Back in the late-80's, we used urethane foam as the core blank for the aforementioned propeller blades. It was cast oversized, and machined to final dimensions, which were pretty tight. Sorry, can't supply an actual tolerance number.
Basically, the foam core, was cast onto an aluminum blade root/stub. The stub component was less than 12" long, and provided a flange for the blade bearings (constant speed aircraft propellers rotate around their primary axis). The layup proceeded over the foam core and extended onto the aluminum stub. Then the whole setup went into the heated steel mold, which was in a giant press (over 10 ton), for final cure. After the cure cycle, the blade was pulled for initial cleanup around the parting lines. Next, pre-preg kevlar fiber was filament wound around the blade root, where the layup extended over the stub. This became a retention ring, to prevent the structural layup from being pulled away from the aluminum root under flight stress.
The foam core really wasn't structural, although it had to be made to a very particular size. The idea being that the combination of core and layup would overfill the cavity by some specified percentage, yielding proper compression to the fiber layers during the cure cycle. Too big, and finished part would be resin starved, and weaker. Too small, and there would be voids between fabric layers, which is and even bigger structural issue. A bladder, if you can get it in place, is more straight forward, but in some situations, unworkable.
Foam cores can also let you do some other interesting things. For example, on propellers/airfoils, you can split it down the middle, insert, or layup, a supporting spar in the split, put them back together, and wrap with your overlayers. Of course, the more complex the layup schedule, the more chance for things to go wrong.
About the best publicly info you will find on structural composite construction is from the home building aviation community. The Experimental Aircraft Association is the keeper of the flame on that front. However, they don't deal much with closed mold stuff. They have invented other interesting techniques though. Seem to remember that the main spar or boom for one of the early, record breaking, human powered aircraft was filament wound over a section of aluminum irrigation pipe. After cure, the unneeded mandrel was dissolved away with acid.
Most places that are good at this kind of thing don't make their techniques public.