Anyone measure their Head Chamber Volume?

I'm going through the process of checking and measuring everything on a couple new VG33E's I'm building and I ran into a discrepancy with the chamber volume on my 0w0 heads. I had actually calculated the chamber volume to be 53.5cc's based on all the other dimensions of the combustion chamber and the published compression ratio. Everything seemed to check out. Then, I decided to actually measure the chambers using a lexan plastic plate bolted to the bottom side of the head. I measured about 49cc's. I measured two sets of heads and repeated my measurements to be sure I wasn't making a mistake measuring. Same repeatable volume of 49cc's (+- 0.5cc).

I have had both sets of head milled by a machine shop, but they don't take off enough to adjust the volume by more than 1.2cc's (based on removing 0.010" of material - which is more than I would have wanted already). The other set I had milled, they removed 0.005". However, there was some confusion on the second set of heads (as to how much they really removed) and I think it may also have been 0.010". Both sets of heads measured 49cc's in each chamber after milling, so it's possible they did remove .010", since both sets measure the same. I measured the area of the chamber opening at the surface of the head too, and removing .010" calculates to about 1.2cc.

Has anyone measured their head chamber volumes? I would love to know the volume of the chamber is before they are ever milled. If they are around 50-51 cc's, that would make sense.

Since I can't find any published info on the chamber volume of these heads, I wonder what it really is.