Bore gauge - to borrow, rent or buy
Those are telescoping gages (snap gages). A dial bore gage (like the ones they use in machine shops) have three prongs (tips) to measure the bore at the top, middle and bottom. But the telescoping gages will give you an accurate measurement if you use a good calibrated outside mic to measure the telescoping gage. The telescoping gages will also measure out of round conditions, you just have to have a good feel.
So the telescoping gages (which are not very expensive) will do the job if you have a good outside mic to measure the telescoping gage.
treblig