Is 80 grit alright to use in lot I give tumbler ?

You could but I wouldn't recommend it. The Lot O Tumbler works a lot like the vibratory tumblers so the coarse grit might work too quickly and harm your barrel. We hear of people doing a coarse step in their rotary tumbler to break the rocks down and smooth them out and then jumping to the Lot O Tumbler. Otherwise it's powerful enough that you could skip the coarse step entirely and start with the medium in the Lot O.