The "L" frames are the 586 and 686's. they are a little beefier then the 66's and 19's. supposed to handles more 357 mag rounds.
Now they did make a "N" frame (large ) 357 the 27 and 627.
And they also make the model 60 ,which is a "J " frame in 357 mag . but they were recently. the little frames shouldnt be used to shoot alot of mags.
Ruger i'm not sure about an I frame . i would be lying if i said anything about it existing or not .cause i don't know.
I have a 19 just like yours paulyseggs the 19 is just carbon steel blued or nickel. nice gun for home protection or carry.

SOUTH ARKANSAS REBEL