What they are probably talking about is your Model 21, Parker, LC Smith type guns. I use the same loads in my Model 21 as I do in my Ljutic without batting an eye. 1 1/4 oz.- 17 gr of Titewad- around 1150 fps and about 10-10,500 PSI depending on which wad I use. Usually a figure 8. But a lot of your older guns like damascus can't take these high pressures..... The disclaimer is because they can't be responsible, even with their low pressures, that someone's damascus or a thin walled gun is going to hold up. The shells are made for a gun that needs to have low pressures, but they can't guarantee a gun that they have never seen or inspected. Even if they did, who's to say a barrel obstruction won't occur? It keeps them out of a lawsuit. At least, that is the way I take it.
