Guess I should'a been able to figure that S/L = standard length, since it's so obvious now lol.
But I tell you the Beretta USA site does not give up much for info on specs for each model, RL or not, I cannot find LOP or drop at comb and heel for nuttin' nor do they seem to list any 20 ga target or sporting configurations w/ RL stock.
Bottom of page is LOP, DAC, DAH and other info.....
Don't laugh...LOP is listed the same for SL & RL
No 391 20ga PT in the Beretta listings