tool is brand new . having trouble with missfiring the shells have a slight ding in the bottoms

It sounds like the hammer is just barely contacting the power load. Since a .22 if a rimfire cartridge, the hammer must hit it hard on the outside edge of the power load. If you only see a slight mark, you probably are not holding it tight enough to the work both before and during the firing process. If you release a little pressure on the tool as it fires it can effect the firing of the shell and it could cause the fastener not to go in all the way. For the unit to work correctly the power load must be flush and the barrel completely compressed. Also check to see if the barrel is dirty as powder residue will build up on the barrel and need to be cleaned for it to move correctly. Use a solvent meant to clean a gun barrel and you should be all set.