The Skeet's gage is to me very good for the price. It gives you readings that let you know exactly what the bore is from both ends, It will read at least 11 1/2" in and also let you know what your chokes are in each barrel accurately,
I have used the one Brownell's and a few others sell, the one that has the removeable heads from 10 ga. down to 28 ga. This one reads to about 16". A very nice gage but a little pricey for me. Skeet's does the same thing. The one I have has a bakelite tube with an aluminum rod that moves inside it.
It is like Jim said, the 12 ga will not expand big enough for 12 ga. chambers.
