doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 20 ga 2 1/2” reloading data

I was fortunate enough to buy an in proof 20 bore Harkom boxlock at the Southern this spring with excellent wall thickness. The gun is currently with my gunsmith having some cosmetic surgery. Mechanically it needs nothing. However it is a 2.5” Damascus gun. So at long last now that I am retired I am going to take up reloading my own shells.

An experienced reloader friend has set up my new MEC Size Master for me and taught me the basics. I have been reading and researching the process and feel comfortable reloading 2.5 “ Cheddite hulls using a formula provided to me by BP using Winchester powder. I have a good supply of plastic RST 20 bore hulls and I purchased some primed Cheddite 67mm papers. However, I am hoping to find a bigger variety of recipes utilizing other powders.

Published data for reloading 2 1/2 inch 20 gauge shells appears to be very scarce. A friend shared with me the 16 gauge society’s low pressure reloading file and it is robust. I wish I good find a similar resource for low pressure 20 bore reloading.

Any words of wisdom from the group here?

Thanks,
Dr. P

When you find it, please let me in on it. My 2.5 inch 20 ga Trojan needs similar fodder.


To be fair, I don't think a lot of people have spent much time on developing 2.5 inch 20 ga loads.

Low pressure 2 3/4" loads and roll crimp for the 2 1/2" hull. Or if you have old 2 3/4" Win AA hulls which are no where near 2 3/4".

If you decide to use 2-3/4" AA hulls, I have a 3/4oz LP load with 20/28 that I used in my 2-1/2" damascus flues.

I reload for my 2.5-inch chambered 20-gauge Army Navy. I use straight-wall hulls (mostly Cheddite but also Fiocchi, Federal) cut down from 2.75-inch hulls, Cheddite primers, and roll crimping. I have had a number of loads tested by Precision Reloading. The most useful series I tested used the above components, WSF powder, and BPI brush wads (I now substitute BPI SG20-S wads to avoid lead fouling). I tested shot charges of 3/4 and 7/8 ounce, each with 14 and 16 grains powder, for a total of 4 loads tested. Pressures varied between 5K and 8K PSI. I would be happy to forward the full reports if you PM me your email address.

Thank you Hooky….PM sent!

Dr. P

I concur with Eddie. Roll crimping 2-3/4 data into hulls cut down to 2-1/2 is definitely the way to go.

I drew the max pressure line at 8,000 PSI, when picking data to try.

I should add most2-3/4 in 7/8 loads can be roll crimped with cut down 2-1/2 hulls.

If lower pressures are your goal for your 2 1/2" chambered 20 ga, then I agree with using straight walled hulls and wads made for them. (Save your WAA Winchesters for your modern guns.) You also want slower burn rate powders. 20/28 is the most readily available powder. If you have it Unique or Greendot they are very good options. Cheddite, Remington STS, or Winchester 209s are your best option. If you are using once fired hulls, you can trim them down to 2 9/16" and use 2 3/4" data in them. Simply add an overshot card atop your shot column before the initial crimp process and star crimp the edges of the plastic hull to hold the overshot card in place. We refer to this as the "Hartin Crimp". I have reloads on my shelf with these crimps that are 10+ years old and they still have not opened. Its a much faster process than roll crimping and only requires you to make or buy the cutting tool. The results are not as pretty as a roll crimp, but they are very functional.

What constitutes a low pressure load in 20 ga? Good question. I would think anything under 10K PSI. Remember, the smaller the bore the harder it is to keep pressures low. We strive for service pressures under 9600 psi in the 16 bore. Since you have our data you can used it as a starting point, Especially the 7/8 and 3/4 oz loadings. You will need to drop the powder charge a tad as well. But at least it will give you a starting point.

Like you I have added a couple of 2 1/2' 20 bores to the collection recently. I am working up some loads for them as we speak. I have tested a few in my fluid barrel guns. But I haven't sent them out for pressure testing yet. I used the hartin crimp on them. One thing I have noticed about british 2 1/2" 20 bores is that the steep forcing cones do not like hulls with high brass (especially the federal hulls-- which, by the way, are one of the best and easiest reloading 20 ga. hull). So I recommend you only use low brass hulls in your reloads.