In order to determine choke you must know the bore diameter to get an accurate measure. Especially in the earlier 16g auges that had a .650 bore, later ones till the end had .662 bores, so you can see there is a .012 difference.
The brass bore gages you see having a conical stepped shape are only good for seeing that the barrels were not cut, nothing else. Example I was selling a 16 gauge that the barrels were cut to 24 3/16", original length was 26"(Records) the constriction in both was .014. A fellow was interested, and I told him what I just mentioned, he took out his bore gage and said it was reading full/full. So do your research, most all hammerless L.C. Smiths's were between .726-729, and I have measured a few of my hammer guns that were .724. A Skeet's gage is a good way to let you know what constricion you have after getting a bore reading.