I read that the Texas Rangers put a layer of pure Lard on the Pickett bullet for the Walker or a layer over it?
Doubtful this was done in combat but maybe was a wistful post-war "assumption"?
I highly doubt it. It may, however, be something true that has increased in error over the years...
See back in the 1970's Civil War reenactors using blanks often tried to use lard or Crisco to seal the faces of the chambers in their revolvers. This was because with only a blank in each cylinder, they often got chamber fires as the sparks would bounce back a little from the forcing cone on the barrel. So I can tell you with first hand knowledge that lard or Crisco in summer heat will liquefy, making a mess of the handgun and holster, and messing up the powder. IF I had been in Texas in the summer heat I'd be amazed that the tub of lard wasn't already liquid when it was opened.
Now, it's a bit different, of course when you jamb a bullet into the chamber, as far as fouling the powder, but the stuff would still be liquefying and running out of the cylinders if you loaded your Walker, then covered over the ball or bullet with lard...and would be gone in very short order if you then holstered that revolver with the muzzle toward the ground.
I think it's more likely that they cut beeswax with lard to make the wax a bit softer, and used that for bullet lube. Beeswax can handle the heat. Over time I suspect the detail that it was a mixture of the two was lost and your source merely said or wrote, "lard". That would be my guess. I've seen a similar situation with folks relating history, who started out with a book on natural dyes in New England which said that yellow wasn't very colorfast, and would fade easily in sunlight. Folks over time then assumed the book applied to all of the East Coast of America, and failed to note the Maryland flag of the time period had a lot of yellow in it. (The error was taking what applied to New England, and then applying it to all 13 colonies)
LD