I have a 1941 Cashmore sis 20 gauge. I have been seeking low pressure shells for it for a long time with no luck. Would Winchester AA shells at 1200 fps be too hot?

Are the chambers 2 3/4"? Is the gun in proof?

Scroll down to p. 23 here
https://www.appuntidiricarica.com/pluginAppObj_120_24/Winchester-Reloaders-Manual-.pdf
The AA 7/8 oz. at 1200 fps target is listed at 11,200 psi

These service pressures were published for 2 1/2" 20g under the 1896 Rules of Proof; for a max. service load of 2 1/2 Dram Eq. with 7/8 oz. shot (1210 fps)
Bulk “Schultze” - 8,220 psi; “E.C.” - 9,100 psi + 10-14% for modern piezo transducer numbers

A chart published for the 1925 Rules indicated a maximum service pressure for 2 1/2" of 10,100 psi and 2 3/4" 10,700 psi + 10-14%.
The chart did not list standard service pressures but likely about 75% of the max. pressures.

In 1955, under the 1954 Rules (and the pressures were no greater than under the 1925 Rules), Burrard published:
20g 2 1/2” 3/4 oz. 2 1/4 Dr. Eq. standard service 9,632 psi; max. service 12,320 psi
20g 2 3/4” 7/8 oz. 2 1/3 Dr. Eq. standard service 9,968 psi; max. service 12,992 psi

It is a year to year crapshoot with pressures of commercially available ammo. All that is required to satisfy SAAMI is pressure below 12,000 psi with a modern 20 ga. Mfg. ammo changes recipes (and pressure) depending on what's available component-wise. Does the gun require low pressure ammo? If a 1941 Cashmore requires low pressure ammo, then it would be too hot. Then there's the pesky issue of 2.5" versus 2.75" ammo. What's chamber length? Gil

You can usually find "Trainer" loads, they are 3/4 ounce.

https://www.rstshells.com/store/m/4-20-Gauge-SHORT-COMPONENT-TO-MANUFACTURE-/-NO-ETA.aspx

If your Cashmore is a 1941 gun, then it will have been proofed under the 1925 rules of proof. That means the chamber length should be stamped on the barrel flats, along with other proofmarks. A 1941 gun would most likely have been made with 2.5" chambers, although 2 3/4" certainly isn't impossible. But even if it has 2 3/4" chambers, that doesn't mean you should shoot American factory 2 3/4" loads in the gun. US (SAAMI) service pressure is much higher than British service pressure.

The British standard load for a 20 bore for the 2 1/2" chamber gun; which I suspect yours will be, is for a 13/16th. ounce load. Best sticking to European cartridges of that length which have the C.I.P. stamp on the box. We in the U.K. can get Winchester 20 bore cartridges which are the RANGER brand but loaded in Italy and intended for these 2 1/2" guns. It would be interesting if a Winchester supplier over your way could source these. Lagopus.....

3/4 factory ammo will often be loaded at a high pressure to operate semi autos. If you look at Hodgdon website 3/4 ounce, pushing 1200 fps are often 10,000+psi some much higher. We do not know what factory shells like Winchester, Remington or even Federals pressure levels are. But they all operate semis so most likely higher than what we want.

If you reload things get easier since RST seems very limited in production these days. I trim my hulls to 66-67mm which are acceptable for 2 1/2” chambers. I load mostly 572 because they both work well and are available. At my Sporting range I can pickup all the Federal, Cheddites and Fiocchi 20 gauge hulls I want for free. Federal hulls run 7,000-7,500 for 1150fps. Bump it to 1200 and you are still well under 9,000psi. Stack height works well. You can find loads for the others using the same powder. To keep things simple only 1150/7,500 loads go into Federals, 1200/8,500 go into Cheddite and 1150/8,500 go into Fiocchi hulls. High pressure loads only go into Remington and AA. Plus free hulls can be single use hulls if needed, they were free.

I see where one of the two pressure testers that are commonly used by reloaders, Precision and Tom Armbrust, but Precision will no longer test factory loads. It is probably because they don't want to paint themselves in a corner testing shells that often change components and don't want the exposure of a factory load being declared safe when the load tested was not the same as shot by the complaining party . Gil

Gun uses 2 3/4” shells. When I first got it, I was told I could use regular factory shells. Couple of rounds of skeet and the timing got knocked out of whack. Back to the gunsmith and it was returned, all set to go. I was told to not use ‘romper-stomper’ loads’ and did not know enough at the time to ask for more detailed specifics. More research has led me to believe that erring on the side of caution would be to use lower pressure guns. I have multiple other 20 gauges to use modern loads with. This gun is less a target busting, game killing ‘tool’ and more of a shoot occasionally for the nostalgia type gun. I’m trying to get ammo to hunt this fall with it. Anybody reload? I’d not argue about price in the least.

I am currently traveling and will examine the proof marks more closely when I get home. Current in Omaha, NE for the next 10 days, followed by northern Michigan (Traverse City area) for a month.

https://www.clayshooterssupply.com/...mond-shot-fibre-wad-flat-10-boxes-25rds/


Clay Shooters Supply has Gamebore 2 1/2" shells in stock.

What is low pressure? Each person can have a different answer. I spent a lot of time and effort figuring out what was low pressure for me. In 12 gauge it is any load between 5,000-7,000psi at a velocity between 1100-1200fps. Payload can be 1 to 1 1/8 ounce for a lot of flexibility. In 20 gauge I bump it up 7,000-9,000psi for 7/8 ounce loads going 1100-1200 fps. Yes you could decrease both to 3/4 ounce but those use faster powders and often are higher than expected pressures. My gun can handle 7/8 to 1 1/8 ounce shot payloads or will not be shot.

If I am using them for hunting I bump up the shot size for more pellet energy down range rather than boost velocity, payload or pressure. I have killed hundreds of dove with 1/2 ounce to 1 ounce loads all going 1150-1200fps. It is not the loads fault, if I don’t kill a bird, it is mine. Good range distance control and refusing to take poor shots are required but even monster loads are no miracle for shooting. Take a limit of dove with less than a box of .410 shells and you have had a great shooting day.

There you have my two cents. 5,000-7,000 psi for 12 and 7,000-9,000 for 20. Trim hulls to 66-67mm and use in both 2 1/2” & 2 3/4”. Just made my life so much easier.

Mike,

Have you shot these shells?

Thanks
Ken

No but my friend purchased some at the Southern Side by Side event last month and said they were pretty light. Described them as being equivalent to B&P's.

Very well said.

Agree that reloading is best way to obtain low pressure shells, especially with current spotty availability from RST and others. I reload for my 2.5-inch chambered 20 gauge using WSF and Longshot, straight wall hulls (Cheddite, Fiocchi, Rio, Federal), and roll crimp them. Roll crimping, although not as necessary for your 2.75-inch chambered gun, is still a way to get around buying a press. I had some loads tested by Precision reloading last year using the aforementioned powders and both 3/4- and 7/8-ounce loads. I tried to post the results here a few months ago but couldn't manage to manipulate the PDF files into a form which was accessible here. I would be happy to forward the results to your email if you want to PM me with it.