A New Dimension: T/C Dimension

TC-Dimension_001Several American companies have offered switch-barrel rifles through the years, but none has come close to the commercial success of Thompson/Center. It all started in Rochester, New Hampshire, in 1967 with Warren Center’s Contender pistol. The action was eventually fitted with a buttstock and a longer barrel to give us the Contender Carbine. In 1983 a totally new single-shot rifle called the TCR 83 was introduced, and it was later improved a bit and renamed the TCR 87. The Encore came along in 1996.
Continuing T/C’s switch-barrel tradition is the bolt-action Dimension. Far more than a run-of-the-mill switch-barrel design, its Locking Optimized Components concept makes it virtually a switch-everything rifle.
Mega-Modularity
Barrels of various calibers can be interchanged, but so can the appropriate bolts and magazines for them. The system is chock full of excellent details that make the system easy to use. For example, all bolts and screws that are loosened during a switch are of captive design, which means they won’t mysteriously disappear as gun parts are prone to do. Tools required for going from one caliber to another come with the rifle.
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The stock is designed to be used with different families of component packages, with each part within a specific group identified by a letter of the alphabet. For example, barrels in .223 Remington and .204 Ruger are permanently marked “A,” as are the bolt, magazine and magazine housing that are compatible with them. The other components families are “B” (.243 Win., 7mm-08 and .308), “C” (.270 Win. and .30-06) and “D” (7mm Rem. Mag. and .300 Win. Mag.). The .22-250 requires its own magazine but uses a “B” housing. To prevent an incorrect parts combination, the bolt from one family will not work with a barrel from another family.
The blued chrome-moly barrels fit both right- and left-hand receivers and are 22 inches long for standard calibers and 24 inches for magnums, all with five-groove rifling. Bolt length is the same for all cartridges, but bolt travel is modified for cartridges of various lengths by machining the bolt-stop groove in the body of the bolts to different lengths—short (.223), medium (.308), a bit longer (.30-06) and longer still (.300 Magnum). The counterbored head of the bolt contains a spring-loaded extractor and a plunger-style ejector. A cocked firing pin is indicated by protrusion of the cocking piece from the rear of the bolt shroud.
The fluted body of the bolt is the same diameter as the locking lugs. The use of three lugs reduces bolt rotation to about 60 degrees, allowing a scope to be mounted quite low. It also increases the cocking cam surface angle, which requires a bit more effort to rotate the bolt compared with a two-lug design. The long handle with its large knob—along with an occasional dab of lubricant to the cocking cam surface—goes a long way toward making the bolt of the Dimension easy enough to operate.
The bolt is removed by first retracting it to the rear, then, while depressing the release located on the side of the receiver, rotating it clockwise until its handle touches the side of the stock, at which point it is free to be retracted completely from the receiver. When removing and installing the bolt, you will eventually scratch the comb of the stock with the sharp edge of the bolt shroud, at which point you will thank T/C for going synthetic rather than French walnut.
An AR Influence
Utilizing the AR-15 method of attaching the barrel allows ounces to be trimmed away by using an extremely light receiver machined from Type 7075 aluminum. The barrel is screwed into a 13/4-inch-long steel extension, which slides into the front of the receiver. The barrel is indexed to its proper position when a steel pin at the bottom of the extension engages a notch in the face of the receiver. Turning a nut—or torque collar, as T/C calls it—onto the threads of the receiver holds the barrel in place. Closing and rotating the bolt engages its locking lugs with shoulders machined into the interior surface of the barrel extension.
A conventional recoil lug is replaced by a better idea. A wide slot machined through the bottom of the receiver ring exposes a V-shaped surface machined into the bottom of the barrel extension. It mates with a steel lug of the same shape rising up from the floor of the stock, and the two are drawn tightly together when the front action bolt is tightened. In addition to resisting recoil, the “V-within-a-V” fit orients a barrel precisely the same each time it is removed and then reinstalled.
This, along with using the supplied tool to apply the prescribed amount of torque to the action bolts when installing the barreled action into the stock, ensures a return to zero when barrels are switched, and it also resists rotational force applied to the receiver each time the rifle is fired. The tang of the receiver rests atop an aluminum pillar embedded in the stock.
The fire-control system is the same as on the T/C Icon, and the bolt can be rotated with the two-position safety engaged. Trigger pull weight is user-adjustable within a range of 31/2 to five pounds.
The detachable, single-column magazines of all calibers hold three rounds that feed into the chamber as smoothly as greased pigs. Pressing a latch at the front of the magazine allows it to drop freely from the rifle of its own weight. The exposed latch with its light-tension spring is one detail I’d like to see improved. A bump while moving through brush or banging the rifle against the frame of a backpack could result in a lost magazine.
Sighting Arrangements
The Dimension comes with a two-piece, Weaver-style base attached to its receiver. Since points of impact will differ for barrels of different calibers, a scope with accurate repeatability of adjustments will make life easy. You simply zero the scope for one of the barrels and then record windage and elevation corrections that have to be made when the other barrel is installed. Another possibility is to have one scope zeroed for the .308 deer barrel and a scope of higher magnification zeroed for the .223 coyote barrel. Although the Weaver-style mount is renowned for its ability to return a scope quite close to zero when it is removed and reinstalled, a few confirming shots on paper before heading to the hunting grounds are still a good idea.
Available at extra cost is a bridge-style mounting base, the front of which clamps securely to slotted dovetail cuts in the top of the barrel. Its rear end is vertically split into two parts, one of which attaches to the receiver. To use it, the two-piece base that came attached to the rifle is removed, and screws from the rear section are used to attach the rear base of the bridge-style mount to the receiver. After it is installed, a large bolt draws the two halves together.
Attaching a scope to each barrel is convenient, but this system does position a scope much higher off the rifle than the standard base. Because the receiver wall is quite thin, there are not many threads in two holes drilled and tapped for the bases, so regardless of which mounting system is chosen, the screws should be coated with liquid thread lock prior to installation. Otherwise they will quickly vibrate loose.

 

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