I did get a chance to finally slug the bore on a new 2007 model 38-55 came up with
.379 groove to groove
.376 land to land
I would like to try a .379 cast boolet but I think the .380 will be the better choice I am going to go with he longer starline brass :I just hope it will chamber on .380
20:1 mix flat base bullet
I wonder if any 38-55 shooters out there have problems with the .380 bullet when closing the action

376/379 sounds like some pretty shallow rifling,.0015 deep

I had problems chambering .380 bullets in the H&R Target I used to have. I solved it by running loaded rounds into a resizing die just enough to reduce the diameter at the top 1/8" of the neck.

My H&R is .380 groove diameter and .375 land to land. It will not chamber a .379 bullet unless I size the loaded round like Leo mentioned above.
I have not even tried .380 bullets yet. I probably should use .381 bullets but I know they will not chamber unless I turn the brass or have the chamber opened up.

I keep you posted my buddie who cast say he is going to cast some boolets for me at .3795
which drop out of the mould 20:1 mix.
I am going to try the lee factory taper crimp die also:
I also did here the 2007 model barrel has a tad larger chamber (throat) will see the out come
I think soft lead or BP loads I would like to use .380 which runs around a BHN of 10
I think if I went to a harder cast with a gas chech like BHN of 18 I would stay with the .379