There are a couple of different issues being discussed here, and I would like to add something if I might. I think I have a unique perspective on both.
My guess would be 70% of the stocks we sell never get bedded. To this group I am sure the percentage is much lower be generally long range shooter want to get everything possible out of their rifle when it comes to accuracy. Unless you are buying a custom shop rifle or one that uses the squirt in thermoset bedding production rifles are not bedded. With plastic stocks the recoil lug is molded in, wood stocks they are machined in. In either case we can do as good or better a job of inletting the stocks than the mass producers. So, we say, your rifle should shoot as well or better than it did with the factory stock without bedding it, but, if you want the very best accuracy from your rifle, you need to glass bed it. It may not improve the accuracy much because we find that with most production barreled action and a McMillan stock, you can get very close to the accuracy potential without bedding, but you will never know how much that improvement is going to be until you bed it. A good clue is if your rifle is shooting 1 moa your improvement is likely to be very little. Very few productions rifle will shoot a lot better than that even if the shooter can. Any larger groups than an inch can give you hope that the bedding will make a bigger difference.
Now to the really important part, pillar bedding. I think I can speak to this issue because my father, Gale McMillan was the originator of the practice. It came out of necessity and had nothing to do with accuracy. In the early days of fiberglass stocks, both Brown Precision Stocks (the originator) and McMillan stocks were made using the lightest material we could find. As a result both had a similar problem. Brown used polyurethane foam to blow out the cloth against the mold and because they molded their receiver area and barrel channels in, there was foam under the action. We used a very light filler made of epoxy resin and micro balloons. With both stocks you could crush the material between the receiver and the trigger guard by tightening the guards screws. The more you tightened the more the receiver would move and the more your shots would wander.
To solve this problem my father would drill the guard screw holes out to 3/8". He would wax (Johnson's Paste wax! Still the best mold release on the market when it comes to bedding) the screws up and then let the bedding material fill in the hole around the screws during the bedding process. BTW he used Duro Steel filled Epoxy until they added concrete to the mixture for some unknow reason and it no longer was suitable. In an effort to find a substitute, a friend and customer who own a Marine Supply and Boat store told him about Marine Tex. he was also the first to use Marine Tex for bedding........back to the point, afterr the bedding material set, he would drill the holes out just slightly bigger than the guard screws so the pillars were made of bedding material but they were dense enough to stop the receiver area of the stock from compressing.
Eventually we found aluminum pillars to be easier as just as effective so we switched. Word spreads fast in bench rest community and some everyone was pillar bedding.
Today we refer to it as state of the art. But, technology and materials have changed over the years and all but our EDGE Tech (we actually make them with aluminum pillars)and bench rest stocks (Gale was th first to glue a benchrest action into a rifle and toady a great number of benchrest rifles are still built that way)have a dense enough material in the action area that using normal torque settings on the guard screws the material will not compress at all. The Marines tested the stocks we made for them under 100 ft lbs of torque and the got less than .0001 compression on the receiver area. Of course we built those stocks to be Marine proof, we recommend 45-50 in lbs on the guard screws.
One last thing, pillars do one thing and one thing only, stop compression. They don't increase accuracy or reliability and they don't allow you to remove and replace the barreled action any more often without degradation of the bedding. If a McMillan stock is bedded properly using a good compound, like Marine Tex, pillars are unnecessary. So why do we use them? Because it's state of the art, and that is the way people expect it to be done.
I hope this helps.
