doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 20 Gauge Pressures and Chamber lengths

One plus about chamber reducers is the extra metal they bring to the chamber area. It can not hurt to have more. I have been shooting full length tubes in Skeet guns for almost fifty years and am very comfortable with them. The chamber adapters are just a shorter version of them in many ways. Like the old Super Tubes used in Brownings in the 1960's. So a proven technology. Those tubes only ran 1/2 way down the barrels and the barrels never suffered any ill effects from them. It is a little odd that velocities are reported to increase with chamber adapter use and that is attributed to less friction between the wad and bore from a looser fit.

I would say 'No'. British 20 bores have a standard load for the 2 1/2" cartridges of just 13/16th. ounce and are quite mild in pressure against U.S. made ammo. Most U.S. ammo is designed to fire in semi-autos and the pressure needs to be higher to cycle the action. You would just be straining the gun beyond what it was designed for. In the 1970's Winchester cartridges were imported from the States and it was found that the popular Winchester AA clay round with 1 1/8th. ounce actually approximated what was only suitable in English guns proof tested to the 2 3/4 inch Magnum proof. Our Winchester stuff is now made in Italy to CIP standards. I still have a few boxes of the old U.S. made Winchester 'Upland' but will only use it in continental guns to 900Kgs. proof. Your option but not what I would do myself. Lagopus.....

Points to note:
If the Super X shells are the discontinued Compression Formed hulls the working pressures will most likely be at the high upper end compared to other US and Euro hulls.
What is dram equivalent of these shells and the payload?

What is the weight of the gun you are going to fire them out of? And if a vintage gun, perhaps you should measure chamber cone diameter and length.

Back in the day, after plastic cases were introduced by Eley - the factory changed many of their product range of traditional 2 1/2" shells to 2 3/4" hulls but designated as suitable for 2 1/2 " chambered guns. This was presumably to facilitate their producing crimp closure shells. Doubtless these were developed and tested to achieve the appropriate pressures for the shorter chambers.
(I recall seeing some pretty poor quality Eley factory loads in 16 gauge - including cork overshot wads underneath the crimp closure.) There were a few instances of guns with short cones or very sharp step to bore "shooting loose" ie needed re-jointing.
The barrels of your gun is likely to withstand the Super X pressures but if you intend to shoot many of them out of a lightweight s x s 20G you better expect to be asking the readership who would they recommend to rejoint the gun or do stock repairs.

Most vintage Brit 20s are proofed for 7/8 oz. loads. Most 16s are proofed for 1 oz. loads. I load for 2-1.2" 12, 16, and 20 bore Brit/Scottish guns.

I am often too lazy to trim hulls, reset loading machines, etc. to load true 2-1/2" hulls. Often I simply load my Win AA CF hulls with recommended 1-1/16th oz. (12 bore), 1 oz. (16 bore), or 7/8 (20 bore) loads. I just keep pressure under 8000 PSI or equivilent CUP and shoot away. My Atkin, Harkom and Robertson guns have never had a problem with this approach. IMO, Hull an additional 1/16" hull length is much less important than pressure and charge weight.

I would say that velocity and charge weight would be more relevant factors in "loosening" a gun, pressure less so albeit indirectly.

When you're speaking of 1 1/8th oz "clay" rounds, you must be talking about 12 bore shells, not 20 bore. In the 70's, the only clay sport one would have been playing in the States was skeet. And for 20ga skeet competition, loads are restricted to just 7/8 oz shot. There are 1 1/8 oz 20ga shells in 2 3/4" hulls, but they are what we call "short magnums" on this side of the pond. They're heavy duty hunting loads, not target loads. And I can't imagine anyone shooting them in a light 20ga with 2 1/2" chambers. There are "heavy" 1 oz target loads for the 20ga, which someone competing in registered skeet shooting might use if they're using a 20 bore in 12 bore competition.

We also have the CIP approved Winchesters made in Italy on this side of the Pond. I haven't shot any of them in 20 bores, but I shoot them regularly in 16 bores.