Interesting info. I have a 300 PRC in the works. Being build on a Rem 700 Ultra Mag action, and I'm contemplating using a DBM vs the BDL bottom metal. Spoke with a local 'smith who had just completed a 300 PRC based on the Ultra Mag action. Stock was a Manners T4A with M5 DBM inlet. DBM of choice for this build was Accurate Mag CIP LA (3.850). 'Smith said and I looked at the build, that the receiver had not been altered (milled) however the stock inlet had to be lengthened slightly to accommodate the AM bottom metal. Mags fit and and rounds feed flawlessly.
All this leads me to wonder if the Ultra Mag action has anything to do with it, or if the AM bottom metal makes the difference.