Here are our (McMillan Fiberglass Stocks') thoughts on the use of Kevlar when making a synthetic gunstock. I first want to say that all of the following information is based on research done using only the molding methods that we use combined with materials and laminating resins developed specifically for our method. Second, I don't have a spell checker on my browser so don't be too tough on me. It'll will take long enough to type this thing without proof reading it a dozen times or so. Third, knowing that competitors of ours do use Kevlar in their stocks I want to make it clear this is not a condemnation of their stocks or processes.
Just to clear the record, we do make some stocks that contain Kevlar. All of the stocks that we make for Remington have some Kevlar in them. When Remington was owned by DuPont (Kevlar is a DuPont fiber)they considered it a good corporate image to include the material in all the stocks they put on Remington rifles wherever possible to do so. When they approached us to make stocks for them and we told them that we didn't use Kevlar they stated "If you want to make stocks for us, you will use Kevlar."
In the mid 1970's we were approached by the Marine Corp to try and develop an M-14 stock that would not break. It seems that their match rifles would from time to time fire out of battery and when they did it had a tendency to destroy the wood stock and take the tips of the shooter's left hand (assuming he's right handed) with it. It had to do with the placement of the hand while in the sling. In any event they wanted the stock to survive the experience and protect the shooter's hand.
Shortly before this time Kevlar had gained some popularity with its use in bullet proof vests and helmets. The Marines sent us some material and said "try this." For those of you who are more technically minded there is an excellent section in the rec.guns faq specifically dealing with Kevlar and its properties. Though none of it deals with Kevlar and how it relates to gunstocks, it is very thorough in its explanation of its qualities.
From the testing that we did and the subsequent usage of Kevlar in Remington stocks we reached the following conclusions:
1. Kevlar was a bear to work with. Hard to cut, impossible to machine. As a result its use was limited to only those places where there is no inletting required. You can't file it so if any happens to get in the seams you were in trouble.
2. It didn't saturate well when used with epoxy laminating resin. The fibers are wound so tight that the cloth never really absorbed the epoxy, at best it was just coated with the resin when "wet".
3. It didn't conform to the mold as well as it needed to. Because the fibers were wound so tightly, they didn't have the pliability needed.
4. Very poor laminate. Since the epoxy never permiated the material it never became unitized when used in multiple layers. You basically had two layers glued together as opposed to one thicker layer as you get with fiberglass.
5. Though Kevlar has a very high longitudinal strength, tensile strength, it lacked stiffness. What makes Kevlar such a great material for a whitewater canoe is that it can flex and bend and conform to the water without breaking. Unfortunately this quality does not make for a good gunstock. Even those who sell Kevlar stocks include graphite in them to get the stiffness necessary to suffice as a gunstock.
6. When Kevlar has been used in a laminating situation and then cured even some of its great strengths are lost. Prior to being wet it would be impossible for even the strongest man to "tear" a piece of Kevlar with his hands. Using one of the stocks we made for Rem. we cut a section of the cured shell that contained Kevlar. It was fairly easy to separate it from the layer of fiberglass that encapsulated it as well as being able to separate the two layers of Kevar used. Once we had a single layer of Kevlar I literally tore the test piece in two as easily as if it had been an old towel.
Our conclusion: In order to use Kevlar we would need to add graphite to compensate for a lack of stiffness. This would require two very expensive materials to make a stock that in actuallity would not be as sound structurally as the one we presently make. We decided that though we may sacrifice some sales to those who are sold on "new technology" with hype and promotion, but we refused to raise the cost and produce an inferior stock, just to sell a few more stocks.
Kelly McMillan
McMillan Fiberglass Stocks, Inc.
http://www.mcmfamily.com