doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Pressure vs. Velocity

Thanks guys. I think I will start with factory loads and see what I like as far as pressures, velocities and shot charges. Then I will look at matching what I think works for me, trying a number of different loads. I will follow all recipes exactly. I used to reload a fair amount when I was shooting ATA tournaments and have all the equipment needed.

OK guys - Now my interest is peaked after looking at reloading data. I see that pressure and velocity do not go hand in hand. I am looking at Hodgdon's site and am looking at 12 g, 1 oz loading data. I see many loads that generated a velocity of 1100 fps but the pressure varies from 4500 to 6200 psi. Is there any reason other than cost or availability of components that I would want to shoot the higher pressure loads? I can't see where pressure offers any benefit if the velocity is the same. Is a 1700 psi differential significant?

Tom,
I see you are from WI. The first thing that comes to mind is that with very low pressure and cold temps, you can get poor ignition and bloopers. I'm in Texas and have never experienced this but have read about it a number of times on this board. Second item would be patterning the load to see what is best in your gun. Third would be how dirty the powder is. But 6200psi is a great number. My go to 12ga load is 6400psi by the book.

Hopefully some of the northern folks will be by shortly and give you some powder/load info that they have found works in cold weather.

Hope this helps.
Ithaca1

Tom, in the pressure ranges you're looking at the 1700' pressure difference is totally meaningless.

Hi all, just my 2c worth here. Ithaca is right about swapping components, but and there is always a but, you can if the manufacturer gives the green light. Just as an example, one of my loads calls for Fed 209 primers, but they are discontinued, but Win 209's can be used instead per the powder companies okay. So, to be safe always check and double check.

One thing to save you pulling your hair out, is kind of watch what you post on some of the other forums. Whenever you ask about LP loads, your going to get....."Why? You don't need low pressure, high pressure is your friend" and so on. And for some of the guys, no matter how much you explain, it just doesn't matter. Better to stick here with folks who understand vintage guns. You'll have more than enough good advise on reloading.

As to cold weather loads, I've had good success with 800-X powder, meters like crap, but performs well in cold weather. I keep my pressure around 7000psi and a MV of around 1200fps. And yes I do shoot 2 3/4" reloads in my short chambered guns.

Good Luck!

Greg

If you're willing to explain why 7,000 psi is better than 9,000 psi, I'm willing to learn.

Hey Mike, well when your gun is proofed at 8938psi and you shoot 2 3/4" in a 2 1/2" chamber, then yes, 7000 is better than 9000

I should have stated that I was speaking of vintage Brit guns.

Sorry for any confusion.

Best,

Greg

Alliant 12g Reloading Guide
http://www.alliantpowder.com/reloaders/RecipeList.aspx?gauge=12&gtypeid=3

1 1/8 oz. at 1200 fps in Winchester AA case, Win 209 primer & WAA wad
Unique 21 gr = 9,100
Green Dot 19.5 gr = 9,300 psi
e3 17 gr = 10,450 psi
Red Dot 18 gr = 10,400 psi

1 1/8 oz. at 1145 fps in Winchester AA case, Win 209 primer & WAA wad
Green Dot 18 gr = 8,500 psi
Clay Dot 17.3 gr = 8,740 psi
e3 16 gr = 9,625 psi
Red Dot 17 gr = 10,000 psi

1 oz. at 1145 fps in Winchester AA case, Win 209 primer & WAASL wad
Green Dot 18.5 gr =7,600 psi
Red Dot 16.5 gr = 8,000 psi
e3 15 gr = 8,635 psi

I don't understand the higher grains of Green Dot in the 1 oz. 1145 fps load but checked several times to confirm

Note the Green Dot pressure is the lowest of all the powders listed in these loads. Probably with only an ounce of shot at the lower velocity of 1145 fps it is simply not burning quite as efficiently as in the slightly heavier loads.

There's the answer right there--except I'll make one friendly amendment if you'll permit, Greg: I'm pretty sure that 8938 psi number is service pressure and not proof pressure.

But a reloading recipe that lists 7,000 psi can, all of a sudden, get awfully close to 9,000 psi if it's a 2 3/4" hull used in a gun with short chambers (which, per Sherman Bell's tests, can potentially add an additional 1,000 psi + to the pressure reading). Then add in a bit more in case your powder drop is a couple tenths of a grain higher than average.

I don't see any need to seek out the ultra-low pressure stuff. Under 6,000 psi, for example. But if you're reloading 2 3/4" hulls for short chambered guns, you do want to build in a significant safety cushion. Somewhere around 2,000 psi should be sufficient. Nothing wrong with more than that, but it's not really necessary in terms of safety.