doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Does Roll Crimping Solve Short Chamber Issues?

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?