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Switch-out: changing your AR's caliber is as simple as replacing the upper receiver/barrel assemblies. Even if we're talking .338 Lapua.

AMONG THE MANY ADVANTAGES OFFERED BY THE AR-15 platform is its ability to swap upper receiver/barrel assemblies of different calibers among any standard-dimension AR-15 lower receivers. When I say "swap," I mean swap. Not "customize," not "modify." Swap. Assuming standard dimensions, you merely remove one upper receiver by pushing out the front and rear takedown and hinge pins to remove the complete existing upper receiver/barrel assembly (including bolt carrier and charging handle) and replace it with a different one. All you need extra are correct magazines for the new caliber.


The benefits are numerous. A typical basic .223/5.56mm AR-15 rifle or carbine will cost you from around $700 to well over $1,000, depending on manufacturer and configuration. An additional rifle in a different chambering (say, 6.8mm SPC or .300 AAC Blackout) will be at least as much and probably more, because the more exotic chamberings are generally priced higher. But you can buy a complete carbine-size 6.8mm SPC or .300 AAC upper receiver/barrel assembly for as little as $550 (depending on caliber and furniture configuration) and drop it right into your existing AR-15's lower receiver. An entire new dedicated heavy-barrel .204 Ruger precision varmint rifle will cost you at least $1,200, but varmint-grade 24-inch stainless heavy-barrel .204 Ruger upper receiver assemblies are available for as little as $640.

The "familiarity" thing is another benefit. You probably have your primary AR-15's lower receiver already rigged to suit your tastes. It's got the particular stock you like. You may have installed an aftermarket pistol grip. Perhaps it's got an ambidextrous (or left-hand) safety. And you may have installed a crisp, precision custom trigger. You've put a lot of effort and money into getting it to feel and work just like you want. Why start over? A new and different upper receiver/barrel assembly will drop right in, leaving you with a "new" rifle already rigged to operate to your taste. The new upper itself you can accessorize and scope to suit its purpose--just like you rigged your original upper for its intended use. Leave both uppers intact when you swap them; they're already sighted in and ready.

I have a lot of different AR-15s go through my shop, and I review them as-is. But for my own ARs, I've been building a collection of different-caliber, different-configuration upper receiver assemblies for several years, all used on only a couple of lower receivers that I've tuned and equipped to my own tastes. Both with left-hand safeties, of course. One is set up with a fixed stock and two-stage competition grade trigger for long-range accuracy purposes. The other has my favorite six-position stock and crisp single-stage trigger for hunting and home defense use. So whether I'm using a .223 upper for predators (either four-legged or two-legged), a 6.8mm SPC upper for whitetails or a .450 Bushmaster upper for bear or boar, they all feel the same to my hands.


Moreover, the interchangeability of the AR-15 upper and lower receiver system goes beyond mere "straight swap." AR-15 lower receivers are also capable of handling calibers and chamberings of far greater power and size than the platform's inventors ever imagined. For the past couple of years I've been spending a lot of time with the Zel Custom ( Tactilite T1 .338 Lapua AR-15 upper receiver assembly. You heard right. The Tactilite T1 is a .338 Lapua upper receiver assembly designed to operate on an ordinary AR-15 lower receiver (base price: $1,998).

I'm a .338 Lapua fan, and the Tactilite T1 is an impressive, unique product. It's essentially a single-shot, bolt-action .338 Lapua tactical sniper rifle that drops into any standard-dimension AR-15 lower receiver. It consists of a receiver machined as a single, fully integrated unit from a hardened 4140 steel billet with no welds. All critical features, including the Picatinny scope rail and lugs, are machined in and fully integrated with the receiver for accuracy and durability.

The fluted bull barrel is free-floated, and several options are available as to length (24-, 27-or 29-inch) and barrel manufacturer. The Ultralite Version has a chrome-moly barrel manufactured by Mossberg in Mexico. The Duty Version features a chrome-moly barrel manufactured by Lothar-Walther in Germany. The SuperMatch offers a stainless steel match barrel from Lothar-Walther or Lilja. Muzzles on all are threaded 1:14 and come standard with a high-volume gas brake.

The Ti's 7075 aluminum handguard is a hybrid smooth/quad-rail design. Designed to be side-loading and side-ejecting, the action has a push-feed bolt with a massive two-lug bolt head, Savage-style sliding extractor, plunger-style ejector and a large-size tactical-style bolt handle and bell. Available finishes include Black Cerakote, Parkerized and Type III anodized. It's heavy (thank God!), the Ultralite version coming in at 15 pounds.

Though much more massive than a standard AR-15 upper receiver, the Tactilite T1 nevertheless installs the same way as any other upper, by utilizing the lower receiver's existing takedown pins. However, because it's a single-shot bolt-action, not an AR-type semiauto, some changes to the lower receiver are necessary. These does not involve altering any dimensions, merely removing and/or replacing parts, and the task is well within the capabilities of anyone familiar with complete AR-15 disassembly/reassembly.

Specifically, you need to replace the existing hammer and spring with the supplied Tactilite versions of both and use Zel's anti-walk hammer and trigger pins (also supplied) to replace the standard pins. The existing trigger assembly disconnector and disconnector spring must be removed. Plus, the buffer retainer, buffer-retainer spring, buffer and buffer spring must all be removed to allow the manual bolt to move rearward into the receiver extension during cycling. And the bolt-stop assembly must be removed. Instructions are provided with the unit.

If these modifications are a bit beyond what you're comfortable doing yourself, well, that's what your local gunsmith is for. Of course, all this also means that you can't just lift off the T1 upper after installation and go instantly back to using a standard AR-15 upper, so most Tactilite users dedicate a lower to the .338 alone and employ one equipped with an adjustable noncollapsible stock such as a Magpul PRS (.338 Lapua recoil is a bit hard on most standard-type collapsible AR-15 stocks).

Is a massive .338 Lapua on top of a dinky little AR-15 lower receiver accurate? Is it durable? I said earlier I'd been living with one for a couple of years, and I've put a lot of rounds through it (including every type of commercial .338 Lapua ammo available in the U.S.) and a lengthy list of handloads--all on the same lower receiver, which shows no signs of wear or loosening. The main reason is that the Tactilite T1 recoil is surprisingly moderate. The muzzlebrake is remarkably effective, plus there's all that weight.

Accuracy? With the loads it likes, both commercial and handload, it's a sub-MOA shooter. I did replace the original standard lower-unit trigger parts with Timney Trigger's new Tactilite-specific trigger, which helped a lot.


A .338 Lapua upper receiver is admittedly not going to be something of interest to most AR shooters, but the basic interchangeability of the AR-15 platform should be. Why buy an entire new rifle when you can change the one you've got to a new caliber simply by pushing out two pins?

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Author:Metcalf, Dick
Publication:Guns & Ammo
Date:Oct 21, 2012
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