Yes, measuring the OAL of the cases is not a bad start. It is quick and easy and may identify or eliminate one potential source of the problem.
If that eliminates overlength brass as a problem, try this: take one of the cases which won't chamber easily, and cover it all over with permanent marker ("Sharpie). Let the ink dry, then carefully chamber and extract it it (try not to let it get marked by things like feed rails). You should be able to see whether there's hard contact, and if so where: on the shoulders suggests they've moved forward, for example.
Another quick and simple thing you could try is rolling a case on a flat surface, like a pane of glass, to see whether it is bulged or out of round.
A number of people here have suggested FL sizing, and that is one option, but neck-sizing, properly done, using brass fired in your rifle, should always result in your loads chambering easily. If not there's a problem, either with the brass or the way you are loading it. As I said earlier, I have for years only neck sized, and this is in a range of calibres and for a range of action types, with some brass withstanding many loading cycles with no more than the initial preparation and regular neck annealing.
