doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Low Pressure Question

To me 5000 PSI is the same regardless of what powder you use...

An SR-7625 load and a 700X load for example both producing equal pressrues are the same regardless of the pressure curve.

I shoot a damascus double. A fellow shooter insisted some powders produce less stress because the pressure is spread out over a longer portion of the barrel.

I think it's hogwash. Opinions please.

Thanks,
CraigF

Progressive powders do spread out the total pressure.

You peaked my interest - I have 7 booked 1.25 lead loads from BPI laying in front of me all with identical components except the powder - pressures range for 7500 psi with 800X to 10,000 psi with Unique and 10,500 with WSF. IMO any two 10,000 psi loads place indentical stress on the firearm. If the pressure curve was significantly differnt the slower powder (providing same components) would show a lower pressure. Just out of curiosity what is your pressure goal for the Damascus barrels? Just my thoughts.

Husky:
Not to be a nudge... but the word is "piqued."

Sorry for the public schools...

Geez, just when you think you know some douchebag, he shows you he can masturbate mentally, too.

That's "too", as in addition to his normal form.

Will the wonders never cease, and, desist?

We can hope, I guess.

Best,
Ted

"Normally" if you use powders having different burn rates with the same amount of shot to the same velocity you will get lower pressure with the slower powder. If you load them to the same pressure you would normally have a higher velocity with the slower powder. Although it will only be a slight amount the slower powder would also shift the point of max pressure a bit down the bbl. "Peak" pressure is normally measured at 1" from the breech to insure the max is always recorded. Even if the shift is only 1/16" the bbl wall is now a bit thinner.
By careful choice of powders you could load 1�oz of shot to 1300 fps & 1oz to 1200fps & have the same identical "Peak" pressure. If you think the heavier load doesn't put more stress on the gun, then you have a total failure to grasp internal ballistics.

"An SR-7625 load and a 700X load for example both producing equal pressrues are the same regardless of the pressure curve."

That's just imbecility.

'Peak' pressure is just that, peak chamber pressure.

The work done is contained under the pressure curve.

That's why there's a curve.

Shotgunjones-

But will it make a difference in a gun proofed for 850BAR?

I keep pressures low, 50% or less of proof pressure 5000-6000 PSI.

A chart showing 4 pressure curves all run with an identical 1�oz load to a 3 dram equivalent velocity has been posted here numerous times. This was run by DuPont back in the 1920's as I recall. Pressure curves are shown out to 10" from breech. Of note is the two points of maximum spread between the curves is first at the peak point inside the chamber, about 1�" from breech. The curves all then cross & switch positions about at the end of the chamber. The 2nd point of max spread between them then occurs at from about 4-6" from breech. Now pressure is considerably lower at this point, "BUT" bbl walls are also considerably thinner here as well.
My personal take on older guns is to restrict the amount of shot used as well as its velocity to just what is actually needed. I then try to use the fastest powder that will keep pressure within a 7K-8K range & figure I am doing the gun the best favor by keeping as much of the pressure as possible within the chamber where its walls are thickest. Also I don't generally have to worry about Cold Weather Squibs this way.

It takes the same energy to accelerate shot weight 'x' to velocity 'y' no matter the peak pressure involved.

It's just fizziks.

The pressure curve tells you where in the barrel the work is done.

The question is, as Miller points out, where would you like your 'stress'?

As far as does it make a difference... that's a question you have to answer for yourself. It's your gun and your eyeballs behind it.

Thanks guys now that makes sense.

An example of hoop pressure. Obviously no obstructions. This does show the importance of wall thickness.


The DuPont chart Miller is referring to:


What the DuPont booklet goes on to say:


Pete

Back to my original post...

The Reloading Bench Burn Rate Chart

28. 700X (IMR)
40. SR-7625 (IMR)

700x is FASTER than SR-7625

This is true.

If you load the two powders to the same chamber pressure, the slower powder will provide more total velocity.

The pressure curve will drop off more slowly with the slower powder, resulting in more total area under the curve.

Thus, the loads aren't "the same". Peak chamber pressure is just one data point on the curve.

I keep a bottle of Unique for cast bullets for years. Will try some for my LP loads.

I've never paid much attention to Burn Rate Charts relying on published recipe data.

Thanks all for setting me straight!!!

Was shooting pitted laminated twist 10ga with 10-12ga chamber reducer yesterday. Used 7625 with 1oz and 800x with 1 1/16oz. Clays with 7/8oz wouldn't seal in the very over bored 12 (poor pattern)I think 7625 and 800x hold pressure longer to seal wad in very over bored 12. Black also holds pressure longer (see chart C above). I use real FF or F with 1 1/8 when hunting. PSI in load data is only one thing to look at. Also if you haven't read Sherman Bell's "Finding Out For Myself" articles in the Double Gun Journal, they are very interesting, concerning shooting damascus and twist barrels.

I've shot damascus barreled SxS's for ten years - have tried to keep my loads under 7000psi. IMHO it doesn't matter what powder is used - 7000psi is 7000psi be it BP or any nitro. My BP load is 70grs of 3F and 1oz of shot - fiber wads. If my gun hasn't blown up in a 130 years, it isn't gonna now with 6 or 7000psi loads. Any American made double of years past was built plenty stout [ not like those skinny British guns ] and should be safe with any pressure curve if it's under 7000psi. Paul

An 850 bar gun has a service pressure standard (NOT proof pressure) of almost 11,000 psi--not far under the SAAMI 12ga service pressure standard of 11,500 psi.

There used to be an old wives' tale that black had a much different pressure curve than smokeless. Yes, different--but not much different. As established by both the Dupont chart above and by the tests Sherman Bell ran and reported on in Double Gun Journal. If a gun is safe at pressure X with black powder, then you're not risking it shooting smokeless loads at the same pressure.

I read that Unique burns in a similar manner as black. I am not sure about using slow burn powders with light shot charges in Damascus barrels. Many old quality guns had their barrels "swamped" in a severe manner. That means they got thin quick! A powder like Red Dot will propel a 1 oz charge below 7000 psi and it will be consumed before the wall thins. 7625 will hold pressure out a foot or so.

bill

Another chart of interest comparing FFFG and 7625


[img:left][/img]

None of these grafts indicate the milliseconds during which the pressure curve takes place



I believe Miller previously observed that the time from ignition of the primer to the wad and shot reaching 12" is so short, it's unlikely any human, or gun, would preceive the difference between BP and fast or slow burning smokeless.

n"None of these 'Grafts' hey, Drew-bie?"" Well, no 'skin off my nose, but your post might have more credence if you had written "Graphs"--But then, as a member of the Medical profession, perhaps you are a plastic surgeon, so the word "Grafts" came to mind- either that, or a Tammany Hall "fixer"-- also Graft is applicable there.

One "Great BIG Ol Humongous" difference in Black & 7625 is;
You could load a 1/2oz of shot over a dram & a half of black & drop it in a 10ga shell & get essentially a .410 load out of it.
Try an equivalent load using 7625 & it wouldn't build enough pressure to Blow your Nose.
It takes a certain amount of heat & pressure to burn Smokeless efficiently & the slower it burns the more it takes to insure adequate burning. Slow powders are made slow by being treated with a "Retardant" so they don't burn so fast.
You keep shooting those slow powders under light loads at low pressures & one day you'll get a squib, "if-fen" your're lucky.
Its not unheard of that an improperly ignited load of powder can produce a "Secondary Explosion" which can take a bbl apart, about like an obstruction.
You've been warned, whether you want to believe it or not is strictly up to You.

Sunday I loaded up 25 rounds (1-1/8 oz. and Unique) before heading out to shoot a few rounds of skeet, was pleasantly suprised how mild they were compared to 1-1/8 Wally World Federals I often shoot in my modern doubles!

Didn't have the correct bushing for 21.0 gn of Unique so I used my Lee scoop & electronic scale. Talk about slow!

For a list of relative burn rates of many powders: go to Google and enter:

Burn Rates Nitro 100

You will see a list of 145 powders starting with the fastest.

Good post 2-piper. You are 100% correct. That's why I don't use 7625 in cold weather. Real black will ignite easier and doesn't need compression like smokeless. If it did, wouldn't be shooting the flinters. I've had squib with other powders in cold weather and try to stay with faster powders or heavier charges when it gets cold.

Craig, I'd guess that the main issue there is velocity. The el cheapo promo loads are often pretty snappy in terms of velocity. It's largely velocity and shot charge that influence recoil, and you need some recoil to make dirty old autoloaders work. Guys with dirty old autoloaders are happy with those Wally World el cheapos, but you can do better in terms of recoil in a fixed breech gun by backing off the velocity. Also the shot charge, assuming you don't need it. I shot skeet this past weekend with a 6 1/4# British double, 7/8 oz loads. Gentle on the gun, gentle on my shoulder, and breaks the heck out of skeet targets.

Here we go

http://www.claytargettesting.com/study2/Study2.3.pdf

Federal 3 dram 1 1/8 oz. Gold Medal

"The primer pressure peaks at about 1/10,000 second; the pressure then drops a bit before climbing again as the powder burns. In this case a peak of about 9000 pounds per square inch (psi) begins to drop at about 7/10 of a millisecond. The shot leaves the (30") barrel at about 3.5 milliseconds after ignition."

The pressure is down to about 500 psi by 2 milliseconds.

"The fanciful pressure curves of shooting magazines and gun-club talk, existing as they do largely in thin air, can take any shape that will buttress an argument. Let�s consider the ubiquitous �sharp jab vs. sustained push� descriptions. Proponents of slow-burning powders describe the benefits of low, extended pressure curves; users of Red Dot� are advised to switch to Green Dot� to enjoy the latter�s more gentle curve.
Let�s see how different these powders really are. Once-fired AA hulls were loaded with amounts of Red Dot and Green Dot to give about 1190 feet per second (fps) as measured by an inductive chronograph.
The following graph compares typical results for each powder.
The Red Dot pressure peak goes about 1500 psi higher than the one for Green Dot but with respect to time they are virtually the same, differing by no more than 1/10,000 of a second and generally far less.
I just don�t believe that anyone could tell the difference when shooting them. The people who experience Red Dot as a jab, Green Dot as a push, must be relying more on their own preconceptions than any differences in the pressure curves produced by the two powders."

PB is also compared.

Gough Thomas reported a "blind" test in which shooters fired ammunition in which the major factors impacting recoil-- shot charge weight and velocity--were the same. Only the type of powder (and the weight of the powder charge) was different. The shooters unanimously selected the shells with the faster burning powder as having less recoil. Maybe explained because the weight of the faster powder was lower than that of the slower powder, and the recoil formula includes ALL of the ejecta (wad and powder, as well as shot)?

Purely intuitively, I switched back to 700X after 7625 experiences, and am staying there.

Two Piper is exactly correct.

Alliant does not list loads under 7,000 psi for just this reason.

My experience with Red Dot is that it's not worth a crap under 8,500 psi. Certainly the current production Red Dot can't be trusted under that. It's at it's best with a 1 1/8oz load, a name brand wad, and a goodly charge. Clean and complete burns then occur.

Promo works better in light loads, at least for me.

Yep, I have also had 7625 squib loads in my 10 ga, so switched to Pb.

Pressure is pressure is pressure. The metal cares only for the thinnest wall between the breech and wad base at the instant of pressure peak. Depending on pressure decay and wall thickness as the wad moves down the barrel, it might well be that the maximum stress would be after pressure peak.

Is Promo powder something other than cheapo Red Dot?

DDA

Promo is a blend according to an Alliant tech via phone call when it was first introduced. Powder that didn't make the cut for canister grade as Red Dot or American Select or Green Dot is blended to the approximate performance of Red Dot without the density consistency. I've had good success with it. The density varies with lot, but then so does modern day Red Dot. I'm currently using a MEC 35 bushing to throw 19.5 grains of Red Dot (the stuff is fluffy) and anything less under 1 oz of shot won't burn completely. This powder is about three years old.

We shoot a winter skeet league here in northern Wisconsin, so we get plenty of opportunity to test loads in cold weather. I've switched to Extra-Lite pushing 7/8 oz shot in my vintage Brit 12. Pressure runs around 7500 psi, very clean-burning, no bloopers at all. Sometimes up to an ounce for some Sporting Clays targets. Powder charge is relatively light, in the 15-16 grain range, depending on the specific load. I'm a big fan.

Drew posted this link:

claytargettesting.com/study2/Study2.3.pdf

Looking at the RedDot/GreenDot pressure curve in the Clay Target article it convinces me that the pressure curve arguement is more academic than practical.

I've been shooting my Birmingham proofed LC Smith for over 15 years (850 BAR proof - 650 BAR service). I used 7625 and the PB early on but started shooting a 7/8oz RedDot load in Federal Paper hulls that list at 4800 PSI @ 1200 FPS. I'm a mild weather shooter so I've never experienced a squib load with it. Paper loads look so appropriate in the old girl and I even sneak a sniff occassionally.
A 1oz 700X load at 5000-7000 PSI (depending on primer) feeds all my SxS's.
In my original post the term "hogwash" might have been a little strong.
Craig AKA nitroproof

Craig, in the specific case of your gun, "hogwash" may not be too strong. Your gun's service pressure is not far off American SAAMI standards with an 850 bar proof. 650 bar service is right around 10,800 psi, so you don't have much to worry about at all with reloads, even building in a reasonable safety cushion.

Note: 650 bar does not come out to 10,800 psi if you use the 14.5x formula to get psi. However, per the Birmingham Proof House, under that system, those were bars as measured with the old lead crusher system. They converted to psi equivalent to get the 10,800 figure.

Mr. Brown-

So if 650 BAR = 10,800 then my gun was proofed at over 14,000 PSI? It still won't get any Wally World Federals!

Craig

Short version until Bro. Larry responds:

650 bar is standard CIP (British and European) service pressure for shells designed for guns proofed at the CIP standard of 850 bar

European (CIP) proof pressure of 850 kg per sq. cm. (BAR) = 13,920 psi proof pressure = 10,730 psi service pressure (SAAMI)

Craig, Drew has the exact service and proof pressure figures. No, I would not feed it standard American factory ammo either. However, you do have more room to work than with some of the older Brit/European guns.

I've always kept my loads [ in damascus or twist barrels ] under 7000psi, usually around 6000psi with no ill effects even in the winter. Is nitro dirty ? Not if you've shot black powder. The only powder that gave me trouble was 4756 and that was in the winter with 7/8oz loads in a 12ga. That was a poor selection. With light 12ga loads [ now 3/4oz ] I've used 700x, Red Dot, Clay Dot, and now Promo. Is the Promo dirtier - yes, but not anything that's too bad. Does velocity differ with low pressure loads - probably, but again not anything that matters. So what if it goes up and down by 6 to 800fps. At ranges out to 35yds what's the difference in leads- 4 or 5 inches. Big deal. At one time I was reloading for myself, wife, daughter, and granddaughter - about 40 boxes per week. Now I'm down to about 20 boxes for the wife and myself. I look for any savings there are and Promo is the cheapest powder and 3/4oz helps a lot. They break clay targets just as well as my old 1 1/8oz loads. Just my 2 cents. Paul

Powder isn't the only culprit. I've found that the CB-4100 12ga wad works quite well until it gets cold, then seems to produce a greater number of bloopers regardless of the powder.

Hi,
just bought a mec to reload 2 1/2 inch shells for an old damascus barrelled gun and wonder if you or nayone would have some recipes for 3/4oz or 7/8 oz to stau under 7000 psi?

any help would be appreciated.

thanks george

I should have mentioned the gun is a westly richards 1905 hammer gun nitro proofed to 3 tons
thanks

You can easily keep them under 5500 lbs. by using 7625 or Nitro 100 (and there are plenty of others) but stick to a fast burning powder. Start with at least one ingredient--hulls and perhaps primers (I would suggest AA's and Win 209s or Chedites). We can help you with the rest of the load.

George, if you are going to roll crimp them, any load that fits into a 2 3/4" folded crimp will work in a 2 1/2" roll crimp.

This is for a 3/4 oz. load. If you roll crimp, Remington hull (nitro, Premier, Gun Club), 16.0 grs. Red Dot, Rem. 209P primer, Claybuster CB0175-12 wad, velocity 1250, psi 6200.

7 /8 oz. load. Same hull, 17.0 grs. Red Dot, Rem. 209P primer, Rem. TGT-12 wad, velocity 1200, psi 6800.

The first recipe is from Clay Buster, the second is from the Alliant Site. There are more from both.

Forgot, you will have to trim the hull to 2 1/2"