should have of course been used only in those guns of later manufacture designed & proofed for the heavier loaded shells, but the problem with the older guns was not as a rule in the chamber dimensions themselves, but the overall strength of the gun.
"ANY" gun with its chamber ending in an abrupt step or cone of extremely short design should of course never be fired with a shell longer than its chamber. Certainly not one in which the crimp upon opening will extend up into the bore itself. Also no gun should be fired with a shell long enough in its "Loaded" length to actually enter the cone. As to the gun with 65 mm chambers which will not properly close with a 67/67.5 mm shell, you have some problem other that the length of the shell. As Larry correctly pointed out the loaded length of that shell will not extend to the end of the chamber, it will only do so after firing.

Had exactly the same situation here, with a Russian hunter to whom the late Geno told about Bell's experiments and that it's OK to use 70 mm shells in 65 mm chambers. The hunter experienced increase in recoil and blown heads; the shells were hand-loaded with roll crimp and were identical to the load which worked fine in 65 mm shells, except for the length and an extra fiber wad.

The use of a roll crimp in this case certainly exacerbated the problem. The roll crimp shell has a longer "Loaded" length than a fold crimp one having the same fired length. If in the case of this gun it had an extremely short cone the loaded shell may well have actually been pushed into the cone upon loading. This would in effect give a much stronger crimp strength, delaying its opening which can give drastically increased pressure.
The firing of a longer shell than the chamber length is dependent on there being clearance between the end of the loaded shell & end of chamber. It is further dependent on the end of the shell only lapping into a cone of normal length & not a very short cone which would allow the shell to reach either into or almost to the bore itself.

Interesting, all. I had thought, by looking at the spent hulls of slug loads, that roll crimped hulls were shorter. If they are not, then no, they would not properly expand into the 2 9/16 in. chambers. Thanks for the education, as usual...Steve

Steve;
Note that the length of a hull is determined by its New/Unloaded/fired length. Thus the type of crimp itself has no bearing on the length of the hull. Once loaded though the fold crimp uses more of the hull in crimping thus has a shorter loaded length than does a hull starting at the same length but roll crimped. In fact a 65mm (2 9/16") roll crimp & A 70mm (2 3/4") fold crimp shell will end up as loaded having very close to the same loaded length. Thus either of these shells will have a bit of clearance between the end of the shell (loaded) & end of chamber. How ever "IF" you take the 2 3/4" hull & roll crimp it the loaded length becomes longer & that chamber clearance is encroached upon.