Al,
I don't know if its batch run, but I've used M1 in my 99 truck since new and it has 217,000 miles on it. Still runs great. The new 2008 truck I bought a yr or so ago has had M1 since the first change as well and now has 31,000 with no problems. There's a site called bobtheoilguy.com that has some really knowledgeable folks on there. M1 seems to get a lot of following. I'm sold on it.
But on the double shotguns, anything should work fine. Think about the surface speed and pressures and temps involved...very little of any of those...use anything you like.
