If we are talking about how Native Americans loaded their trade guns, then there have been several references in period journals. "Blanket wadding" is mentioned... Grass is the other one I've seen... or no wadding at all.
In appendix I in S. James Gooding's book "Trade Guns of the Hudson's Bay Company 1670-1970", he includes letters he obtained from company archival records. A letter dated June 6, 1859 addresses the problem of burst barrels. It states...
"These accidents must arise from carelessness, or improper loading. It is stated that in Buffalo hunting the hunters are on horseback and carry the Bullets in their mouth, dropping them down the Barrel in this way and then firing without any wadding. If this is the case, the instant the nose end of the Barrel is depressed towards the ground, and deviated ever so slightly from a parallel line, there would be a Windage between the Powder and Ball, and the most costly Gun would be as liable to burst as a N. W. Gun of the same weight. If grass is used as wadding it would also most likely lead to occasional accidents."
When it refers to "same weight" it refers to the weight of the barrel, not the whole gun. When these letters refer to barrel weight, they are concerned with cost and strength. The thicker the barrel, the stronger it it, the more the barrel weighs, and the more iron it uses to make. Iron was sold by the pound (or ton). They wanted a safe product, and complained to the company leaders (and gunmakers) when customer complaints came in from the field. But they were also concerned with the amount of money they were spending per pound for iron.
I've never seen a period written account of tow being used.
I think this is one area where we can make a compromise to modern safety and not be 100% historically correct.