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A good question. When I had first looked at the MSDS I noted the listing of potassium perchlorate yet I could not find any measurable amount when I took my sample apart in water and evaporated it to look at the various crystal shapes. The shape of the crystals gives an idea of what they are.

After a few weeks I looked at the MSDS from another view versus what I had found in my sample. The main ingredient, sodium dinitrobenzoate sulfonate was not listed as such. Just as a proprietary ingredient. In other words a company secret.
At that time I had just finished up 6 months of communications and raw material samples with a man working in the ATF improvised explosives devices forensic lab. So I contacted him regarding what I had found in the 777. He then obtained a sample and verified my findings through their GS/MS equipment.

I suspected this. Had they developed an entirely new formulation powder they would have had to spend a bundle of bucks on getting it certified through an independent lab. A lot of time and a lot of expense. But if you make a modification to an existing formulation you can generally avoid all of that. So the MSDS info may not be an exact match to what I found to fit into the idea of a slight modification to an existing product formulation.
The patent for Pyrodex had expired several years before this 777 came out. So anybody could have made it on a commercial basis and not been involved in patent infringement litigation.

After working with the 777 for awhile I came to realize that the switch from sodium benzoate to the dinitro version was a logical evolution to cure a few problems seen in 20 years of use of Pyrodex in the field. The switch to the dinitro benzoate eliminated the need for the healthy slug of perchlorate seen in Pyrodex. The chemical texts describe this dinitro benzoate as being highly reactive with charcoal. Which the sodium benzoate is not.

Then there had been field use problems with Pyrodex in that if you did not store it properly it would undergo chemical change. Not a change that would cause it to blow up or blow up a gun. The chemical change would result in erratic ignition properties, erratic muzzle velocities and finally it simply would not work.
There is a previous post that describes this in the poster's gun.

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When this 777 first came out and I took it apart and identified what was in it I had questions on possible pressures. Beyond any question Hodgdon looked at this closely during the experimental batches leading up to the final product.
I noted that in my mule ear .50 cal round ball rifle the 777 came close to the then available Swiss powder. That told me that the 777 produced pressures close to those seen in the Swiss powder. Nothing to get excited about in most ml guns.

The only thing that rattled me was if these "strong" powders are used in one of the Spanish-made in-lines there could be problems. But in our ml guns with the fixed breech plugs I could see no danger.

Hodgdon put a lot of thought into this 777 powder. When I first tested it I remarked that if bp were to become unavailable I would switch flinters over to percussion and shoot the 777 in them. Good velocities even in reduced charges and easy cleanup. But if one gets carried away with the charge sizes one may expect to see some baked on fouling in the bore ahead of where the projectile sat on the charge. Which I saw in some of my Swiss powder testing. If you get powder combustion gas temperatures up close to the melting point of potassium carbonate (in the residue) you will see this fusion and sticking to the bore walls. Then you simply back off a bit on the charge size.

In my mule ear lock GPR the 777 worked almost perfectly. The side lock Trade Rifle was another matter entirely when it came to reliable ignition.

When the in-lines firing plastic saboted pistol bullets started to really sell Pyrodex presented problems in them. I watched this at the gun club one evening when shooting my flinter with Hilljack. Guy and his wife showed up with two brand new Knight "disk" in-line rifles. They came with a box of Pyrodex pellets and a bag of disks holding 209 shotgun primers. Nothing to clean the bore's with. So the guy loads up with two pellets and fires the rifle. Very accurate. Loads and fires a second shot. When he went to load the third plastic sabot it would not seat down on the pellets. He had to pull the breech plug and drive the sabot out the muzzle. So I loaned him some cleaning patches and my bottle of Lehigh lube. He then repreated the two shots with the third stuck.
Now the punch line to this was as he was going through this he was lecturing Hilljack and I on the evils of dirty black powder and unreliable flintlocks. For the whole time! Sounded like a stuck record! The funny part is that he was at the table next to us and his problems cut Hilljack's rate of fire with my .45 caliber flinter.

When I first looked at the 777 and took it apart it was clear to me that they removed most, if not all, of the potassium perchlorate found in Pyrodex to get rid of the little crysals of potassium chloride found after firing it. The problem with the plastic sabots was that as you pushed one down the bore the little crystals would be forced into the surfaces of the sabots to a point where you simply could not push them any further down the bore.
Then compared to Pyrodex they increased the ballistic strength to get velocities up. The in-line crowd expected near smokeless velocities. Without the smokeless pressure surge.

When 777 first came on the market they stated that it was intended for in-line ml rifles. They did not recommend that it be used in sidelock guns. Now we see that evolved to where it is suggested that the breech of a flintlock first be primed with a little black powder and then black powder in the pan. The breech prime of BP working like the little bag of bp in large-caliber artillery loadings as an "intermediate primer".

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