Futureproof Frankenbolt Trainer Rifle

Train Your Kin and Treat Yourself With a Barrel Nut-Based Bolt-Action Build

The AR-15 has long reigned as the rifle world’s king of adaptability. Its ambitions were unchained when the bonds of intellectual property rights were cut, and its rise to the throne was supported by a court of manufacturing barons and an army of consumers eager to reap the same reliability and interoperability enjoyed by our nation’s military forces.

The thing that really brought consumers to the AR was the platform’s abandonment of the gunsmith. The industry tacitly agreed to follow the conventions and dimensions approved by the U.S. military and, in doing so, eliminated the need for metalwork fitting when assembling or reconfiguring finished parts into a working rifle.

There’s no universally agreed-upon bible for bolt guns, but the closest thing is the unwritten gospel of the Remington 700 action. Its critical dimensions are commonly used to make so-called clone actions that mate up with 700 compatible barrels, stocks, chassis, triggers, magazines, and scope bases. To that end, there’s been a recent surge in the popularity of pre-fit barrels that don’t require a gunsmith, or their weeks-long wait times, for installation. Thus, we have the rise of the bolt-action frankengun.

The cornerstone of the frankenbolt build are manufacturers that hold tolerances so tight on their actions that equally fastidious barrel manufacturers cutting steel in a different zip code can produce shouldered barrels that spin on those actions and maintain perfect headspace dimensions. Not only does this reduce consumer wait times for new and replacement barrels, the economies of scale involved in making dozens of barrels at a time theoretically reduces their cost. Instead of a lathe and years of machining experience, the end user needs only a vise and a way to tighten the barrel and action together, preferably while applying the manufacturer’s specified amount of torque.

We think Bighorn Arms 12-point DLC-coated barrel nut looks great, and it’s easily installed with a common 1 1/8-inch box-end wrench.

Taking the savings on barrels a step further, pre-fit barrels can be had without shoulders. These require a jam nut to secure the barrel to the action, leaving the final headspace adjustment to the end-user. Beyond the vise, action wrench, and torque wrench needed to install a shouldered prefit barrel, this barrel nut setup requires the addition of a barrel nut wrench and a set of go- no-go gauges to set the rifle’s headspace. Fire-formed brass works, too.

Taking the DIY aspect of the barrel-nut bolty into account, it’s the perfect platform on which to build a practical precision competition training rifle, especially one that’s adjustable to fit young shooters and easily reconfigurable as calibers and needs change. So, that’s what we’re using in this article.

When your progeny outgrows their 10-22 and they’re ready to join you at a precision match, you could buy them a nice, off-the-shelf, centerfire rifle. Or, you might cherish sitting down with them to research and choose parts for their first “real” rifle. And more memories are on tap as you help them assemble it at home and finally proof your shared ambition on the range.

Plus, if your teenager’s ambitions turn away from practical precision rifle competition, hopefully in favor of studying brain surgery or international finance, you’ve built a kick-ass training rig or backup PRS rifle for yourself. Also, your barrel nut Rem 700 clone is easily re-barreled or reconfigured for any bolt-action role, from hunting to bench rest competition, since it accepts the huge range of R700 aftermarket parts and accessories.

Shank

When going down the pre-fit barrel path, the first decision to make is which barrel thread pitch camp to join. There are two main choices, the Remington 700’s native 1-1⁄16 inch x 16 tpi and the Savage small shank standard that measures 1-1⁄16 inch x 20 tpi.

Savage popularized the bolt-action barrel nut, so there are many options for barrels available in the Savage small shank threading. Pre-fit Remington barrels are a bit more rare, but they’re out there. They’re often called a Remage setup — a Remington thread pitch with a Savage-style barrel nut. There’s no real performance advantage when comparing the two, but there are more actions, barrels, and barrel nuts to choose from if you join team Savage small shank.

Action

Case in point — we settled on the Savage small shank-compatible Bighorn Arms Origin action for our frankenbolt trainer build. It’s the same cost or slightly less than buying a trued and blueprinted R700 action. It really doesn’t make any sense to go that route when the Origin also includes a host of performance, reliability, and configurability upgrades not found in a basic 700 action.

We wept a tear for the tried-and-true Atlas bipod initially installed on the rifle, but swapped to the ZroDelta Warhammer setup because it was easier to for our young shooter to deploy.

The Origin’s floating bolt head is easily swapped to change calibers; it also has controlled round feed, a burly extractor, and a mechanical ejector. It shares the footprint of a standard 700 action, so there’s no end to the number of stocks and chassis it’ll fit; it also accepts industry-standard AI footprint magazines.

Barrel

As a training rifle meant primarily for use by a pre-teen stepping up to his first centerfire rifle, we wanted it to be as friendly as possible, both in terms of recoil and ammo expense, so we chose a 223 Remington chambering for its first incarnation. Even the cheapest ammo will provide good training reps on steel inside a few hundred yards, and there’s no shortage of high-end .223 ammo choices in when it’s time to tighten up those groups.

We chose one of Hawk Hill Custom’s heavier Marksman barrel profiles for the weight it lends in recoil reduction. Thanks to the beefier barrel profile, the gun handling experience is akin to a full caliber competition gun. We hate math, so we just agreed when the guys from Hawk Hill suggested 1:7.5-inch twist rate. We figured it’s a middle ground that would work well enough with longer, 70-grain .223 bullets while still sending the cheap 55-grain rounds where we want them to go.

We could have gone to a 24- or 26-inch barrel for maximum velocity, but we wanted to build a pussycat that’d purr and cuddle with a new shooter. So, we chose to combine a shorter barrel length with a silencer to make an easily wielded rifle.

Timney’s Calvin Elite Custom trigger allowed us to fine-tune the length of pull and shoe shape for smaller hands.

This results in a package that a 12-year-old can lift and guide through multiple shooting ports on a PRS-style competition stage without getting frustrated.

Replace the Origin’s 223-sized .380 bolt head with a standard-sized .478 bolt head for $125, spin off the 223 barrel and install your favorite flavored 6mm competition barrel, and the gun’s big-boy match-ready. If you’re careful, you can swap barrels without even pulling the scope off the gun, though no manufacturer will recommend it for fear of angry phone calls about crushed scope bells. Our scope-on caliber changes take about 20 minutes, and the new barrel’s zero is usually within an MOA of the original barrel’s zero.

Ergos

One of the chief concerns in building a rifle meant to accommodate growing hands is adaptability. Sure, this seems like an obvious point, but there are two ergonomic considerations that’ll drive this train: length of pull and cheek comb height. Since we’re training smaller people, we have to focus on shorter stocks with tall cheek combs.

Grayboe’s Ridgeback stock has a 12.7-inch length-of-pull out of the box, short enough to fit a mini-me. Stack the four included spacers and gain an inch to fit a full-size biped. We like the Ridgeback’s wide, flat fore-end, its upright grip, and its flat, bag-riding keel. You’ll notice we did some old school modifications to the cheek riser to get the height to match up with the 34mm scope. This, despite using rings that left a comfortable but minimal space between the scope and the barrel. Hundred-mile-an-hour tape and some high-density foam from a craft store put the cheek piece where we needed it. Par for the course when trying to make a big boy gun for a small fry, we suppose.

Timney’s Calvin Elite Custom gives us another, welcome ergonomic adjustment that’s not very common on 700 triggers. It comes with a few trigger shoes that slide fore and aft, and also rotate slightly. It lets us slide the trigger shoe pretty far to the rear of the trigger guard, a perfect way to shorten the reach for smaller hands.

Not only could we use the sliding trigger shoe to dial in the last bit of the length-of-pull, but the Calvin Elite Custom is customizable with the array of included trigger shoes. They’re easy to change, and giving the kid the choice of shoes gives them more feeling of ownership and pride in the rifle.

Bolt head swaps for caliber changes are simple, as is maintenance, with the Origin’s bayonet-style firing pin assembly.

We left the single stage adjustment at its max weight of 2.5 pounds for our little guy to learn on, leaving its lowest, 8-ounce setting for the time he’s proven his comfort with a light trigger, or should the rifle end up in dad’s charge.

The rifle’s feature set rounds out with an interchangeable bolt handle for big or little hands, an easily manipulated and very smooth 90-degree bolt throw with excellent primary extraction, and a bayonet-style firing pin assembly for easy field stripping. The Origin and Ridgeback combo runs on easily sourced AI-pattern mags, and includes a pinned, 20-degree, 1913 optic rail.

Up Top

Big knobs make it easier for little hands to turn, and we wanted an uncluttered reticle with subtensions that match the dials. You do you, but our kid’s learning to use milliradians out of the gate. We figure there’s no chance mils are going away soon since they’ve been adopted by our nation’s military. There’s no point in saving weight since we’re building a recoil-absorbing machine. So, we figured we’d get the heaviest thing we could find in a competitive magnification range, namely something in the 5-25 neighborhood. The Vortex Razor HD Gen II 4.5-27 hit all the marks, and is a scope junior won’t outgrow … and neither will dad.

A few usability touches like a DOPE holder from Prater Precision and a magnification ring handle pay big dividends in reducing frustration for a new PRS shooter.

Bench time

Working at a slow, educational pace, father and son assembled the box of parts into a working rifle in an evening. The build matched up to our requirements for a rifle that could serve both sophomore and senior and, most importantly, could be had without waiting months on a gunsmith. All the parts were ordered off the shelf and arrived over the course of two weeks. There was no waiting on custom action options or barrel chambering that’ll backlog a parts order by months.

These bolt action parts came together in an evening, with no gunsmithing or swearing.

We used a stout vise, a barrel-action wrench, a barrel nut wrench, a torque wrench, headspace gauges, and a few common hand tools to make this shooter. The cost of the specialized tools is justified by the money and time we’d be waiting on a gunsmith to barrel, or rebarrel a rifle. Plus those tools give us the ability to switch calibers in less time than it takes to get in touch with a gunsmith.

Range time

We ran MDT’s 223 Rem mags without a single misfeed in the roughly 600 .223 rounds we’ve put through the gun. The polymer mags are grippy, too, when hands are wet with rain or sweat, and that feel provides a bit of confidence to adolescent hands. The very first group from the .223 build stacked up a 0.29-inch group using 73 grain ammo, and things got better from there.

Match Time

With the rifle proofed out, our 13-year-old trainee took possession and tucked three training sessions under his belt before joining his dad at his first PRS club match. The standing, offhand stage gave him some trouble, and the farthest, 1,000-yard targets eluded him, but everything inside of 800 yards was game-on for him. By match-end, our new shooter outshot a handful of grown-ups with many more hours behind a gun, and he did so confidently and safely.

This same rifle was rebarreled in 6.5 Creedmoor a few months later for use by an adult shooting his first PRS-style match. Their zeroing range session produced .30-inch groups with Hornady’s American Gunner 140-grain ammo. Match ammo ain’t cheap, and the gun shot the AG stuff well enough, so our adult trainee ran with it and ended up posting a respectable 8th place finish out of 25 shooters in his first PRS competition.

Sum it Up

Firstly, we took a bunch of bolt action parts, all but two components made by the same manufacturer, and screwed them together with the assistance of a 13-year-old in a basement after dinner, making a rifle that shoots as well as anything we’ve gotten from a heralded custom shop. The group sizes listed in the performance chart gives you everything you need to shut down anyone coming at you with a barrel-nuts-can’t-be-as-accurate argument.

Secondly, we built a gun that’s nearly futureproof. The R700 isn’t going away, and neither is its massive catalog of aftermarket support. That means a gun built on something like a Bighorn Origin can start as one thing, say a bolt-action trainer for your son, and live a double life as a venison collector with an investment in the appropriate parts and 30 minutes of bench time at the beginning and end of each hunting season.

Granted, our build is not an inexpensive rifle, but you can start with more modestly priced componentry and invest what, where, and when it makes sense. Building a bolty this way means you’re building a rifle that can’t be outgrown.

BUILDSHEETS: PAST AND PRESENT

• Going OFFGRID
• A Different Kind of Thin Blue Line
• This folder is Mk18-ish
• Light and Bright
• The Coyote Crusher
• The Contractor Service Rifle
• The SnipAR Rifle
• Building out the .224 Valkyrie
• M16A4 OIF Edition
• Not Just AR's: SBR AK
• 5.45 AK: Starting with the Arsenal 104
• The Real Call of Duty Soulful Wanderer
• Hacksaw Special: Making short rifles even shorter.
• Softening the AR-10
• Sleeper Retro AR Clone
• Government Surplus
• Downsizing to a 9MM PCC
• KE-15: Fixed Stock, No Slop

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