Re: .270Wby Conversion to .270WSM
You can rechamber a 270 wby to a 270 wsm. You would have to set the barrel back since the wby case is longer than the wsm. Due to the fact that the wsm is fatter and bigger around, the wby chamber would then be cut away when cutting for the wsm chamber.
I am not sure of your exact situation, but the Barnes bullets might be the problem. I would first start trying diff. bullets. Banres may not be the most accurate....but accurate enough for hunting. You say that you are getting .5". What is your ideal group sze? We must remember that guns and people have their limitations. The wby can be accurate, it may be other factors. Like, bedding, trigger, the barrel, the action, etc. By rechambering you may not get what you are wanting. What if you rechamber and then it only gives you a .75" group? It is hard to know, but know when to draw the line. I would work with the wby and check the bedding, trigger, action, etc. Don't forget, some rifles shoot better not being free-floated. Some shoot better with some pressure applied to the barrel. After you have eliminated all of the possible reasons why it is not accurate as you want, go from there.
To answer your question, it is possible to rechamber to a wsm and is probably the least expensive option. Other things to look at are: is it a sporter weight barrel or bull barrel? Who is the maker? Is it a factory or custom barrel? I know that this can get in depth.
Hope I have been of help. Good Hunting!