I have never really tried it. It take a lot of practice and even a very experienced sexer can be wrong. Some chicks can be tricky. That is why hatcheries that use the vent sexing method will only guarantee about 90% accuracy.
Remember, you can't do this on any bantam breeds....the hatcheries don't even to it. I guess it is because they are so small. Take your time and be as gentle as possible. Start by pulling gently down at the bottom of the vent then use your other fingers to roll the rest of the vent open. I use the tail bone as an anchor sometime, something to gently push against. Good luck and be careful. This should be done very early after the chicks hatch. This little guy was still wet.
It is best to do it w/in the first 24 hours. Earlier is best. When the chick is first hatched the vent is very soft and pliable. It stiffens up the older the chick gets. As you can see from the pic, this chick was still a bit wet. I find w/ the chick being wet it is easier to grip. If the feathers are soft, wet your fingers slightly so you are able to get some traction.
Feather sexing is all we use. We sex ours after they have fully dried off. Within the first 24 hours is the easiest.
There are 18 different shapes to look for when vent sexing. There are actually 4 that are almost identical. 2 on females and 2 on males. It takes a very trained eye to be correct. We can sex just about anything. My wife is getting where she can sex silkies. Those are very hard since they have more of a fur than a feather. Even in last years issue of Backyard Poultry, it said the same thing I am saying. The following is from the July/August issue: