John,
I think you'll be happy with your choice. I use the Lee die set up you talked about plus the M expander and suggested in this thread.
Here's the expander die:
http://www.midwayusa.com/viewProduct...tnumber=199295
I found it to be necessary to get the bullet to a good start - otherwise I was messing around trying to hold it in place while bringing the press down. That was what I found, anyway.
Also, I sent my Lyman 4500 back to the factory for some fine tuning and asked them to send me the right top punches for the Lee molds. For the C312-185-1R they sent me Lyman #284 which is perfect. Also, for the Lee C312-155-2R they sent me #413 which is right for that one also. Some of the online charts give different suggested matches which don't work as well.
I like the 185 in the Mosin alot. I use the .314 sizer die to lube and install the gas check - it does not hit the bullet - so it's pretty much shot as cast. I think mine cast at between .312 and .313. The 50/50 works fine. I use C.E. Harris' suggestion of 16 grains of 2400 for 100 yard target shooting and it works well.
I also used the 155 grain and it works good, too. I can't quantify it, but I prefer the 185. I also cast for the 7.62x39 so that's mostly what I use the 155 grain for.
Brass was not easy to track down for anything affordable. Once fired is almost out - it goes fast when posted and not nearly the discount from new that other calibers seem to have.
Enjoy