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Big Modern Sporting Rifles: The AR-15 and AR-10 may be ubiquitous but this platform can be made to handle much larger cartridges.

Well, they weren't going for curb appeal with these. That was my initial thought when first handling a truly big AR-type rifle. Having handled AR-15 and AR-10 rifles in military and civilian configurations for competitive shooting and other types of training, my first exposure to truly big ARs made them seem ungainly long. However, compared to large-to-Magnum cartridges, .223/5.56mm is downright diminutive.

Due to the AR-15's popularity, it seems everyone with a combo tool, torque wrench, vise blocks, and a bench vise is offering an AR-15 for sale. There are a small number of actual AR-15 "chip makers" (manufacturers making parts from scratch) and most of these AR-15 companies are assembling components sourced elsewhere. Eugene Ston-er's masterpiece--which is the longest serving service rifle in U.S. military history and the dominating platform for accuracy-intense Service Rifle and speed-oriented 3 Gun Rifle--is relatively straight forward to build. As gunsmiths building High Power rifles have put it, building a competitive National Match M14 is an exercise in the gunsmith's art and building a competitive National Match AR-15 is Erector Set assembly.

Since filing the original patent in 1956, Eugene Stoner's design has been copied in a near endless array of varieties and options, however, given that most sellers aren't actually making their own parts, most AR-15 companies are limited to assembling other company's components. Like Ford's Model T, you can have any option you want as long as it's .223/5.56mm; .308 if they offer an AR-10 variant. Most deviations from these chamberings are cartridges using .223 or .308 as the parent case. This keeps the bolt and action nearly identical with the only major change being the particular reamer used to cut chambers in the rifled blanks.

Here are some options if you're interested in something unique--and bigger--than what is commonly available in the AR-15 and AR-10 world.

Miller Precision by Acutech (406/892-4030, AcutechWorks. com) is a collaborative effort of Montana-based gunsmith Brandon Miller and Acutech. Located in Flathead Valley, Montana, Acutech is a 16,000 square foot manufacturing facility featuring a full-service CNC machine shop, precision CNC waterjet, laser, and plasma cutting shop, and a metal fabrication and sheet metal shop. This collaboration makes for efficient, precise manufacturing of complete firearms and their components--including barrels, suppressors, muzzle brakes and receivers--all under one roof. Miller received his degree in Gun-smithing Technologies from Murray State College and apprenticed under John Holliger of White Oak Armament. He specializes in long range precision rifles for military and law enforcement, competition, and hunting enthusiasts.

In addition to fitting standard length actions, the .300 Win. Mag. has proven quite effective for hunting very large game, and long range sniping and marksmanship. This round has become the most popular .30 caliber Magnum round to date, achieves its full ballistic performance in 24-26 inch barrels, maintains supersonic velocities beyond 1200 yards and is notably accurate. For a long time the .300 Win. Mag. was the king of long range competition. The cartridge still holds numerous long range competition records and remains competitive today.

.300 Winchester Magnum, purchased by the government as the Mk248, is a popular choice for sniping. The M24, its reconfigured M2010 variant, and the Mkl3 sniper rifles are available in this chambering. As the military now employs a self-loading sniper rifle in .308 guise, notably the MHO Semi-Au-tomatic Sniper System, a .300 Win. Mag. can also make sense and Miller Precision Arms has a good one in the Guardian. Weighing the same as the .308 MHO, the Guardian's more potent chambering greatly increases effective range.

Noreen Firearms

Peter Noreen founded Noreen Firearms (406/388-2200, and has been gun-smithing for nearly three decades, having made his mark custom-building dangerous game rifles based on scaled-up pre-'64 Model 70 Winchester actions. Mentorship of his son, Phil, began in the family-owned shop and covered rifle building from the ground up. Both father and son were keenly interested in ultra long range shooting (beyond 1,000 yards) which led to the development of their Ultra Long Range Rifle in 2007. Featuring a custom single-shot bolt action and collapsible stock of their own design, this 32 pound beast is triggered with an adjustable Timney unit and chambered in .50 BMG, .416 Barrett, .408 CheyTac and .338 Lapua. This would evolve into a self loader in 2010, the Bad News Ultra Long Range Semi-Automatic Rifle, an external piston driven, side-charged semiautomatic available in .338 Lapua, .338 Norma and .300 Winchester Magnum. The Bad News was the first AR-15 chambered in such large cartridges and has been praised in various tactical circles. The BN36 continued this trend, adapting a more standard stationary internal piston AR platform (sometimes referred to as "direct impingement") to standard length cartridges such as .30-06 Springfield, .270 Winchester, and 25-06 Remington. The company makes most of the components for its rifles inhouse, manufacturing the upper and lower receivers, making a muzzle brake of their own design, and turning the rifled blanks. About eighty percent of Noreen's employees are military veterans.

Maintenance and Setup

Anyone ever taught to handle an AR-15 will instantly be familiar with these big AR's manual of arms. The safety, trigger, take down pins, bolt catch, and magazine release works the same. Clearing and disassembly procedures are the same, the parts are just bigger. Cleaning is also the same. Avoid harsh cleaning treatment, specifically never use wire brushes or any type of abrasive, and stick with common solvents such as Hoppe's No. 9 and lubricants such as CLP (Cleaner, Lubricant Preservative.) Wipe everything down and keep the moving parts lubricated.

Pay attention with chamberings for cartridges that have been in service for a long time. For example, Noreen specifically advises against using any ammunition made before 1990, their reason being older ammunition can cause pressures above specifications and can cause damage. These sorts of differences in conjunction with the greater degree of gas pressure are one reason why big ARs often have user-adjustable gas blocks. Soldiers deploying to Iraq and Afghanistan through the mid-2000s and later were occasionally digging into World War II era ammunition reserves and feeding "Ma Deuce" with cartridges bearing headstamps from the 1940s. Given .30-06 is older still, it's possible to come across cartridges many decades old. There can be a break down of propellant in long term storage. Even slight moisture inside the case can cause corrosion, rendering the propellant into a gluelike substance and causing higher than normal pressure.

Gas Block Setups

Large AR rifles with an adjustable gas block need to be tuned to use properly. The main purpose of adjustable gas blocks is to allow adjusting the port pressure to the operating system, thereby fine-tuning the bolt velocity, which will result in a smoother shooting rifle. Additionally, the adjustable gas block is also useful in obtaining optimum port pressure on otherwise difficult-to-run setups, such as suppressed weapons, short-barreled weapons, or unusual chamberings for nonstandard cartridges. Most rifles cycle faster than necessary and the resulting "bolt slamming" effect is a noticeable part of the recoil impulse.

A new rifle or bolt assembly may have a great deal of friction between the gas rings and carrier and may require a break-in period during which the gas block must be run on a higher-than-normal setting until the gas rings wear into the bolt carrier. When new, the bolt is extremely stiff and may not cycle completely until broken in. Once the gas rings have worn in, re-adjust the gas block.

This is especially true with cartridges much more powerful than typical AR-15s and will likely see long rang performance ammunition with differing pressures at the gas port, which can cause a timing issue such as the bolt opening too fast, leaving the cartridge case swollen and attempting primary extraction too soon. This can leave pressure signs, such as marred brass, cra-tered or flattened primers, or ruptured cases.

Closing the gas port slows the gas flow and can ease harsh felt recoil, stove piping, or an the extractor tearing the case rim. On the other hand, if the bolt is not traveling far enough back to chamber the next round, there is not enough gas in the system and you will need to open the gas port up more. When new, the tight fitting parts may have more friction while breaking in and may require more gas as well. Typical tuning adjustments will be in quarter turn increments. Begin with the gas flow set to a minimal setting, load one round, and fire. If the bolt holds open, the gas block is set. If the bolt does not stay open, it is short-stroking and the valve should be opened about another 1/4 turn. Continue backing the gas adjustment screw out until the bolt holds open consistently on last round lock back. Changing ammunition can require an adjustment. Try the new load with the current setting and then adjusting accordingly. When the load and gas setting is finalized, non-permanent (blue) Loctite on the valve screw keeps it set. It is also possible to shut the valve completely if you want to cycle the rifle as a straight-pull bolt action.

Offering Big ARs

The BN36 Long Range variants were driven by the thought of recreating the Ml Garand and revamping it into an AR-style rifle. Given the desire for a longer, more powerful cartridge and AR-15 receivers limited to .223 size or variations, AR-10 is the next step up. However, even with larger bore wildcats, the AR-10 is still limited to ammunition that fits a short action, typically a maximum length of less than 2.8 inches.

Larger receivers expand this to full-length, even Magnum cartridges. For example, Noreen offers BN36 rifles based on their receivers chambered in .300 and 7mm Remington Magnum. Their Gen 2 "Bad News" rifles include a .338 Lapua chambering.

As a gunsmith offering custom work, one advantage is the higher potential price point. Noreen's cheapest BN36 offering is $1,749.99 and goes up from there. Contrast that to .223 AR-15s that are available from almost everyone with a bench vice, set of blocks, and a torque wrench. For a customer set on a self loader chambering something bigger than .308, there just aren't as many options and a gunsmith that can offer them is potentially a step ahead of the pack.

Also of advantage is that these parts tend to be made in the United States by quality builders. Both Miller/Acutech and Noreen are Montana-based companies. Noreen doesn't source any parts out and has made over 40,000 receivers for gunsmiths, all from 6061 and 7075 aluminum billet or forged receivers. Their "Bad News" line in .338 Lapua has become a signature rifle for Noreen Firearms.

The components are available for any gunsmith interested in tackling big ARs and adding it to their list of services. Beauty is in the eye of the beholder but measured performance is irrefutable. Big ARs can deliver performance and be a unique (and profitable) offering.

by Dean Meier
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Title Annotation:TECH TOPICS
Author:Meier, Dean
Publication:American Gunsmith
Date:Jul 1, 2018
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