If the CST action could be summed up in one word, it would be innovative. When really taking the time to think about the history of the bolt action design, you’re not likely to find a great deal of difference from models available today versus models Paul Mauser introduced over a century ago. What sets our action apart?
Competitive shooters get a lot of credit for advancements in rifle accuracy. Any one of the shooters at the top of their game will tell you how important a geometrically correct action is to obtain consistent accuracy. More specifically, the bolt must be in line and true to the center of the barrel’s bore with surfaces of the locking lugs seated square and equal, placing the critical bolt face perfectly perpendicular to the barrel’s bore as possible. To achieve this goal, accuracy minded shooters have sought tight tolerances of the bolt body diameter to the receiver body inside-diameter while lapping lug seats square. “Blueprinting” an action is a common term and is the thrust of this concept. However, a one-to-one fit of the bolt to the receiver would be a recipe for a seized up gun and any “tight fit” is subject to eventual wear. Some clearance must be available to allow the rifle to function without binding, making absolute concentricity in conventional designed bolt guns impossible.
Bolt Harmonic Vibrations
Several rifle accuracy theorists suggest perfect timing of vibrations at the exact moment the bullet exits the muzzle will deliver top accuracy for any given rifle. This is what is occurring when shooters “tune” their rifle by using different components and powder charges during handloading. Adjustable muzzle tuners are another example of this phenomenon. Some rifles require a lot of time and effort, not to mention new barrels, to defeat accuracy-robbing vibrations. What causes these vibrations? A lot goes on inside a barrel during firing, but what about mechanical movement from the action itself? A simple example of this would be to dry-fire conventional actions and feel for any bolt movement. You will detect quite a bit of play allowed once pressure from the firing pin spring has been released. Imagine all that stored up energy on the bolt allowed to release just at the moment of firing and it is easy to see how mechanical “banging around” can occur inside the receiver every time the trigger is squeezed.
Solution: CONE-LOKtm BOLT
We address both of these problems with a better bolt design. If you can imagine holding a funnel and dropping a ball inside too large to slip through the spout, you can visualize how the CST Cone-Lok bolt design works. The ball finds perfect center of the spout every time. The conical surfaces of the locking lugs seated into the mating conical surfaces of the receiver will allow the bolt to self-center every time the bolt is closed. But this is only part of the solution as tapered locking lugs can be found on other actions as well. The innovation behind the Cone-Lok design is incorporating the same geometric interaction at the rear of the bolt as well as the front. A spring pressurized floating bolt handle with a conical face mates into its own conical seat at the rear of the receiver body. The two opposing conical seats forces both the front and the rear of the bolt under pressure to align concentric to center of bore, regardless of bolt fit or wear. Furthermore, since the floating bolt handle is held under pressure from a disk-spring housed in the bolt shroud, the bolt stays locked up concentric and remains static throughout sear release and firing pin movement. The key is a bolt held in place that maintains all locking lug contact in their respected seats throughout firing pin movement, thus preventing any accuracy robbing vibrations.
Angled-Sear Engagement Induced Bolt Lift
Sear override trigger systems are commonly seen on a lot of bolt-action rifles today, particularly American made models. Their simplicity has made them a popular choice with a huge assortment of aftermarket versions available. Unwittingly however, they create a defect when attempting to lock the bolt up concentric and with the lugs equally seated. The angled face of the sear interacts much like a ramp to the cocking piece face. Under pressure from the firing pin spring, the cocking piece will ride up the angled sear face causing the rear of the bolt to rise and the top locking lugs at the front of the bolt to move slightly forward, disengaging contact with their respected seats. All this creates misalignment of the bolt and the bolt face to center of bore, unequal lug seat pressure, and more mechanical movement of the bolt when the energy stored up by the firing pin spring is released. The importance in preventing these conditions has already been explained above. Again, bolt clearance is necessary for proper function, thus making it impossible to prevent rear bolt lift in its entirety. Although triggers with square or vertical sear engagements may prevent the ramping effect of an angled surface, spring pressure at the bottom of the bolt will create unequal pressure of the locking lugs in their respected lug seats.
Solution: Zero-Lift Cocking Piece
The solution to this design flaw was directed straight to the source. The Zero-Lift Cocking Piece utilizes a T-shape design with precision machined flanges extending from both sides. These flanges ride in a T-slot machined in the tang area of the receiver. Clearance from the top face of these flanges and the bottom face of the T-slot is held within .001”. This tight tolerance interaction during closing the bolt into firing position prevents any rear bolt lift caused by an angled sear engagement, yet allows complete free fall of the firing pin assembly during firing. This cocking piece design coupled with the Cone-Lok system eliminates any bolt misalignment issues even with the use of popular sear-override style triggers readily available today. This can be proven by using a depth-micrometer and measuring the depth from the receiver face to the bolt face, taking readings with the bolt cocked and un-cocked all along the bolt face surface, especially at 12 and 6 o’clock positions. The CST action will show the exact same reading all along the bolt face cocked or un-cocked, something you will not find in other actions, not even the best match grade actions available today.
Firing Pin Alignment or Breakage
It has been suggested that a smaller firing pin tip can yield better ignition while minimizing spring pressure. Reducing spring pressure in the firing pin assembly allows easier bolt lift and creates less mechanical energy to be held in check, (vibrations). Perfect tolerances of the common single-piece firing pin inside the bolt body can be difficult and costly to machine. Even then, the problem with angled-sear induced bolt lift explained above could flex or bind firing pins during bolt lock-up and cause the smaller diameter tips to break.
Solution: Magnetic Floating Firing Pin Tip
A floating firing pin tip means just that; the tip is not connected to the rest of the firing pin assembly and can easily travel forward totally independent of whatever is going on behind it. Simply put, it is never put in a bind. This allows the use of a .062” diameter tip with a total free fall to the primer. In addition, the tip can be easily replaced with a new one simply dropped in. Why magnetic you ask? Remember those metal-to-metal harmonic vibrations? Not only does a small rare-earth magnet embedded in the rear face of the firing pin tip prevent loss and allows easy removal and reinsertion, it also maintains contact to the firing pin assembly behind it, preventing metal-to-metal impact before primer ignition.
Action Screw Support
Most of us will agree to the benefits of a floating barrel. But have you ever thought how two quarter-inch screws with about .175” thread engagement each are totally inadequate in supporting all the weight of a floating barrel, especially the much preferred bull barrels? This is a direct carry over from Mauser’s original design, which was never meant to support the entire barrel weight. Placing two small screws at dead 6 o’clock also allows a great deal of leverage applied from up top, especially with a round receiver body design. There is good reason bench rest competitors permanently glue barreled actions into stocks.
Solution: Angle-Blocktm Bedding System
A permanent glue-in bedding technique certainly works, but with obvious disadvantages. The Angle-Block Bedding System was derived more from the barrel block concept utilizing multiple cap screws provided as fasteners. We believe rigidity provided by multiple fasteners can be applied directly to the receiver and will be equally effective.
Two design features are important: first, use torx head cap screws. Remington style flat-heads when torqued only flare out the aluminum seats they rest in, possibly causing splitting. Furthermore, the torx head allows more torque without stripping out the heads. Secondly, and vital, engage the bottom of the receiver off of 6 o’clock to disallow twisting from forces occurring up top. To avoid unsightly elliptical holes in the bottom of the stock while accommodating this second feature, we arrived at our angle-entry design bedding blocks.
Two sets of threads machined in each of three pads located at the bottom of the receiver are angled to a common intersection point at the bottom of the stock. Each entry point at the bottom of the stock allows two action screws to be inserted one at a time into an aluminum-bedding block permanently bedded inside the stock, just like aluminum pillars. Once each screw is tightened to an equal torque setting, you have a total of six action screws arranged in a V-block-like formation. The entry ports in the stock are small enough for the rear set of action screws to be totally invisible with the trigger guard in place. It is noteworthy that recently more bolt-action rifles are being introduced on the market with extra action screws. We believe the Angle-Block Bedding System to be far superior to any other configuration available and applicable for any shooting discipline where top performance is desired.
Off-Center Recoil Surfaces
This theory was derived from Harold Vaughn’s Book: Rifle Accuracy Facts. In short, today’s bolt-actions during firing create recoil energy that is transferred to a surface well below center of bore, the origin of this energy. With all the mass above the center of bore subject to free movement during recoil, and the surface to absorb this recoil energy well below center of bore, an upward torque of the barreled action is occurring, actually trying to separate the barreled action from the stock. (An obvious example of this would be to shoot a conventional bolt action with the barreled action resting in the stock without any action screws.) The recoil lug placed below center creates the correct geometry for the barreled action to twist upwards in the stock. This twisting force is transferred directly to the action screw heads and threads in the bottom of the receiver, and in the case of poor glue-in bedding jobs, would be responsible for the breaking free of barreled actions from stocks. In fact, despite the relatively light recoil of the 6PPC, most bench rest actions feature a beefed up tang area with a square end providing the means to collect any upward “twisting” recoil energy.
Solution: Center-To-Bore Recoil Surfaces
We believe recoil surfaces that elevate right to the show line of the stock, or center of bore, are a definite improvement. The CST Model SCP action has two basic designs to create center-to-bore recoil surfaces; both are integral and machined into the receiver body, far superior to separately attached components. The Model SCP has an optional full 180-degree recoil lug, with surfaces, or “wings”, visible right at the show line of the stock. If the show line is not wide enough or if the integrity of the outer shell of a fiberglass stock needs to be maintained, the Model SCP standard recoil lug features grooves along its sides that stop right at the show line. This design is not visible once in the stock but provides two side surfaces much like splines to absorb recoil energy center-to-bore.