450 Bushmaster vs 308: Big Bore AR-15 Hunting Cartridges

The 450 Bushmaster allows a deer hunter to convert their AR-15 carbine into a whitetail slaying machine simply by changing its bolt, barrel, and magazine follower.

But is it worth converting your AR-15 to the relatively new 450 Bushmaster – or would you be better served by sticking with the all-American hunting cartridge, the 308 Winchester?

In this article we analyze the differences between the 450 BM and the 308 Win so that you can make a more informed decision on your next hunting rifle cartridge.

What Is the Difference Between 450 Bushmaster and 308?

The 450 Bushmaster fires a 0.452” diameter bullet: almost 50% wider than the 308 Winchester’s 0.308” diameter bullet. Furthermore, the 308 has a bottleneck case, whereas the 450’s case is straight-walled.

Cartridge Specs

When evaluating centerfire cartridges, it’s good to begin by comparing their physical specifications. The 308’s bottleneck case doesn’t just look different from the 450’s straight-walled one. It also improves ballistic performance (as it prevents the tail of the bullet from occupying space that powder otherwise could have). The 450’s straight-walled case is an intentional compromise. Regulations in Michigan, Indiana, Illinois, Iowa, and Ohio all require the use of straight-walled cartridges for deer hunting.

Another major difference between 450 and 308 is bullet diameter. The 308 Win fires the tried-and-true 0.308” diameter bullet, whereas the 450 Bushmaster fires a wider (and less ballistically efficient) 0.452” bullet.

The 450 Bushmaster generally fires bullets weighing between 158 and 300 grains, with 250 and 260 grain loadings being most popular. In contrast, the 308 generally fires bullets weighing between 110 and 180 grains, with 150, 165 and 180 grain loads having the most fans.

The 308’s case length and overall length (OAL) are considerably longer than those of the 450. The 450 is stubby by design, as it was conceived to fit a standard AR-15 magazine (which allows a maximum overall length of 2.26”). Design of the 308 (2.8” OAL) predated formal designation of the STANAG magazine by almost 30 years.

Both rifle cartridges’ case capacities are nearly identical, though the 450 has slightly more (59.5gr H₂O) than the 308 (56.0gr H₂O).

The final major difference between the two rifle cartridges are their maximum pressures. SAAMI specifies that the 308 can handle 62,000 psi – whopping compared to 38,500 psi for the 450.

Straight-walled cartridges generally have lower chamber pressures. The 450 is no exception, though its pressure is still high relative to the AR-15 recoil system’s capabilities. The powerful 450 generates quite a fair bit of recoil, and exerts considerable bolt thrust against the recoil buffer and spring as a result. The 450’s pressure is just about the highest the AR-15 platform can accommodate before risking becoming damaged.

Recoil

The 308 and 450 are no slouches when it comes to recoil.

Free recoil energy is determined by four factors: firearm weight, powder charge weight, bullet weight, and muzzle velocity.

On average, 450 recoil measures approximately 24 ft-lbs; about one-fifth higher than the 308’s average of 20 ft-lbs. To put this into context, the 450 has just 3 ft-lbs less recoil energy than a 2-¾” 12 Gauge shotgun shell firing a 1 ounce slug.

That’s quite a lot of kick for an AR-15, though it can be mitigated with the use of a muzzle brake (or by making the firearm heavier).

The difference in recoil between the 450 and 308 isn’t too drastic, although the 308’s gentler kick does make it the better option for recoil-sensitive shooters.

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Muzzle Velocity and Kinetic Energy

The 308 reigns supreme when it comes to muzzle velocity and kinetic energy. This is largely due to its more efficient bottleneck design and higher pressure.

For this comparison, we will compare Hornady Superformance 308 165gr SST and Hornady Custom 450 250gr FTX ammunition.

The 308 bullet screams out of the barrel at a velocity of 2,840 fps, with 2,955 ft-lbs accompanying muzzle energy. Both facets of the 308’s muzzle performance outshine the 450 load’s 2,200 fps and 2,686 ft-lbs.

The 308 still outpaces the 450 when it is loaded with a heavier 178gr ELD-X bullet: 2,600 fps and 2,672 ft-lbs.

In terms of muzzle velocity and muzzle energy, the 308 clearly dominates.

Trajectory

Trajectory is how we quantify a bullet’s flight path as it travels downrange, measured in inches of bullet drop.

A flatter-shooting cartridge is preferable for long-range shooting, as it allows a shooter to make fewer adjustments compensating for gravity. A flatter trajectory also means a cartridge will be more forgiving of ranging mistakes.

There’s a reason why the 308 has been used for long-range shooting for over seven decades, and why you’ll never see the 450 at any F-Class competition firing lines. The 308 exhibits a considerably flatter trajectory compared to the 450 Bushmaster – especially at longer ranges.

To illustrate this, we will compare the same Hornady 308 165gr SST and 450 250gr FTX loads as we did in the previous section.

At 250 yards (which many consider the maximum effective range of the 450), the 250gr FTX exhibits -19” of bullet drop, plummeting compared to the 165gr SST’s -7” drop at the same distance, when zeroed at 100 yards.

This difference only becomes more dramatic at long range. At 400 yards, the 450 Bushmaster round has transitioned to subsonic and exhibited -80” drop, while the 308 has maintained supersonic velocity and only exhibited -29” drop.

The 308, which is designed for long-range shooting, dominates in terms of trajectory.

Ballistic Coefficient

Ballistic coefficient (BC) is a measure of how effectively a bullet resists wind drift and frontal air resistance. Put another way, it’s a numeric representation of how aerodynamic a bullet is. A high BC is preferred, as it indicates the bullet will buck the wind more capably and conserve more of its momentum downrange.

Heavy bullets generally have a higher BC. It takes more force to disrupt the flight of a heavier bullet than it does a lighter one. BC also varies from bullet to bullet depending on design, weight, and other factors that are beyond the scope of this article.

Although the 450 typically always fires a heavier bullet, the 308’s aerodynamic bullet designs grant it the higher BC by a wide margin.

The 308 has an average BC around 0.420, whereas the 450 Bushmaster has a BC closer to 0.200.

Picture a gun range where there’s a 10 mph crosswind. At 250 yards, the aforementioned 308 165gr SST exhibits 5” of wind drift; the 450 250gr FTX, 16”.

The 450 bullet may be heavier, but it is more easily blown off course as its wider cross-sectional area presents a larger target to wind.

Sectional Density

Sectional density (SD) is a measure of how efficiently a bullet penetrates its target. It is important to consider when hunting big and medium-sized game, as a bullet that can punch through thick hide, bone, and sinew is required.

SD is calculated via two variables: bullet weight and bullet diameter. The higher its SD, the deeper the bullet is inclined to penetrate. (Note that this is a simplified view of penetration. Other factors are also pertinent such as the bullet’s velocity on impact and capacity for terminal expansion.)

The 308’s dominance in ballistics continues, as its SD is higher than the 450’s. The 308 has an average SD of around 0.26: over 40% higher than the 450’s 0.18 SD.

The 308’s higher muzzle velocity focuses tremendous force into a smaller area, thereby causing its bullet to enter deeper into its target.

This is not to say that the 450 Bushmaster has inadequate penetration; only that the 308 bullet is inherently designed to penetrate body mass more effectively.

Hunting

The 450 Bushmaster is designed for hunting big game within 250 yards, and it does so extremely well.

Many would consider the 450’s effective range to be restrictive, though. It’s the result of its bullet’s inefficient design, which begins hemorrhaging velocity and momentum the instant it exits the barrel.

As shown in previous sections, the 308 is superior in every ballistic category. It has a longer effective range, maintains velocity and energy farther, resists wind drift more effectively, and penetrates deeper.

This begs the question: Is the 450 even needed as a hunting cartridge? And the answer is unequivocally “Yes!”

Many hunters are constrained by regulations requiring the use of straight-walled centerfire rifle cartridges during deer season. The 450 (and other straight-walled cartridges, such as 350 Legend and 50 Beowulf) offer such hunters a legal option for harvesting venison.

Although the 450 is ballistically inferior to the 308, it is an extremely powerful round within 250 yards: devastating on large game.

Furthermore, rifles chambered in 450 Bushmaster (picture an AR-15 with a 16–18” length) will be lighter and more maneuverable than an AR-10 chambered in 308. A pound or so might not make all that much difference when you’re benchrest shooting, but when you have to carry that rifle through the woods all day, any extra pounds add up quickly.

The 450 Bushmaster offers hunters a lightweight, compact hunting rifle option that packs a huge punch at short distances. High-quality factory ammo can produce MOA to sub-MOA levels of accuracy, making the 450 Bushmaster an excellent option for hunters who value precision.

If you plan on taking shots outside of 250 yards, you will need something more powerful, like a 308 (so long as it’s legal to use for hunting where you live).

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Ammo and Rifle Cost/Availability

The 308 Winchester is one of the most popular centerfire rounds in North America, bested only by the 223 Rem. Therefore, there are considerably more rifle and ammo options available for 308 compared to 450 Bushmaster.

Virtually every ammo manufacturer, like Federal, Remington, Barnes, Hornady, and Underwood, has multiple 308 options available to suit all of your hunting and long-range shooting needs. Furthermore, as the 308 is functionally identical to the military’s 7.62×51 NATO, you can find surplus ammo and brass relatively easily.

Buying in bulk is always smart. Make sure to check out our stock of bulk 308 ammo today!

On average, inexpensive FMJ practice ammo runs around $1/round, while premium hunting ammo starts at around $1.80/round.

Comparatively, 450 Bushmaster ammo is more expensive. Practice FMJ ammo starts at around $1.50/round, while hunting ammo goes for no less than $2.50/round.

You should have no issues sourcing 308 ammo, as it can be found in virtually every sporting goods store and gun store. You may find difficulty sourcing 450 Bushmaster ammo if you only shop locally, though.

As far as ammo variety is concerned, the 308’s massive popularity gives it about a 10:1 advantage.

In terms of rifles, the 308 is undoubtedly the more prolific option. There are bolt-action rifles galore from manufacturers like Marlin, Winchester, Remington, Savage, Sako, and Browning. Multiple semi-automatic options are also available, such as the M1A, FAL, AR-10, Kel-Tec RFB, and others.

Any AR-15 you have in your collection is a potential host for the 450. All that’s needed is a new bolt, barrel, and single-stack magazine follower.

There are other options available for the 450 , such as a Henry single-shot rifle, or the Ruger American Ranch or Savage 110 if you prefer a bolt action. Although these rifles would serve you well, they seem to be a bit of a disservice to a cartridge that was specifically designed for the semi-auto AR-15. That concern is moot if your state restricts hunting to bolt-action rifles, of course.

Neither cartridge is well suited for use in a lever-action rifle due to the types of bullets each fires (though you can find older Winchester lever-action rifles chambered in 308).

Reloading

If you enjoy rolling your own ammo, then the 308 Winchester and 450 Bushmaster are both right up your alley.

The 308 is a joy to reload in particular. A plethora of 0.308” diameter bullets are available to help you customize hunting or target ammo to your exact specifications. Tons of suitable powders for reloading 308 are also at your disposal.

The fact that the 450 is a straight-walled cartridge is a real blessing. Straight cases are easier to resize than bottleneck ones.

Plenty of .45 caliber bullets are available. Make sure to order the correct ones, though. For rifle bullets, .45 caliber is typically 0.458” (e.g. 458 SOCOM). A diameter of 0.454” is common for handgun rounds (e.g. 454 Casull). Both such bullets should be avoided, as the 450 requires 0.452” diameter bullets.

Exercise caution when reloading the 450, as excess pressure can cause problems with the AR-15 gas system. It is advisable to never exceed published maximum loads, as the 450 can be pressure-sensitive.

Also, if you use a roll crimp on a 450 round with a bullet cannelure, it is advisable to use a very minor crimp (thereby minimizing any additional pressure that could accompany a heavy crimp).

308 Winchester Ballistics

Note: This information comes from ammunition manufacturers. Actual ballistics obtained with your firearm can vary considerably from the advertised ballistics. Ballistics can vary from lot to lot with the same brand and type load.

A Brief History of 450 Bushmaster

The 450 Bushmaster was released in 2007 by Tim LeGendre of LeMAG Firearms, who based it around the “thumper concept” put forth by the late and great Lt. Col. Jeff Cooper. Cooper appreciated the utility and flexibility of the AR platform, but was unimpressed with the ballistic performance of the 5.56x45mm NATO (which is almost functionally identical to the 223 Rem).

Lt. Col. Cooper’s thumper concept was a new cartridge designed to: (A) be fired from the semi-auto AR-15, (B) have an effective range of around 250 yards, (C) be .44 caliber or larger, and (D) harvest large game with one shot. LeGendre was inspired by Lt. Col. Cooper’s concept and began development of a new round that met its specifications.

Dive into our expert breakdown and choose your next rifle upgrade with confidence!

Read more here: 450 Bushmaster vs 308

Source: https://freedombunker.com/2025/04/07/450-bushmaster-vs-308-big-bore-ar-15-hunting-cartridges/