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

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.