Skip to main content

Ruger AR-556 MPR Review

Ruger AR-556 MPR Review
Check Prices

Originally chambered in .22 caliber, the AR-­pattern rifle has seen widespread adaptation for a number of cartridges. Most are in the small-­ to- mid-­caliber chamberings, but there are a few big-­bore offerings in this once diminutive rifle.

The most popular big-­bore cartridge available in an AR-­15 is the .450 Bushmaster. It officially debuted in 2009, but its roots trace back to the wildcat .45 Professional developed by Tim LeGendre. He created the cartridge thanks in part to the “Thumper” concept espoused by Jeff Cooper. The goal was a cartridge capable of one-­shot kills on big game up to 250 yards.

//content.osgnetworks.tv/gunsandammo/content/photos/Ruger-556-MPR-1.jpg
//content.osgnetworks.tv/gunsandammo/content/photos/Ruger-556-MPR-2.jpg
The bolt in the AR-556 MPR .450 Bushmaster (far left) is made from a super­ alloy that is much harder to machine than traditional bolt materials. This compensates for the thin band of bolt material around the case compared to the bolt used for 5.56 NATO/.223.Rem. loads (near left).

While the .450 Bushmaster is no Johnny-­come-­lately, its popularity is greater now than when it was introduced. The rise in demand can be attributed to a series of state laws making the cartridge legal for hunting whitetail deer. For instance, in 2016, Michigan began allowing rifle hunting in its southern counties. To be legal, rifles had to be chambered for straight-walled .35-caliber or greater cartridges with case lengths between 1.16 and 1.8 inches, giving the .450 Bushmaster a huge spike in sales. At the forefront of all this demand was Sturm, Ruger & Co.

For many years, Ruger has made an effort to make the .450 Bushmaster accessible to all shooters. First came the low-­cost, bolt-­action American, then the Cooper-­inspired Scout and the timeless No. 1. Now Ruger is fielding the AR-­556 MPR in the hard-­hitting .450 Bushmaster.


//content.osgnetworks.tv/gunsandammo/content/photos/Ruger-556-MPR-3.jpg
The handguard free-floats the barrel for improved accuracy. It is also long enough to allow for good positional shooting.

Making It Work


Chambering an AR-­15 in such a large cartridge entails a lot more than just installing a bigger barrel and opening up the bolt face. The bolt face on an AR chambered in .223 measures a scant .378 inch. The bolt face on a .450 Bushmaster bolt measures .473 inch. Opening up a bolt face that much, while still making it fit in a .223-­sized barrel extension and receiver, leaves very little material around the case head when the cartridge is chambered.

The issue isn’t the pressure generated from firing the cartridge that causes the bolt head to rupture. Instead, thinning the amount of material around the case head reduces the amount of material holding the bolt lugs to the bolt body. Since there is a bit of residual chamber pressure when the bolt unlocks, binding force stresses the lugs and can lead to breakage. This is why Ruger spent a lot of time and resources choosing how they machine the .450 Bushmaster bolt, opting for a high-­strength superalloy.

A quality AR-­15 bolt is usually constructed from Carpenter 158 or 9310 steel. Carpenter 158 has been the preferred material since Eugene Stoner’s team selected it back in the late 1950s. Where 9310 offers a slight improvement over Carpenter 158, it’s still only appropriate for the smaller case heads, which leaves more bolt mass around the case head and additional material for bolt lugs.

//content.osgnetworks.tv/gunsandammo/content/photos/Ruger-556-MPR-4.jpg
The .450 Bushmaster is a low-pressure round. Even with a muzzlebrake, the blast is not abusive.

Ruger is very tight-­lipped about the composition of its super alloy, but one other manufacturer makes a similar product — the bolt alone sells for nearly $220. If you compare the price of the .450 Bushmaster to its 5.56mm counterpart, you’ll notice Ruger charges $200 more for the Bushmaster variant. This is due to the additional machining and material costs associated with manufacturing a bolt from this super alloy.


//content.osgnetworks.tv/gunsandammo/content/photos/Ruger-556-MPR-5.jpg
The .450 Bushmaster has a carbine-­length gas system and still has excellent bolt life because of the saami maximum 38,500 psi chamber pressure.

Given its nature, the mystery bolt material is very hard and dulls tooling quickly. However, it’s worth the price of admission to prevent a bolt lug from shearing at an inopportune moment. Ruger is currently the only manufacturer of a .450 Bushmaster AR that takes this highly inconvenient, but very important, manufacturing step, just to ensure the rifle doesn’t lose a lug.

This bolt should have no problem handling the 38,500 pounds per square inch (psi), which is the maximum SAAMI chamber pressure allowed for the .450 Bushmaster. (Most rifle cartridges have a max pressure between 55,000 and 64,000 psi.) The .450 Bushmaster’s low pressure is why the muzzle blast is relatively mild and why just about everyone who shoots one gets off the rifle and says, “That wasn’t so bad.”

//content.osgnetworks.tv/gunsandammo/content/photos/Ruger-556-MPR-6.jpg
The adjustable Magpul MOE SL stock is slim and features a steel sling swivel socket to make attaching and removing a sling easy.

The .450 Bushmaster is an excellent cartridge for hunting big game, but it is far from punishing. Guns & Ammo did all of its testing with polymer-­tipped jacketed bullets that are ideal for deer, elk and moose. Hard-­cast flat-­nose (FN) bullets are available from Buffalo Bore and would be a good choice for bear or other dangerous game out to 150 yards. Even with the tame muzzle velocity of 1,700 feet per second (fps), the 360-­grain bullet will still penetrate about 4 feet of bone and muscle. Think of the .450 Bushmaster as a lightly loaded .45-­70, but available in a handy little semiautomatic platform.


//content.osgnetworks.tv/gunsandammo/content/photos/Ruger-556-MPR-7.jpg
The Magpul MOE grip is a good choice for any AR. There is enough texture to grip well without having finger grooves that never seem to be in the right place.

Rifle Makeup

The AR-­556 MPR in .450 Bushmaster comes with a 15-­inch, free-­floating forend that surrounds an 18½-­inch barrel. A carbine-­length gas system is used on this rifle due to the low chamber pressure of the round. The long forend provides the shooter with plenty of real estate for his support hand in any positional shooting and lots of options when looking for field rests.

//content.osgnetworks.tv/gunsandammo/content/photos/Ruger-556-MPR-8.jpg
Ruger’s trigger is excellent. There is very little creep with a crisp let-off.

The barrel is hammer-­forged with 5R rifling and a 1:16-­inch twist with a corrosion-resistant nitride finish. Bottom line? This barrel should last forever. Hammer-­forged barrels have work-­hardened bores and, when combined with the low pressure from the .450 Bushmaster, throat erosion will occur very slowly. An owner would have to shoot thousands of dollars in ammunition through the barrel before it would wear out.

//content.osgnetworks.tv/gunsandammo/content/photos/Ruger-556-MPR-9.jpg
Each rifle ships with a five-round aluminum magazine.

The Magpul MOE SL stock and MOE pistol grip are quality parts that are not typically found on factory guns in this price range. Magpul does a lot of destructive testing on its line and builds its stocks and grips to take abuse. If you’re overly-­aggressive mortaring an AR to clear a stuck case, the buffer tube will likely deform before a polymer Magpul stock breaks.

//content.osgnetworks.tv/gunsandammo/content/photos/Ruger-556-MPR-10.jpg
The .450 Bushmaster has the same case head size as the .308 Winchester, but offers massive muzzle energy from the small and light AR-15.

Ruger manufactures its own trigger in this rifle called the Ruger Elite 452, a two-­stage model with a pull weight of about 4½ pounds. The trigger has a crisp let-­off and short overtravel. It is equally at home shooting tiny groups or rapidly dumping five rounds into whatever is trying to eat you.

Spending a day at the range with this rifle is not exactly pleasant, but it’s far from painful. Shooting steel all day isn’t going to be a popular pastime with the .450 Bushmaster, but walking through bear country with one would be far less troubling than without it. Every time the rifle fires, just over one ton of muzzle energy flies downrange. That will solve a lot of life’s problems when judiciously applied. Thanks to the detachable magazine, there can always be five rounds on tap.

Ruger AR-556 .450 Bushmaster

Check prices, read customer reviews or buy it at Everest

Check Prices

Current Magazine Cover

Enjoy articles like this?

Subscribe to the magazine.

Get access to everything Guns & Ammo has to offer.
Subscribe to the Magazine

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Recommended Articles

See More Recommendations

Popular Videos

Guns & Ammo TV: Shooting 1,270 Yards with the 5.56 NATO

Guns & Ammo TV: Shooting 1,270 Yards with the 5.56 NATO

Guns & Ammo Rifles & Optics Editor Tom Beckstrand was on location in Idaho where he pushed the limits of the 5.56 NATO cartridge in this segment of “Long Range Tech” for Guns & Ammo TV. Pairing a SIG Sauer MCX Virtus rifle loaded with Hornady's 73-grain ELD-M ammunition, Beckstrand attempted to ring steel set at 1,270 yards, an incredible distance for any 5.56-chambered rifle and beyond the typical range for an AR-15.

All About .300 Blackout

All About .300 Blackout

The .300 Blackout is here to stay, and we take some time to look at new technology surrounding this cartridge. Next, we pit subsonic rivals against each other before stretching the legs of this CQB round out to 600 yards from a short 9-inch barrel.

Guns & Ammo TV: Irons vs. Optics

Guns & Ammo TV: Irons vs. Optics

How much of an edge do optics give shooters? In this segment of Pros vs. Joes, Guns & Ammo TV puts Coordinating Producer Jeff Murray against Professional Shooter Chris Cerino.

Red vs. Green Lasers: Visibility in Bright Light

Red vs. Green Lasers: Visibility in Bright Light

In this segment of “At The Range,” Handgunning Editor Jeremy Stafford and contributor Patrick Sweeney compare the visibility of red and green lasers in outdoor, sunny conditions.

See More Popular Videos

Trending Articles

From milled slides to optics-included packages, these pistol options are all red-dot sight ready.14 Red Dot Ready Pistols You Must See Handguns

14 Red Dot Ready Pistols You Must See

James Tarr - December 20, 2018

From milled slides to optics-included packages, these pistol options are all red-dot sight...

Small, lightweight and purpose-built for sub-compact carry guns, Surefire's XSC pistol light takes on EDC illumination segment.Surefire XSC Micro-Compact Pistol Light: First Look Tactical

Surefire XSC Micro-Compact Pistol Light: First Look

Jeremy Stafford - September 10, 2020

Small, lightweight and purpose-built for sub-compact carry guns, Surefire's XSC pistol light...

The one glaring weakness in the .30-­caliber magnum cartridge lineup is best highlighted by examining the requirement around which Hornady designed the .300 PRC; the requirement came from the U.S. Special Operations Command (SOCOM). .300 PRC Review Rifle

.300 PRC Review

Tom Beckstrand - March 12, 2019

The one glaring weakness in the .30-­caliber magnum cartridge lineup is best highlighted by...

The Pulsar Thermion XG50 Thermal Riflescope is the first-ever riflescope to combine a BAE sensor, onboard recording, automatic & manual calibration options, multiple color palettes, and manual focus.Pulsar Thermion XG50 Thermal Riflescope - First Look Optics

Pulsar Thermion XG50 Thermal Riflescope - First Look

Guns & Ammo Staff - September 02, 2020

The Pulsar Thermion XG50 Thermal Riflescope is the first-ever riflescope to combine a BAE...

See More Trending Articles

More Rifles

The Savage Arms 110 Elite Precision is an excellent all-around rifle for most shooting activities that don't require light weight. It can be made to fit just about anyone, with a chassis that allows for accurate, rapid and effective positional shooting. And while the 110 Elite Precision is not inexpensive, it still costs less than most custom rifles. Savage Arms 110 Elite Precision Review: Excellent All-Around Rifle Reviews

Savage Arms 110 Elite Precision Review: Excellent All-Around Rifle

Proofhouse - September 15, 2020

The Savage Arms 110 Elite Precision is an excellent all-around rifle for most shooting...

The unique aspects of the magazine capacity, the ease with which it handles mirage and its extreme portability make the Desert Tech SRS A2 an excellent choice for anyone looking for a long-range precision rifle.Desert Tech SRS A2 Review Reviews

Desert Tech SRS A2 Review

Tom Beckstrand - July 27, 2020

The unique aspects of the magazine capacity, the ease with which it handles mirage and its...

The new Savage Rascal Minimalist mirrors the stylish lines and laminate stock of its bigger brother, the Minimalist, yet retains the features and compact sizing that has made the Rascal ideal for teaching kids marksmanship and safety skills.Savage Rascal Minimalist – First Look Rifles

Savage Rascal Minimalist – First Look

Guns & Ammo Staff - July 31, 2020

The new Savage Rascal Minimalist mirrors the stylish lines and laminate stock of its bigger...

Gun Tech Editor Richard Nance and Pro-Shooter Jim Tarr head to the range with both .177-caliber airguns to test their aim and demonstrate why the full-auto selector is often called the Air Gun Reviews: Full-Auto Fun Rifles

Air Gun Reviews: Full-Auto Fun

Guns & Ammo Staff - August 26, 2020

Gun Tech Editor Richard Nance and Pro-Shooter Jim Tarr head to the range with both...

See More Rifles

Magazine Cover

GET THE MAGAZINE Subscribe & Save

Digital Now Included!

SUBSCRIBE NOW

Give a Gift   |   Subscriber Services

PREVIEW THIS MONTH'S ISSUE Arrow

Buy Digital Single Issues

Don't miss an issue.
Buy single digital issue for your phone or tablet.

Buy Single Digital Issue on the Guns & Ammo App

Other Magazines

See All Other Magazines

Special Interest Magazines

See All Special Interest Magazines

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Phone Icon

Get Digital Access.

All Guns and Ammo subscribers now have digital access to their magazine content. This means you have the option to read your magazine on most popular phones and tablets.

To get started, click the link below to visit mymagnow.com and learn how to access your digital magazine.

Get Digital Access

Not a Subscriber?
Subscribe Now