Any sort of flat head drift that is smaller or close to the diameter of the pin will do, but using a phillips or pozidriv screwdriver, or in fact any other pointed head tool, will likely damage the pin or at the very least scratch up its surface, since the pins are not likely to be very hard steel; it won't do the screwdriver any favours either, since screwdrivers are not meant to be hit with hammers and mallets (that's one of the places where DIY injuries come from). You should be using the right tool for the job, and that does not have to be expensive. 'Pound shops ' invariably have a few tools in them, they're not normally devastatingly brilliant quality of course, but it is likely they will have punches and flat drifts. Use a small hammer to lightly tap the drift - not a bloody great big lump hammer - as a big hammer will cause damage and transfer shock to other parts of your weapon.