The below is a cut and paste. It may be a little too much and require multiple reads but I believe good info. Hope that helps.
Black powder and all the subs except Blackhorn are low explosives which burn at a constant fixed rate. Blackhorn is a progressive burning powder, that means the higher the pressure the faster it burns. 777 is the fastest burning sub available at this time and if you do not have to fight curd-ring it is an excellent powder especially for light loads or light bullets but it also works quite well with heavy lead bullets and loads in the 60 to 90 grain area. Because Blackhorn is progressive burning it works best with heavy loads and heavy bullets for instance with a 250 grain bullet in a 50 caliber if you load 777 to 120 grains and Blackhorn to 135 grains you will get very close to the same pressure reading but the velocity and recoil will be quite different. But if you load 120 grains in both the velocity will be very similar but the pressure reading s will show Blackhorn with a much lower longer pressure peak.
I had the pressure trace charts but lost them when my hard drive went out. Here is a bit of info you can look over.
First we will look at the black powders.
Goex prior to late 2000 was more corrosive than the other brands on the market at that time. This was due to the grade of potassium nitrate they were using. Their long-time supplier folded in 2000 so they had to switch to potassium nitrate produced in Chile. Their long-time supplier had been shipping them a fertilizer grade of potassium nitrate while telling them it was a technical grade. They refused to listen to me when I told them that back in 1984. But at the same time they had no choice. There was no other U.S. producer of potassium nitrate they could buy from.
Then in 2001 they got their charcoal problem in hand. After they closed the Moosic plant their long-time charcoal supplier was pulling a fast one on them.
But as it stands now the major brands of BP, GOEX, Schuetzen and Swiss all use a grade of potassium nitrate where the chlorides are measured in parts per million.
On to the subs.
APP, Shockey's Gold, Pinnacle and Black Mag are based on ascorbic acid and potassium nitrate. Only Black Mag's patent shows the addition of potassium perchlorate. Which makes its residue more corrosive than the other 3. APP, Shockey's Gold and Pinnacle are all made by the same company. So there is really nothing that makes one really superior compared to the others.
Blackhorn 209 was handed to me. The mfg. claimed it was not a smokeless (nitrocellulose) powder. So I had at it in the kitchen with different solvents. Turned out TO BE a nitrocellulose powder with 17 parts of an unidentified chemical used to tone it down in the gun. The unknown chemical is highly soluble in water. I just saw no need to spend another day or two in the kitchen to identify it. And given the price per pound I figured it simply was out of the picture. After reading a post or two in this thread I might just take another look at the 17 parts of the unidentified water-soluble chemical and see if that would cause corrosion.
With Hodgdon we have Pyrodex and Triple Seven. The whole patented concept in Pyrodex was the use of sodium benzoate with potassium nitrate. But to get the two to react fast enough to make it a usefull firearm propellant they had to heave in something like 17 parts of potassium perchlorate. When the powder burns the potassium perchlorate simply gives up its oxygen and remains as potassium chloride. ANY chloride will be most corrosive in the gun. Does John Boy use Alantic Ocean water to clean his guns after a shoot?? I think not.
Onto 777.
The patent on Pyrodex ran out a few years back. Then the in-line ML hunting crowd wanted faster powders. A big push came when the plastic sabots came into use in the in-line ML rifles. That 17 parts of potassium perchlorate that was converted to potassium chloride causes a lot of grief with tight fitting sabots. The little crystals of potassium chloride are scattered to the bore. When you would push a sabot down the bore the crystals would embed in the plastic. So you would reach a point where you could not get the sabot down onto the powder charge.
So what we see in 777 is a change to sodium dintitrobenzoate sulonate. Think of it as going up a notch in benzoates. This dinitrobenzoate is HIGHLY reactive with charcoal. So there is no need to heave in a bunch of potassium perchlorate to "strengthen" the powder. This makes 777 a lot LESS corrosive compared to Pyrodex. When I checked the 777 on brass plates there was no surface pitting of the brass as with Pyrodex. Hodgdon's MSDS for 777 shows potassium perchlorate. From what I saw in my steel plate and brass sheet corrosion tests I don't think it has any perchlorate in it.
With this development of 777 Hodgdon can claim that it is an improved version of Pyrodex. Makes getting it onto the market a lot cheaper than going through it as if it is an entirely new explosive composition.
The thing about potassium chloride corrosion in gun bores is that a lot of times the average shooter would never know it is happening. You can get a lot of micro-pitting of the bore which gives the surface of the metal a frosted look. This comes up to bite the shooter if the shooter switches to black powder. BP fouling will then act as if it is welded to the bore walls. Simply because the metal's surface is so rough and pitted.
Just keep in mind that ALL of these powders are based on potassium nitrate as a source of oxygen for powder combustion. As a result they produce potassium carbonate as a product of combustion. This "potash" is in itself slightly corrosive in the bore. Anything in the bore that will dissolve in water to form an electrolyte solution will be corrosive. So this gives all of these powders what might be called a baseline corrosiveness. Any chlorides present will enhance/increase this base level of corrosiveness. Potash itself will only cause a uniform shallow rusting of the surface metal. As soon as you add chlorides you can get pit corrosion that bites deep into the surface of the metal. be it steel gun barrels or fired brass cases.
This is a quote from a fellow named Lou Gram who posted it on an other forum to answer some questions after he checked it out chemically.
