SPG is touted as the best lube fer the Holy Black. First time ever a black powder cartridge rifle match was shot and won with the operator not cleaning the bore after every shot was Steve Garbe using his new secrete recipie lube named SPG lube.
It was described as edible and described as a conditioner for the bore like seasoning an old cast iron frying pan. The more you used it the cleaner the bore stayed suposedly. The other lubes ,the yellow stuff in tubes, sold commercially all seemed to be using the "secrete" ingredient that made SPG Lube so good.
I was told a good while back by a guy somewhere around the net that his Buddy in a labe isolated the incredients in SPG and concluded that it contained "mineral oil" as the lube part and beeswax as the medium in which to hold the lube stuff in suspension in a firmer base.
The "yellow stuff" sold was tested and sold by Thompson Center and touted as being tested with a rifle fired 1,000 times and still was not too fouled to load and fire.
Anywhooooo........there are good lubes out there that compete with SPG Lube. I don't know if they season the bore like SPG has been described to do. Season the bore by firing and cleaning with water and "never solvents or oil to ruin the seasoning and using thelube as a rust preventative".
My experience seems to dictate that nothing I've found works to make a bore impervious to black powder fouling except......when the lube is not petroleum based and is natural like olive oil,Crisco,tallow,Canola oil and is in the wax in large enough a percentage compared to the wax......the softer the lube is because of the lube part of the recipe the better it combates fouling and ...goes down the bore in front of the powder(as in the case of a cap&ball revolver having the lube under the ball on the powder and not over the ball but can be under the ball and over the ball also).
You can get into problems with a softer lube on hot summer days or by storing the cartridges in a hot area so in warm weather a stiffer(more wax) lube is a good idea.
Any lube stuff that's natural and in an adequate amount works well when the lube/wax goes down the bore before the powder blast.
In a cap&ball revolver that's needed advise because of the old wifes tale that lube over the balls keeps fouling soft. The rifles with patched balls or anything with a lubed bullet can't help but to go down the bore in front of the powder.
Anywhooooo....most every top competitor in Black Powder Cartridge competition uses SPG Lube. Most but not all.
Probably the shooters using those bullets with the canaverous lube grooves make out the best when fighting black powder fouling.
Anywhooooo...I can use lube pills(grease cookies) over the powder in cap&baller revolvers and shoot all day without much fouling problem. A hundred balls and up to 200 balls fired. After awhile ,even using the lube pills, the base pin in front of the cylinder can use a little solvent or water to stop any drag that begins to happen. I've tried all manner of lubes from olive oil to tallow and Crisco and oils for cooking and....as long as there's enough of the lube type stuff in the wax/lube recipie it works well.....including SPG Lube.
SPG does work well and does it with black powder or smokeless.
I make my own lube with beeswax,parafin wax and tallow and adjust the amount of wax according to the weather being hot or cold. Make my own lube to be more economical.