375 Win chamber:
http://www.saami.org/PubResources/CC...Winchester.pdf
38-55 chamber:
http://www.saami.org/PubResources/CC...Winchester.pdf
Note the difference in case length, diameter at the mouth, and throating. The H&R barrel looks almost exactly like the drawing for the 38-55, and nothing like the 375 Win drawing.
The 38-55 chamber is designed to be used with soft lead bullets and black powder, and works fine in that capacity. The trouble comes when we try to use smokeless and hard bullets which require the bullets to start out at groove diameter. There really should be a old and modern version of this chamber, and in reality there is since the reamer makers make two different diameter reamers for the same cartridge.
If I wanted to shoot hard grease groove boolits in this rifle I would open up the chamber also. But I don't, I want to shoot it with black powder. It works great that way and I appreciate not having to resize the fired cases beyond a very light kiss with the FL die to reduce the mouth diameter by .002" to get the patched boolit to not fall out when the round is handled.
Tests continue, I was going to shoot it yesterday but the wind was too strong to make it worth it. I am also contemplating getting Accurate to cut me a nicer mould so I don't have to size boolits down so much. I did take some pictures and will get them up here as soon as time allows.