doublegunshop.com - home Forums Thread Like Summary - Loading for 2-1/2" Brit 20b

I recently bought a Robertson 20b with 2-1/2" chambers and am in process buying another 20b 2-1/2" Atkin SLE. I already load 2-1/2" 12b and 16b shells for my Atkin 12 and Harkom 16. I am preparing to begin loading for the short 20b guns.

I have some RST 20b 2-1/2" ammo and paper hulls, but almost all my 20 gauge hulls are WAA 20s - a couple bushels full. I'd like to work up suitable 3/4 and 7/8 oz. loads using the AAs. Measuring the length of fired hulls and comparing the '2-1/2" RSt and the 2-3/4" WAA20s I see that the fired RST paper hulls are 64.5mm long, while the WAA20s are just 67mm long, so difference of 2.5mm or 3/32" between the two hulls types. I COULD cut down the AA hulls but feel that the difference between the two hulls is very small and many "2-1/2 inch' Brit cartridges are loaded in hulls that are 67.5mm long. So I am tempted to simply load a lower pressure load in the standard WAA20 hull.

I am asking those who have some experience with loading for 2-1/2" 20b Brit guns what they do and have they used the slightly longer AA hulls without cutting off the hull by 3/32" ??

Thanks for your help.

C Man

C Man,
I think that Kent has 2 1/2'" loads in 12 and 20 with 3/4 oz. payloads. Perhaps loading the 20 ga. hulls with 3/4 oz. might do it for you.
Karl

A 2 1/2” chambered gun is deemed safe to shoot with 2 1/2”, 65mm and 67mm ammo. It then becomes a question of pressures. CIP 20 loads tend to be well under maximum service pressures. Do a search on this site to go over what a safe pressure load is. For my short chambered 20’s I stick to 9,000 psi as the upper limit. I know by the book that is well under maximum service pressure. With AA and Remington I load near 8,000 and with Federal, Cheddites and Fiocchi I try to get nearer to 7,000. One specific load for each hull type. That way I know every shell is safe in each of my guns the 7,000 psi are great in my Ithaca Flues with 2 1/2” chambers.

Funny thing is 3/4 ounce loads rarely run lower pressure. Most likely they need to keep pressures higher to operate semi auto guns. You would think they could give us a couple 5,000psi loads.

I have shot thousands of 2-3/4 AA hull hand loads through my 20ga 2-1/2 chambered Flues with Krupp barrels. It was loaded with 20/28 at just south of 9k psi.
If you look in the Alliant 20/28 load manual, it is the load listed at 8880psi and 1200fps.
Never an issue.

There is also a 7200psi load at 1200fps with 3/4oz and 20/28 in the manual. It uses a different wad but I've shot some of those with good results as well.

I have a 6400psi load with 11/16 oz of shot in AA hulls that I had Mr. Armbrust test for me years ago if you would like it. Its only running 1075 but breaks clay just fine. I use to shoot it in a damascus Flues 20.

C Man,
I believe that my 2 1/2" 12 Ga. does well with the 2 3/4" shells that are 7/8 oz. 1200 fps is because the difference is so slight and because the plastic hull mouths are so thin compared to the 2 1/2 paper RST's i once shot in it. The plastic hulls show no damage to the mouths.
Karl