I would think snap weights would be better than adding lead core over your mono. I would assume your reels are full and calibrated to be accurate with the depth counter. So adding lead core over this would make that not accurate. Not sure you would even have enough space in your reel to add enough lead to make this even possable. Normally the reels are almost full to get the counter to be correct.

I took your question as you wanted to add the lead over your already in place mono to be able to get the lure down and extra 20ft. Or do you just want to use some mono as a backer so you don't have to put so much lead on. I have personally never used lead, I don't even know how much you need to get to 50ft. I think I heard once that color ( about 10 yards) was worth close to 7ft, so you would need color to even get to 50, then say at least 1 or 2 more to not be having the joiner knot taking the full pressure of fighting the fish. So 9 or 10 color...300yards.....900ft.

We run braid with 1000ft by the reel of 25lb mono backer and 400-50ft by the reel or braid, 30lb. Seems like we get our in calibration in that window, we start checking it at the 400 mark. For us it gets us within about 5 actual feet of distance when measured at 100ft, so from there it's just adjust the fill to get it the measure out correctly. An extra 100 ft by the reel tends to make about 5 ft measured out. But mono is thin, we use 30 series okuma. I don't know how much reel you need to fit 10 colors of lead on, I would imagine it pretty thick and will take up a good deal of space on a reel.

But I am sure someone who runs it will chime in and let you a define answer. But as I'm typing and thinking if you know 7 or 8 color will hit you about 50 ft, I guess the line counter now won't matter at all, cause the depth per color is a known factor. From there any reel you can fit it on should work....I guess what is need to know is how far does each color get you down then just let out and do the math no counter needed.

Now you got me wondering. Lol