[GP100man]

it`s neccesary to let the case heads go by the recoil shield.On the GP insert a case & ya should have between .008-.012, .010 being optimum between case & recoil shield.

what happens during firing is the firing pin drives the case forward then begins denting the primer , when the primer ignites the primer slips back against the recoil shield (this is why when ya fire a case with just a primer the revolver ties up & won`t rotate) then pressure starts to build from the burning propellant pushin the case back against the recoil shield reseatin the primer, as pressure continues to build it seals the chamber & pushes the bullet on it`s way.

wanted to add: brass is a memory metal , meaning it likes stayin the same size .
during firing the pressure makes it seal in the chambers & after that pressure is removed it releases & tries to go back to it`s original size .
when loaded to over pressures the cyl actually swells & the brass with it & when the cyl returns (hopefully) to it`s original size the brass can`t & thus a stiky situation!!!