20 Ga Duplex Cold Weather Test

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patternfreak
Posts: 19
Joined: Sun May 02, 2021 6:31 pm

20 Ga Duplex Cold Weather Test

Postby patternfreak » Thu Aug 05, 2021 8:20 am

Hey all, I had my 17/16 oz steel/tss duplex tested in a cold weather scenario and figured I would share the data. It is a bit dismal, but since I store my shells inside between hunts it doesn't worry me too much. They will only be exposed to cold weather for a few hours and I don't ever hunt in temps this cold in NC.

The original testing was done at 80 degrees Fahrenheit and was at 1457 FPS, 11890 PSI.

The cold test was at 0 degrees Fahrenheit in a freezer for a few days and then shot immediately. All of them went boom, but the average was 1254 FPS, 9996 PSI.

This is in a new cheddite 3" hull with a cheddite 209. Sam 1 wad. 203 FPS difference in velocity, 1894 PSI difference in pressure. My next step in the testing of this load is to add a 20 ga OSC over the powder to act as a small gas seal. I don't have enough room in the stack height to fit an actual gas seal. My hopes in doing this is to create a little more chamber pressure and hopefully get it to 1300 FPS at 0 degrees. Like I said, I'm not too worried because my shells stay inside, but I would like to make it as efficient as possible. I've seen a lot of duplex loads around 1290-1300 FPS, makes you wonder how slow they actually are in hunting scenarios!



CRNA2013
Posts: 8
Joined: Sun Sep 06, 2020 5:51 pm

Re: 20 Ga Duplex Cold Weather Test

Postby CRNA2013 » Thu Aug 05, 2021 7:01 pm

What powder did you use?



patternfreak
Posts: 19
Joined: Sun May 02, 2021 6:31 pm

Re: 20 Ga Duplex Cold Weather Test

Postby patternfreak » Fri Aug 06, 2021 10:52 am

Lil gun



continental shooter
Posts: 36
Joined: Mon Aug 19, 2019 5:03 am
Location: Edinburgh

Re: 20 Ga Duplex Cold Weather Test

Postby continental shooter » Sun Aug 08, 2021 8:17 am

hey,

Intriguing test and thanks for sharing.

I knew that cold decrease performances by slowing down the burning rate whilst heat does the opposite by accelerating it. It was the 'old fellows' big challenge when, back in the days, they only had once choice of powder and had to adjust from temperatures ranging from -15 C to +45 C and humidity going from swamp like to desert like :lol:

Not sure about SAM1 (though I would think so) but B&P and Gualandi wad have an inbuilt gas seal at the base already; it's devised so that it expand and create a seals upon receiving the first gas increment; adding an extra layer will negatively affect that and the OSC (cardboard i think) will not be a great seal either. It will also raise the sack height which, in itself does reduce pressure too so, could be counter productive. But for the sake of testing ... why not :D

Alternatively, base on my lead studies, there are a few more things which you could also try in order to restore your original performance without having to change the load:

1- close (Spin, Fold, roll) lower,
- your standard rolled crimp should be 2.800" (71.12 mm); try rolling at 69.1 mm - 70 mm
- your standard rolled crimp should be 2.695" (68.45 mm); try folding at 66.5 mm - 67 mm
considering every 0.5 cm will give you around 1000 PSI increase in pressure these should all return the data to tested pressure/speed; obvs, start with the higher closure and work your way down. ;)

2 - use a hot primer: you're already using a Cheddite CX2000 (or .209 as it's sold) but you could use the hotter Federal or Winchester. They are usually slightly hotter in their normal version but I think you have an even hotter version of each.

It'd be interesting to see the results of that as these are all established and tested ways to improve the loads from mid to cold weather but they all work for lead; non-toxic uses a whole different range of materials and might not be entirely the same; although, I would think it'll work to a certain extent

Cheers



patternfreak
Posts: 19
Joined: Sun May 02, 2021 6:31 pm

Re: 20 Ga Duplex Cold Weather Test

Postby patternfreak » Mon Aug 09, 2021 7:54 am

I could definitely use a federal 209a and get the pressure up, but I want to be able to shoot the load in warm weather as well. I plan to hunt in Texas for early teal with a 4/9.5 blend and then hunt the first split of our duck season back home in NC with the same blend for wood ducks. Both of these scenarios will be in 70-85 degree weather. If I added a federal 209 in these situations I'm sure the load would be over pressure. Also, I don't want to have to derprime/reprime 1000 new hulls.

The overshot card is more insurance to me above the powder as well. Lil gun seems to be fine grained enough to find all the little gaps. The sam1 wad fits pretty good in the cheddite hull, but powder could definitely get past it if the shell is stored brass up. I like to put shells in the shell belt of my waders which means gravity will want to pull the powder past the wad. If I have an overshot card sealing the powder off, migration won't be a concern.



continental shooter
Posts: 36
Joined: Mon Aug 19, 2019 5:03 am
Location: Edinburgh

Re: 20 Ga Duplex Cold Weather Test

Postby continental shooter » Tue Aug 10, 2021 12:33 pm

Yeah, deffo agree on the overpressure in warm weather with hotter prime.

Be interesting to see what the difference in pressure is between the shells with over powder card and without. EU literature is all against it, and so are manufacturers (in my academical years I did some placements in some manufacturers); the reason seem to be the incorrect expansion of the wad base -thus poorer gas retention- as opposed to powder migration.

It's similar to the overshot card before fold crimp, said to disrupt patterns.

As soon as I can get out want to run some Patten test and see how much difference, if any, does this make.

Thanks again,

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