How should I anchor a hand railing to sandstone steps?
Normally this is done by drilling an oversized hole, filling it with mortar and inserting a threaded anchor. The modern way to do things is to use what is called a "drop in anchor". This is an expanding anchor, kind of like a dry wall anchor. You drill the hole to size, drop in the anchor (tap it in with a hammer actually). When the bolt is screwed in, the anchor expands locking the bolt in place (hopefully). The fit needs to be snug. The mortar solutions will be a lot stronger, but more time consuming because you have to mix mortar and wait for it to set.

One of the problems with using a mortar anchor is simply finding one that matches your bolt. You can use a lag shield anchor as one way around this. Another tricky trick is to use nuts. Thread a whole bunch of nuts onto the screws until you have a solid column of nuts. Make sure the nut at the bottom has a little extra space, even glue an extra nut for extra space. Pour the mortar and then put the whole assembly, railing, bolts, nuts and all in place. Finally tighten the bolts.