The telescoping gages can be an issue, but usually the problem is with the less than rigid boring setup. If you make a cut, measure it, and then follow it with another cut at the same setting, measure again, make yet another cut at the same setting, and measure again, you will find that the hole keeps getting bigger. They are called "spring cuts" for good reason. The springier the setup, the worse it gets. When you get near your final size, use multiple passes before changing the setting, and check after each pass. Another issue is having a good, sharp cutting tool set up with the proper geometry to make a keen cut, which will have less springing action. For smaller holes, gage pins are my favorite way of checking progress.
I have never seen a snap gage with flat ends. That would be worthless inside a hole. Do not grind them, replace them! Snap gages have their own idiosyncrasies, and a learning curve for getting consistent results. There are plenty of tutorials on the web of how to use them properly, and well worth studying. Practice with a known accurate sized hole until you can consistently measure within a tenth or two. That is not easy, so be proud when you achieve it.
