The Dimension is, as T/C likes to say, really more of a system than merely a rifle. Using what the company calls its Locking Optimized Components, users can switch not only barrels but just about everything else on the gun. T/C personnel envision different stocks and barrel contours for the future. For now, 10 different chamberings are available in standard configurations. Every caliber works with the same receiver and stock and, if the user desires, the same scope.
At the heart of the Locking Optimized Components lies a system of interchangeable barrels designed to be switched out by the end-user with a simple tool; it’s made all the more simple by nomenclature.
Cartridge-group parts—the steel barrels and bolts, and polymer magazine kits—are identified by a letter: “A,” .204 Ruger, .223 Rem.; “B,” .22-250 Rem., .243 Win., 7 mm-08 Rem., .308 Win.; “C,” .270 Win., .30-'06 Sprg.; and “D,” 7 mm Rem. Mag. and .300 Win. Mag. To switch from one cartridge group to another, users need the entire group of parts. But switching within letter groups requires only a barrel. So switching from .204 Ruger to .223 Rem. is pretty quick. The system is fairly foolproof, too. Components for caliber families are labeled with their appropriate letters; different letter group components will not work with one another.
Complete caliber interchanges can be made in minutes with a bit of practice. The secret lies in the use of a barrel nut, the same system used on the AR-15. The sight of a barrel nut was made famous on sporting rifles by Savage in the 1950s. It’s inexpensive, repeatable and it works fabulously. When Savage introduced the barrel nut, it smoothed its lines, essentially hiding it. Thompson/Center eschewed the practice, choosing instead to make the barrel nut large and knurled.
The barrel is screwed into an extension that slides into the receiver; it indexes when a pin in the extension engages a notch in the receiver; it’s secured by tightening the barrel nut around the receiver. Clearly, this means the barrel is free-floating, which aids accuracy. What’s more, the extension is mated to the chamber and bolt with such tight tolerances that every bolt of a given cartridge family will headspace correctly. So while 10 chamberings are presently offered (and numerous others may be offered in the future), only four different bolt sizes are needed to serve them all.
Closing the bolt engages three locking lugs against shoulders in the barrel extension. That arrangement makes for a bolt throw of about 60 degrees. A conventional recoil lug is replaced by a robust slot/lug system with a bedding block that mates the barrel to the stock; the pieces are drawn together through the receiver with a torque wrench (included with the purchase of every complete gun) that tightens the front action screw. This slot/lug system also indexes the barrel precisely every time it’s removed then replaced.
The blued, chrome-moly barrels fit right- and left-handed receivers (yes, left-handed Dimensions will be available soon). Standard-caliber barrels are 22-inches long; magnums measure 24 inches; all have 5R rifling. All are standard taper for now, but the company envisions various profiles offered as options in the future.
Since no stresses bear on the receiver upon firing, it’s machined from aluminum. It weighs a mere 12 ounces. Its top and bottom are rounded, and it measures 7 5/8-inches long and 1 1/2-inches in diameter, large enough to accommodate even larger-diameter cartridges in the future should demand warrant them. As it’s an aluminum cylinder with rather thin walls, the additional metal left in the final cut adds rigidity, which reduces the effects of torque during recoil and thus aids accuracy. An ejection port is cut only on the right or left side (depending on whether it’s a right- or left-hand rifle); it measures 3 1/8-inches long and 11/16-inches high. I experienced no failures to eject spent cases when firing hundreds of rounds through various prototype and early production rifles during the past year-plus.
Bolt length and diameter is the same for all cartridges, but bolt travel is modified for short (A), medium (B), long (C) and longest (D) cartridges with a groove in the bolt body. Bolts are one-piece. Only the diameter of the bolthead varies among the four families. Each is fitted with a Sako-style extractor and plunger ejector. Each is fluted and the same diameter as the locking lugs. To remove the bolt, pull it rearward, and while depressing a release on the left rear of the receiver, rotate it clockwise, turning it upside down before removing it completely from the receiver.
The single-stage trigger, borrowed from the Icon, is user-adjustable from 3 pounds, 8 ounces to 5 pounds. The pull weight on our test unit averaged 4 pounds, 2 ounces from the factory. It uses a two-position safety; the bolt can be worked with the safety engaged.
The detachable magazine is polymer. It’s a single-column design that holds three rounds in all calibers. Magazines are adaptable to different calibers with the use of an insert (think “magazine well”). One is included with the purchase of every new barrel, though users need different ones only when switching between caliber families. I experienced no problems with feeding from the polymer unit.
Thompson/Center envisions an optional stock as part of the Dimension system in the future. I’ve heard about a green synthetic version with a straight comb. That would be a good alternative. I have to admit that I do not like the present stock, a black synthetic unit with a high comb and a scallop that runs the length of the buttstock’s underside from pistol grip to heel. I’ve never been a fan of the Monte Carlo design. This stock takes the look to new limits, conjuring images of Molly Hatchet album covers. Still, I need to note that it’s not all about appearance; the high comb is necessary given the large-diameter receiver that positions a scope a bit higher than optimal on an otherwise similar rifle.
Recoil is not unlike that in any other gun when shooting the “A,” “B” and even the “C” calibers. But I noted something “special” when shooting the “D” calibers. Recoil is not unbearable in the Dimension. It will only become a problem if larger calibers (perhaps the .375 H&H Mag.?) are released with the same stock design. In that case, I’d like to see the alternative on the drawing board at T/C headquarters.
The barrel channel at the fore-end is wide to accommodate all barrel contours, both present and planned, which might be offered for the rifle. That eliminates the need to design multiple stocks for various caliber groups with different barrel contours. It’s so wide it reveals the mold marks even from afar—and could collect water and snow in inclement weather. That channel reveals plainly that the barrel is free-floated, which isn’t an altogether bad selling point.
A molded trigger guard and steel sling swivel studs are integral to the stock. Rubber panels on the pistol grip and fore-end provide purchase for a shooter’s hands. They’re pliable but not too squishy, and their bullet-shaped, raised ribs complete the gun’s overall industrial look. A generous rubber recoil pad covers two synthetic plates that are removable to adjust length of pull between 12 1/2 and 13 1/2 inches.
Complete Dimension rifles come with two-piece, Weaver-style scope bases installed on the receiver. When changing calibers the scope stays with the receiver. Of course points of impact will differ between chamberings, so users need to check zeroes when changing barrels, though in range tests I noticed remarkably close groups thanks to the barrel lockup system that ensures repeatability.
Alternately, users may choose to buy separately a bridge-style scope mount ($88) that makes the Weaver bases and rings obsolete. Its front end clamps to a dovetail in the barrel. Its rear end is split vertically; one half attaches to the receiver via two machine screws that tap into the receiver. Picatinny-style slots atop the bridge mate to rings available separately (steel 1-inch rings are available from T/C). With this system the scope stays with the barrel; T/C claims subsequent groups to return within an inch of zero.