In the firearms industry it seems there is always a “trend” that is accepted as the state of the art for a period of time and then something else will come along and replace it. Right now aluminum bedding blocks seem to be the “trend”. I recently posted our views on the ABB so I won’t get into that today but there is a related trend I think needs to be addressed. “Pillar Bedding” or bedding using aluminum pillars.
First a little history: Many years ago when wood stocks ruled the world there was very few things that would improve the accuracy of a rifle as much as “glass bedding” would. Almost no factory guns came bedded and most shot barely acceptable. Glass bedding usually enhanced the accuracy as well as increased the dependability by limiting the effects of humidity and water which played havoc with point of impact (POI). By using an epoxy based product that was reinforced with some fiberglass, thus the term glass bedding, one could form a much better mating surface between the stock and the receiver. By reducing or eliminating any stresses caused by poorly match surfaces it allowed the rifle to shoot more consistently.
In the benchrest community they found that by torquing both guard screws with a torque wrench they could actually tune the way the gun would shoot. They were constantly checking the toque, between matches and even between groups, and most found that the more they shot the rifle, the more the amount of torque would decrease. They reasoned that the stock must be compressing some due to the pressure and stress associated with shooting. As a result they drilled out the holes around the guard screws to the next larger size (usually from 5/16 to 3/8 or 1/2 inch.) When bedding the action they would allow these larger holes to fill up with bedding material. After removing the screws (of course they waxed them first) they would then drill out the screw hole to 5/16th for some clearance, but that would in effect leave a pillar of 1/16 to 3/16” wall thickness of bedding material. The bedding material was dense and rigid so it made a nice pillar that would keep the stock from compressing under the pressure of 40-60lbs of torque, plus the stress of firing the rifle.
Not long after the pillar bedding process was developed, fiberglass stocks came onto the scene. While benchrest shooters were convinced that pillar bedding had a positive effect on the accuracy of their rifles they assumed that the same process would help to improve accuracy of a fiberglass stocked rifle. The process quickly adapted itself to “glass” stocks.
When Chet Brown and Lee Six first introduced fiberglass stocks to the competitive world in the late ’60’s, they used a process that left the stock with a “foam” core. The stocks were made of fiberglass cloth outer shells with the action area and barrel channels actually molded during the initial process. They would use a low density urethane foam to expand the material from the inside and force it out against the walls of the mold to form the gun stock. As a result between the receiver area and the bottom of the stock (where the guard screws are) there was a foam core. The foam was light weight to keep the weight of the stock within reason and when cured was rigid (unlike polystyrene of foam rubber) but had very little compression strength. In short order it was found that pillars were absolutely required in order to keep from compressing the stock when tightening the guard screws.
As a general rule, the same procedure was used to make the pillars as was used with wood stocks. Simply drill the guard screw holes over size and fill them up with bedding material. The draw back to this technique was that occasionally there would be some excessive shrinkage in the bedding material due to the volume of bedding compound that flowed down around the screws. Though this resulted in a less than perfect job from a cosmetic stand point, it had no adverse effect on the performance of the bedding. When guys like my father and Wally Hart and Fred Sinclair started to take on this type of work for their fellow competitors they felt a need to produce a better looking job and the use of precut aluminum pillars was introduced. More on the technical information on aluminum pillars in Part two.
When Gale McMillan introduced his fiberglass stocks in 1973 they were made in pretty much the same manner as the brown stocks. Urethane foam was a major component and this pillar bedding was a main ingredient in all benchrest stocks he made. Gale only made benchrest stocks for the first two years he was in business. Due to the weight limitations in benchrest, light stocks were a must and the materials used were not nearly as strong as they could have been in a stock weighing much more. Pillar bedding was one way to make up for their lack of strength in the receiver area.
Stay tuned for part two on November 2nd!