When you’re looking for a bigger WHUMP, Ruger’s straight-wall cartridge AR might be your poison

by Dr. Martin D. Topper

In the days before smokeless gunpowder, caliber selection was rather simple. Bigger and more dangerous game required larger bullets. But when smokeless powder became available, small and medium-bore high-velocity cartridges gained a solid following and today they dominate the hunting fields.

Then sometime in the 1990s, Jeff Cooper began calling for a bigger-bore “thumper” cartridge that would allow hunters to use an AR- type rifle to effectively take big game with a single shot at distances out to 250 yards. Tim LeGendre of LeMag Firearms took up Cooper’s challenge and produced the .45 Professional cartridge, which, after some tweaking in consultation with the ballisticians at Hornady, became the .450 Bushmaster. Sales of the .450 Bushmaster started rather slowly yet have since gained a steady following among those who hunt in states that only allow straight-walled cartridges when hunting with rifles.

This 150+ pound sow went down quickly after being hit with a single Remington Accutip in .450 Bushmaster.

More than ten companies have produced rifles chambered in .450 Bushmaster over the last 15 years, and about the same number of companies produce .450 Bushmaster ammunition with various bullet weights and styles today. The .450 Bushmaster remains popular despite competition in the last couple of years from Winchester’s .350 Legend, which fires a smaller .35 caliber bullet and produces less recoil. Unfortunately, the .350 Legend also produces significantly less muzzle energy and its smaller-caliber bullets do not have the wounding potential of the .450 Bushmaster’s larger projectiles. Given this, the .350 Legend may be a good cartridge for hunting game the size of smaller whitetails, but the .450 is more versatile when it comes to hunting larger black bears, wild hogs, and elk out to 100 yds.

When I moved to the South over 15 years ago, I learned that hunting whitetails could be a lot more expensive here than hunting hogs. At first, I used guns chambered in .223, .300 BLK, and .308 Win. on hogs. Unfortunately, I was in for a real surprise when I shot a 427 lb. boar at 50 yards. The bullet went through both lungs and its larger vessels, but the boar simply turned and ran. Fortunately, I was using an AR-type rifle and placed another shot into the same area. Even so, he kept on going and didn’t stop until he ran into a tree and knocked himself out! Clearly, I needed more power than I could get even from a .308 if I didn’t want to track a big, wounded hog in thick cover. I later acquired a Ruger M77 Scout rifle in .450 Bushmaster, and it proved quite effective against hogs in the 150-200 lb. range. They went down fast after being hit with a single shot. That convinced me that the .450 Bushmaster was generally superior to smaller cartridges for hunting hogs.

These four rounds clearly show the range of weights and different projectile designs that are available in .450 Bushmaster. From left to right they are: Underwood’s 220-gr. FTM Extreme Hunter, Hornady’s 250-gr. FTX, Remington’s 260-gr. Premier Accutip, and Federal’s 300-gr. JHP.

On the other hand, when I chronographed a couple of loads through the Scout’s short 16.1-inch barrel, I found that this short barrel wasn’t producing all the performance I expected from the .450 cartridge. I then traded the Scout for a Ruger AR-556 MPR, which has an 18.63-inch barrel. The muzzle velocity of the 250-gr. Hornady FTX load increased from 2162 fps to 2249 fps when fired from the MPR. This higher velocity delivered 2807 ft-lbs of muzzle energy—a gain of 213 over the 16.1-inch barrel. Switching to Remington’s 260 gr. Premier Accutip load, the velocity increased from 2075 fps to 2160 fps and muzzle energy increased from 2485 ft-lbs to 2693. This makes me wonder how much more performance I might get out of the Ruger American Rifle’s 22-inch barrel when chambered in .450 Bushmaster.

The author checks his zero using an MTM K-Zone shooting rest. The Ruger AR-556 MPR’s muzzle brake makes recoil quite controllable.

I recently took my Ruger AR-556 MPR out to the Flagler Gun Club and bench-tested it on their 65-yard range. I particularly like this distance because it represents the maximum distance for most of my shots at hogs. I used four different loads, representing the range of .450 Bushmaster ammo on the market. These included Underwood’s 220-gr. FTM, Hornady’s 250-gr. FTX, Remington’s 260-gr. Premier Accutip, and Federal’s 300-gr. JHP.

The first three loads all produced between 2693 and 2807 ft-lbs of energy at the muzzle. The .300-grain .45 cal. Federal load only generated 2422 ft-lbs, making this bullet weight appear to be too heavy for the powder capacity of the .450 Bushmaster case with currently available powders.

This .837-inch, three-shot group was fired at 65 yards using Underwood’s Fluid Transfer Monolithic (FTM) load with an all-copper Leheigh Defense bullet.

In addition, the Ruger AR-556 MPR’s rate of twist is 1:16, which is ideal for bullets between 170-260 grains, and this showed up in the accuracy tests. Group size at 65 yards was .837 inches for the Underwood FTM, .955 for the Remington Accutip, 1.158 for Hornady FTX, and 2.325 for the Federal JHP—again indicating that the Federal load’s bullet was too heavy for this particular rifle.

Finally, I shot a 12-inch plate at 200 yards with the Hornady and Remington loads, and easily rang steel with both guns.


The .450 Bushmaster is an excellent cartridge for hunting many species of big game out to 150-200 yards and it is especially effective within 100 yards. With an 18-inch or longer barrel, it overpowers a lot of other popular smaller-caliber cartridges, including the .350 Legend.

Primary Mission

The primary mission of the Ruger AR-556 MPR and its .450 Bushmaster cartridge is to cleanly take big game at close to moderate range in forested and semi-open areas.

What I Like

  • The power of the .450 Bushmaster cartridge, especially when fired in an 18- to 22-inch barrel.
  • The rapid follow-up shots provided by the semi-automatic operating system of the AR-556 MPR, even though you are not likely to need them.
  • The Ruger 452 AR Trigger in the AR-556 MPR is very precise.

What I’d Change

  • I’d prefer a 20-inch barrel on this rifle.
  • I’d like to see this rifle more available rather than being only sold in limited quantities online (as of this writing).

Compare To

With respect to hunting hogs, the .450 Bushmaster cartridge is a little better than the .338 Federal out to 150 yards, where the higher B.C. of the .338 bullet tips the scales toward the .338.

Ruger AR-556 MRP.450 Bushmaster Specifications

  • Firearm Type: AR-15 pattern rifle
  • Caliber: .450 Bushmaster
  • Action: semi-automatic
  • Trigger: Ruger 452 AR Trigger
  • Safety: Two-position thumb safety on lower receiver.
  • Barrel Length:63 inches
  • Rate of Twist: 1:16 RH twist
  • Overall Length:6-38.9 inches with telescoping stock
  • Overall Weight:4 lbs. unloaded
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