Cooking up a new 20ga load part 2

Before I start, the ultimate plan is to pressure test the loads prior to firing them. I'm a relative newbie, and by no means am I confident in safely making my own recipe.


I found some new, primed Cheddite 2.75" hulls. From BPI I ordered gas seals, fiber wads (1/2"), cork (I think it was 1/8"), and overshot cards. I already have #F (0.22") and #1 (0.30") hard cast lead balls that I made years back. It was WW with a big dose of lino.

I cannot find recipes for these components, so I want to create my own. I have a bunch of Unique, and a bunch of International.

For plastic wads, with unique and a 3/4oz payload, 15gr gives around 9000psi and close to 1200fps. Am I safe in assuming that with 3/4oz, but using a gas seal and fiber, the pressure would still be safely below the pressure limit? Ie, if it's higher, it would still be safe?

Likewise for International, 12.5gr gives around 1200fps and 9600psi with plastic wads. If I work them up with 12.5gr, the fiber wad/gas seal substitution would presumably be below 12000psi?

How do people generally go about pressure testing? It's not cheap, so I think I would prefer to try and make a good guess to begin with, and hopefully verify the guess with data. Would it be smarter to push it a little bit, and try to figure out what's the maximum I could safely do, and then dial it back from there?

My goal is to make a low recoil round mostly for shooting paper and jugs. Maybe a 3/4oz close up coyote load from the 0.22" balls.

I just want to make sure I'd send the tester something that's safe on their end as well. It's concerning, from reading a lot of reloading data, how something like a wad change can add 2000psi. I had no idea it was that touchy! (which is why I have never deviated from a published recipe). Thanks for any ideas. This is my first go at it.

The thing to remember with reloading for shotguns is that there are no progressive signs for increasing pressure until you are over the top. It's your gun, your fingers, and your eyes. I have multiple manuals from powder vendors, component manufacturers, resellers and Lyman that I research before I ever start.
Bill

And just how do you plan to pressure test them? Are you rich?

Follow loading books why experiment?

Buy the equipment to test them but a trigger will still be involved.

IMHO you need to buy a lot of loading manuals and read. You will never get real time info unless it is a printed manual from a company in the business. All the internet unless from a licensed manufacture need to be taken with an open eye and a big dose of salt.

why don't you buy modern plastic cup wads and use the loads in a loading manual (dozens of loads)

Pressure testing isn't that much. Tom Armbrust charges $25 for a 5 shot string. Tom's test gun isn't in danger. You don't have to worry about him. I'm not sure what you are worried about though. You are backing off from published data, correct? You are trying to make a lower recoil load? I'd just load them and shoot them over a chronograph myself. If you are trying for say 1050 fps, then just start low, and work up to that. At that speed, you will never be over pressure with Unique in a 3/4 oz load no matter what you do.