TAC21 Review (TAC21/TAC21LA)

TAC21 308 Win (front) and TAC21LA 300 Win Mag (rear).

Modular Driven Technologies TAC21 and TAC21LA Chassis Systems

When we first heard about the TAC 21 Chassis system by Modular Driven Technologies (MDT) it immediately caught our attention.  A chassis system that gives a Remington-700 the handling characteristics of an AR-15 while allowing the use of detachable AICS box magazines and improving accuracy,  seemed like a tall order.  Designed for Remington-700 style actions, the TAC21 and TAC21LA provide the user with a continuous top mounting surface with a 20-MOA cant.   The TAC21 and TAC21LA also allow the operator to install modular sections of picitinny rails on the forearm and side of the chassis.  End users can either use lightweight polymer rail sections from Magpul or aluminum extensions (that include a QD sling attachment point).

Brownells shipped us an action, barrel, TAC21 chassis system as well as all ancillary items to get the TAC21 up and running.  Modular Driven Technologies reached out and provided us with an additional TAC21 short action chassis and their new long action chassis, the TAC21LA. The TAC21 accepts short action 5 and 10-round AICS magazines while the TAC21LA, accepts the 5-round 300-Win Mag AICS magazines.

For the short action chassis, we built a .308 on a new receiver.  To test the long action TAC21LA, we used the barreled action from a Remington-700 Sendero SF II 300 Winchester Magnum that we were recently sent to evaluate.

Short Action: Our Remington-700 Short Action came coated in Fail Zero’s EXO proprietary coating.  The EXO coating provides lubricity and weather protection for the blued receiver.   We also selected a Shilen Match Grade 1:10′ twist 30-caliber #7 contour barrel as well as Holland recoil lug.  The action was blueprinted and the the barrel installed to a finished length of 25″ with a surefire brake installed on the end.  Please note: Holland lugs are over-sized with a slightly different profile then the factory Remington lug.  If you plan on using one in the TAC21 chassis, the receiver will have to be modified and the lug needs to be trimmed to length.  Modular Driven Technologies does NOT recommend that you modify the chassis because you can potentially weaken it.  MDT now offers their own over-sized lug for the Remington profile that is a full .300″ thick to address this.

Long Action: The Remington-700 Sendero SF II  is a varmint contoured, heavy barreled, hunting rifle offering hunters extreme accuracy for long range shots.  With a stainless steel action and barrel, the rifle comes from the factory in a fiberglass stock with an aluminum bedding block and coated in a spiderweb texture.  Our text rifle was chambered in .300 Win Mag and had a 26″ fluted stainless steel barrel.

TAC21 .308 Win (left) and TAC21LA .300 Win Mag (right).


Constructed entirely of hard anodized aluminum, installation of the TAC21 and TAC21LA is fairly straight forward.  It requires you to remove any optics, rings and bases as well as your current stock.  You then need to remove the trigger and bolt catch from your action.  MDT provides small slave pins to help accomplish this.  You then slide the new action into the receiver, reinstall the trigger and install the trigger guard and action screws.  The forearm is secured with three Allen screws and the buttstock is secured via a QD cam.  Select your favorite AR-15 pistol grip and buttstock and you are ready to go. A complete overview of the installation process is covered in the video at the bottom of this page.

TAC21 as supplied.
AICS magazines, (left to right) 5 round 308, 10 round 308, and 5 round 300 Win Mag.
TAC21 and TAC21LA aluminum rail sections.  Available in 3.8″, 5″ and 6.5″ lengths.
Aluminum rail section with QD swivel attached.  The 5″ and 6.5″ models accept QD sling swivels.

Preparing for evaluation:

For the TAC21 in .308, we selected a Magpul CTR buttstock on a VLTOR mil-spec receiver extension.  We utilized a BG-17 over-sized battle grip and topped the rifle with a Leupold Mark-4 4.5-14x50mm M1 Mil Dot scope in a ADM Recon mount.  The TAC21LA was equipped with a standard AR A2 grip, Generation 2 Magpul PRS stock and a Leupold Mark-4 3.5-10×40 M1 TMR scope in GG&G Accucam QD mount.  We selected Federal Gold Medal match grade ammunition for both rifles, utilizing the 168 grain SMK in 308 and the 190 grain SMK offering in 300 Win Mag.

Magpul CTR with 1/2″ riser (top) and Magpul Generation II PRS (bottom).
TAC21LA .300 Win Mag equipped with Magpul PRS stock, A2 pistol grip, Harris bi-pod and Leupold Mark-4 3.5-10x40mm M1 TMR scope in a GG&G mount.
TAC21 .308 Win with CTR stock with 1/2″ riser, VLTOR extension, Leupold Mark-4 4-14x50mm M1 Mil Dot in an ADM Recon mount.
TAC21 stock cam locked position.
TAC21 stock cam locked position.
Rotating the locking cam counterclockwise releases the stock adapter.
The user simply slide the stock and stock adapter off the rifle. This allows the user to remove the bolt or break down the rifle for transportation.

On the firing line:

The TAC21 and TAC21A give your bolt rifle the ergonomics of your AR-15;  settling in behind the guns, you feel right at home.  For evaluating accuracy, we shot the rifles, prone,  off of Harris bi-pods with a rear bag for support. Temperature was 80F with 80% humidity and gusty full-value 15-mph winds.  Firing the TAC21 and TAC21LA, we found that having the bore axis directly inline with the stock managed to tame recoil and bring the gun back on target quickly.  While this was true for both rifles, the .308 TAC21 also had a Surefire brake, which cut perceived recoil significantly.  This combination easily made it the most comfortable .308 bolt gun any of us have ever fired.  Equipped with a PRS, the TAC21LA was a pleasure to shoot.  Having shot the same rifle for evaluation purposes three days earlier in its as-issued stock, this was a pleasant surprise.

Rifle controls were easy to access.  The safety, while housed in a recess in the chassis, was easy to engage and disengage.  Initially, we were a little concerned that the recessed design of the safety selector would be hard to manipulate with it is access from the side, rather then the top like on a traditional configuration.  The magazine release worked well and was easily accessible.  The standard bolt handle worked just fine with the chassis.  While over-sized bolt handles are nice and do tend to speed manipulation, we didn’t find it necessary on our test guns. The magazines fed and functioned well.  In the past, we have noticed some bottom metal in conventional stocks can casue rounds to hang up on the bottom of the action during the feeding process.  We did not have that problem here.

The #7 contour, coupled with the lightweight of the CTR  stock, made the TAC21 feel slightly front-heavy.  We think that this combination would be ideal on a 20″ barreled gun.  The PRS on the TAC21LA balanced well.  During the bore sighting process, we removed the stock from the TAC21LA .300 Win Mag and didn’t torque the stock adapter cam enough and the stock loosened up a bit during firing; this was immediately remedied by applying more torque to the cam.

The TAC21 and TAC21LA did provide an accurate platform for our actions with the TAC21 shooting slightly over 1/2 MOA (see photo below) and the TAC21LA shooting sub MOA (see photo below).

TAC21 .308 Winchester’s first 3-round group of the day. Accuracy was consistently sub-MOA.
TAC21LA .300 Win Mag. 3 -rounds 1/2 hour after our initial 1-round zero. The TAC21LA tightened up the accuracy of the Remington-700 Sendero SS II.
TAC21 chambered in 308.

Overall Impressions:

  1. The TAC21 and TAC21LA provide AR type ergonomics to bolt rifle shooters.  This is especially beneficial to shooters like us, who have logged far more rounds on AR-15 type platforms then any other. Consistency is the key to accuracy and proficiency.  The TAC21 and TAC21LA were both exceptionally easy to handle in field firing positions.
  2. The TAC21 and TAC21LA are accurate chassis to build rifles on.  We found our 1/2 MOA .308 and sub MOA .300 Win Mag as evidence of this.
  3. The inline stock design helps control recoil and aids in quicker follow-up shots.
  4. The removable buttstock was a nice feature.  Initially, we were a little skeptical about having to remove the stock every time we wanted to remove the bolt.  In practice, this only took seconds.  Additionally, removing the stock made the rifles easier to transport in short cases and when storing in a safe.
  5. The continuous 20-MOA top rail provides an excellent base for shooters, especially Mil/LE, to mount night vision optics in front of their day scopes.
  6. The ability to select and change stock and pistol grip configurations was especially nice.  It allows the end user to test out a variety of configurations before settling on one he prefers.  We especially liked the CTR stock with riser.  This was a nifty stock configuration for a bolt rifle.
  7. The ability to add modular grip panels to the front sides of the chassis provides further possibilities to equip the rifles based on mission-specific needs.  When we first received the TAC21, we ended up bolting pretty much everything we had laying around on to it.
  8. Suggestions for improvement; redesign the system so that the trigger does not have to be removed and add some sort of locking mechanism on the cam that secures the stock adapter.  If the cam wasn’t thoroughly torqued, it comes loose.  The chassis functioned well and neither of these items are deal breakers, but we would like to see them improved.

This is a well thought out chassis system that provides AR ergonomics, an uninterrupted 20-MOA rail and a detachable magazine to your Remington-700 rifle.  You can read more about the MDT TAC21 and TAC21LA on their website.   You can purchase the TAC21, TAC21LA as well as well everything else you need to get your rifle up and running, including ammunition, at Brownells.