August 13, 2012
By G&A Staff
On the front page of the Thompson/Center Arms website for the new T/C Dimension it says: "Three shots into one inch at 100 yards. Guaranteed." Even with the parenthetical caveat requiring the use of premium ammo to meet that guarantee, those are strong words from any rifle maker. For a swap-barrel, interchangeable-caliber bolt-action rifle they are particularly strong.
And that's exactly what the new T/C Dimension is: a radically new bolt-action design that offers complete interchangeability among 10 different cartridges in four separate cartridge families initially running from .204 Ruger to .300 Winchester Magnum.
To swap between cartridges within one family all you need is an additional barrel; the magazines and bolts are the same. (There is one exception; the magazine group for the .22-250 is a standalone.) To swap between cartridges in different families, you'll also need the correct bolt assembly, and a magazine housing and magazine for that family's cartridges. All barrels, bolts, and magazine groups work interchangeably with the standard Dimension receiver and stock assembly.
Moreover, Dimension receivers are available in either right-hand or left-hand versions, and either style receiver will accept any Dimension barrel and work perfectly with any Dimension bolt or stock.
The interchangeability is complete. All tools necessary to make any of these swaps come standard with each Dimension rifle. A complete one-family-to-a-different-family cartridge swap will take about 10 minutes the first time you try it. About five minutes after that.
Current Series A Dimension cartridges include .204 Ruger and .223 Remington. Series B includes .22-250 Remington, .243 Winchester, 7mm-08 and .308. Series C cartridges include .270 Winchester and .30-06. Series D includes 7mm Remington Magnum and .300 Winchester Magnum. More choices will be added to all groups as demand warrants.
All interchangeable parts, including barrels, bolts, magazine housings and magazines are boldly marked with the letter of their family to prevent accidental mixing of parts when switching between calibers or groups. All Dimension magazines have a three-round capacity.
Should anybody be surprised that Thompson/Center has introduced a caliber-interchangeable bolt-action rifle? Not really. After all, T/C styles itself as "the company which perfected interchangeability." T/C's reputation was founded on the instant-swap simplicity of the original Contender break-open single-shot pistol, and that reputation has continued through the subsequent and hugely successful G2 Contender and Encore lines of pistols, rifles, shotguns and blackpowder models.
In fact, one of the first comments I heard when T/C introduced its first bolt-action centerfire, the Icon, back in 2005, was "How long do you think it'll take them to bring out an interchangeable version?" Answer: a while, as it turned out.
But the Dimension is in no way anything like the Icon or any of the other bolt-action models now in the T/C line. It is truly something new, which you don't see a lot these days. Let's take a closer look at some of the details and specifications.
The first thing anyone remarks on when they first see a Dimension is the synthetic stock. Comments range from "Wow! Star Wars!" to "What is that thing? A humpback whale?" There's no question there's nothing traditional about it, either in appearance or design, but it's built with a purpose.
It's synthetic, for weather-imperviousness and to accommodate the unique receiver/barrel bedding system. The oversize free-float fore-end channel will accommodate any diameter Dimension barrel in any chambering, including the yet-to-come bull-barrel versions.
The gray polymer "traction panels" on the fore-end and pistol grip ensure a secure grasp. The arched contour of the buttstock raises the shooter's head to a correct level for quick optics acquisition and reduces stock drop to allow better alignment of the shoulder with the gun's axis of recoil.
The Dimension stock is functionally so "straight-line" (which sounds silly, I know, considering its look) that the bolt handle must be rotated completely past vertical in order to clear the front of the comb when removing it. Moreover, there is a thick, soft rubber recoil pad and two half-inch spacers for customizing length of pull. The overall effect is remarkably comfortable to fire, even with the heavy-recoiling calibers. It's engineered for use, not looks.
The Dimension's bedding system is also unique. The receiver/barrel assembly is held into the stock by two captive screws in the stock: One threads into the rear of the receiver; and one threads into the rear extension of the barrel itself, which is pulled down into an aluminum bedding wedge that's molded into the stock. This wedge interface completely eliminates any possibility of rotation or lateral shift of the receiver/barrel assembly within the stock.
The barrel and receiver themselves are held together by a threaded Torque Collar that allows barrels to be interchanged in the first place. All these parts can be loosened, tightened, removed, replaced, changed by the user only by employing the dedicated tools T/C supplies with each Dimension. This ensures correct assembly and precisely correct torque on all screws and nuts, for perfect repeatability of the gun's performance across calibers.
The Dimension also has an adjustable trigger (3.5 to 5.5 pounds), and an adjustment tool is provided. The adjustment is accessed by removing the bolt.
The bolt handle is angled and sculpted for easy operation, and the receiver has a two-position thumb safety. Each Dimension rifle comes equipped with Weaver-type two-piece receiver mount bases for optics. A bridge mount that also attaches to the barrel is an optional accessory (more about that later). Sling swivel studs are standard.
The three-round magazines are polymer and drop freely from their housing via a simple latch lever at their front. They are not flush-fit but nearly so. All barrel muzzles are recess-crowned to protect the rifling. All accessory Dimension barrels come with appropriate magazine and magazine housing insert.
This is not a "how-to" article, so I'm not going to go into extended detail describing the exact step-by-step procedure for switching Dimension barrels or cartridge families. A very well-presented, well-illustrated guide accompanies each rifle and is available on line at DimensionRifle.com.
Familiarize yourself with it before you start, and if you follow the instructions in order, it will be a very easy task. If you do things out of sequence, you won't break anything, but it won't come out right, and you'll have to go back and do things in the correct order.
Here's a simplified breakdown. Remove the magazine and the bolt. Remember the bolt has to be "over-rotated" using the bolt release latch to clear the comb of the stock. Take it out and put it back in a few times just to get the feel.
Use the supplied torque tool to loosen the stock screws and remove the receiver/barrel assembly from the stock. The screws are captive, so you won't lose them. Pluck the polymer magazine housing from the inside of the stock. Remove the rear bridge mount screw from the receiver end if you have a bridge mount installed.
Next, use the provided leverage tool and torque tool to loosen the torque ring holding the barrel to the receiver (it's easy). Remove the torque ring completely, and separate the barrel from the receiver. The Dimension is now fully dismantled.
To reassemble with a different caliber from a different family, just reverse the process. Slide the new barrel onto the receiver (there's an index tab; you can't do it wrong). Retighten the torque collar all the way down using the leverage tool and torque tool. Reattach the rear bridge mount screw if you're using a bridge mount.
Put the correct magazine housing into the stock and fit the receiver/barrel assembly back into the stock, using the torque tool to properly tighten the screws. Install the correct bolt back into the rifle. Voila!
Okay. The Dimension comes apart and goes back together really easy. Changing barrels and cartridge families is really easy. The engineering design is innovative and elegant. The system is as user-friendly as I can imagine. It has an adjustable trigger. Kudos to all involved. But does it shoot?
The key to any interchangeable-barrel/interchangeable-caliber firearms system is dependable, repeatable accuracy. That's why most such systems provide a mechanism for mounting their optics on the barrel, so that nothing about the system's zero is disturbed when taking barrels on and off. That's why the Dimension system offers a barrel-attached optics bridge mount — but only as an accessory, not as the standard item. The standard mount system provides a two-piece receiver mount system.
Okay. I understand. If you want to leave your .223 Dimension barrel all pre-zeroed when you take it off, you just buy an accessory bridge mount, zero your scope, and leave it attached to the barrel between swaps. Same with any other barrel you acquire.
If you only have one scope, however, you're probably going to want to leave it on the gun and just re-zero it when you switch cartridges — like from .243 to .30-06. Those happen to be the two calibers I received in my Dimension review package. But I didn't get a bridge mount, and they couldn't get me one in time to make this deadline. (Nor a left-hand receiver, either. Drat!)
I already knew the Dimension system was repeatable using a bridge mount because at a T/C introductory seminar for the Dimension last year I had done a repeatability exercise using a .223 barrel in which I shot 100-yard groups with a zeroed .223 with bridge mount, then took the barrel/scope assembly off the receiver, replaced it with another barrel from a different cartridge family, and let other shooters work that setup for a while. Then I put the .223 barrel/scope assembly back on the same receiver and shot groups into the same targets I'd used before. The second groups superimposed over the previous ones. Proof enough.
But this time I was curious about what the effect of removing and replacing Dimension barrels would be with a receiver-mounted scope. If the system really works as advertised, if the bedding and torque-tool system is really consistent, one would expect very little variance in point of aim after removing and replacing a barrel on a receiver with an already zeroed scope.
Also, if the scope mounts were high-quality quick-detach items, you'd expect to be able to remove and replace both with very little re-zero required.
In order to test this, after I finished my five-load 100-yard accuracy test with the Dimension's .243 Winchester barrel, I shot a four-round (full-magazine plus one) carefully zeroed group at 100 yards, then saved the target and swapped the Dimension to .30-06 configuration for that accuracy test.
I did not change the settings on the receiver-mounted Nikon Monarch 6-24X scope I was using for both cartridges, just left it sitting on the receiver without any re-zeroing. I was only interested in group size, not point of impact, and the .30-06 ammo was shooting only about five to six inches different point of impact from the .243's zero settings at 100 yards anyway.
After completing the .30-06 accuracy test, I swapped the gun back to the .243 barrel, still with the Nikon scope on the receiver, zeroed just as it had been when the .243 barrel came off. I fired another four-round group at the original target. The before and after images accompany the article.
Excluding the one called flyer (me, not the gun) which opened up the second four slightly, the displacement of the two groups — one before the barrel swap and 75 intervening .30-06 rounds, and one after — was less than 0.25 inch. The overall groups size grew by only 0.18 inch. I'd call that pretty consistent and repeatable.
The overall accuracy results with all loads from both calibers? Check out the accompanying chart below. I'd certainly say they meet Thompson/Center's accuracy guarantee.