Thompson/Center Arms Dimension Rifle Review
Part 7 - Range Test
January 7, 2013

Thompson/Center Dimension Rifle Review

After evaluating the LOC Bridge Scope Mount Base in Part 6 of this review, I next wanted to evaluate the scope mounted directly on the receiver using the Weaver-style mounts provided with the rifle.  I reinstalled the Weaver-style mounts and then installed my Zeiss Conquest 4.5-14x50 Scope using a set of Burris Medium Height XTR Xtreme Tactical Rings.  I could have possibly used low height rings, but doing so may have made the scope too close to the barrel nut and potentially created a situation requiring the removal of the scope when changing barrels.  Because of the high cheek rest on the buttstock, I was pleased with my cheek weld for shooting the rifle with the medium height rings.  The two photos below show my rifle configuration for these range tests.

 

Figure 1
Thompson/Center Dimension Rifle Review

Figure 2
Thompson/Center Dimension Rifle Review

I initially bore sighted the rifle at 25 yards then fired some shots to dial in a basic zero prior to shooting at 100 yards.  At 100 yards, I shot a couple of groups working to finalize a zero. Next I wanted to evaluate the rifle's ability to return to zero when removing and installing the barrel while using a receiver mounted scope.  During my zeroing efforts, I shot my best 3-shot group in the .308 Win caliber which measured 0.42" .  The two targets below makes me believe that the Thompson/Center Dimension Rifle I received is 1 MOA capable as advertised in both .308 Win and .223 Rem calibers.  Clearly I'm showing my best groups, but after collecting data from multiple 3-shot groups, my group averages for both the Hornady .223 55gr HP Steel Match and Federal Premium Gold Medal Match 168gr SMK BTHP were just under 1" (0.98" and 0.97" respectively, see table below for summary).  I also feel that someone with greater shooting ability could possibly achieve better group averages.

     Figure 3 - .308 Win FGGM 168gr SMK BTHP       Figure 4 - .223 Rem Hornady 55gr HP Steel Match
Thompson/Center Dimension Rifle Review   Thompson/Center Dimension Rifle Review

During these next four groups, I removed and reinstalled the barrel between groups to see if there was any type of shift in zero.  Since I had several boxes of the FGGM on hand, I continued to shoot each of these groups with this ammunition.  My group sizes ranged from 1.30" to 0.91".  When you look at these shots collectively, they would produce a single group about 1" wide and just over 2" tall for the combined 13 shots.  The vertical scatter is probably due to trigger control on my part. Based on this evaluation, I would feel very confident swapping to another caliber and then back to this caliber considering these types of results.  This confidence is a must for this type of rifle and it looks like Thompson/Center did a good job with their engineering and quality control to make this happen.

Figure 4
Thompson/Center Dimension Rifle Review

Range Test Data

Ammunition Velocity (ft/sec) 3-Shot Group Size (in)
Average Std. Dev. Max Min Avg
Hornady .223 REM 55 GR HP STEEL MATCH™ 3080 26 1.53 0.26 0.97
Hornady .223 55gr V-Max 3119 25 1.56 1.02 1.22
Hornady .223 55gr G-Max Superformance 3156 28 1.27 0.67 0.92
Hornady .223 40gr V-Max 3539 41 1.39 0.48 .82
           
Federal Gold Medal Match .308 168gr SMK BTHP 2566 16 1.34 0.42 0.98
Hornady .308 155gr A-Max 2747 14 1.59 0.93 1.31
           

With the scope mounted on the receiver, I swapped to the .223 Rem configuration and went through another round of re-zeroing the rifle.  Before I re-zeroed for the .223 Rem, I first set my adjustable turret caps on my scope so that the "0" locations would mark my .308 Win zero.  The .223 Rem configuration rifle zeroed in with 1.5 MOA down adjustment and 7 MOA left adjustment.  With this configuration, I shot the Hornady 55gr V-Max and G-Max cartridges.  The G-Max gave slightly better results as shown in the table above.

When I compare my range results to those in a review by Guns and Ammo Magazine, I actually feel pretty good about my shooting abilities.  Overall my average group sizes were less than what they indicated in their article.  One thing that seems clear is that the slow twist rate (1:12") on the 0.223 caliber barrel could possibly produce tighter groups with a lighter bullet.  In the G&A review, the author was able to get a group average of 0.76" using some Hornady 40gr V-Max ammunition.

Another thing I noticed was that when you remove the barrel assembly from the stock, the two pins holding the trigger assembly in place and the pin holding the bolt stop lever in place would start to slide out of their holes.  Once I noticed this, I was careful to make sure they didn't drop out during a barrel change.  Clearly this is something you will want to watch when changing barrels in the field.

My next trip to the range allowed me the opportunity to study the .223 Rem caliber configuration further and the time to get some Hornady 40 gr V-Max ammunition for evaluation.  The next couple of photos show my range test configuration and bench setup.

Figure 5
Thompson/Center Dimension Rifle Review

Figure 6
Thompson/Center Dimension Rifle Review

During this second range test, the first step was to convert the rifle back to the .223 Rem configuration since my last shots during my previous range tests were with the .308 Win configuration.  It had been about 6 weeks between my first and second range tests and also it was about 30 degrees cooler for the second test, so I was a little conservative when I set up the 12" target shown below for my first shots of the day.  I dialed in my target turret offsets for the .223 Rem from my previous range test and then shot this 0.52" three shot group shown below.  Honestly, I was impressed.

Figure 7
Thompson/Center Dimension Rifle Review

I then swapped out the target and removed/reinstalled the barrel between each of the four groups shown below and I feel the results speak for themselves.  All 12 of these shots fall within a common rectangle about 1.32" wide and 1.28" tall.

Figure 8
Thompson/Center Dimension Rifle Review

Lastly, I changed back to the .308 Win configuration and dialed my turrets back to no offset and shot the group below.  This 0.61" three shot group fell about 1.25" to the right when compared to my groups (see Figure 4) with this ammunition.  At this point I started to consider this variability to potentially be a system variability which would also include the scope.

Figure 9
.308 Win at 100 yards with FGMM 168  gr SMK BTHP
Thompson/Center Dimension Rifle Review

 

Thoughts

Clearly both the .308 Win and .223 Rem configurations range tested are better than one MOA capable.  A very reasonable repeatable accuracy was proven when removing and installing the barrels multiple times for each caliber.  It is possible to use a single scope with multiple calibers as long as you record offsets and make ballistics tables.  I feel the key to using this platform will be selecting ammunition that shoots best in each caliber then creating an average zero for each caliber from a "group of groups" where you remove and reinstall the barrel between each group.

For more detailed photos and commentary, make sure you check out the other parts of this review and feel free to leave comments on my Reader's Comments page.  The following links are provided to help you see other parts of this review. 


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