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

Old 06-23-2022, 10:12 PM
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Default 450 Bushmaster vs 308: Big Bore AR-15 Hunting Cartridges

When it comes to hunting across the North American continent, bolt-action rifles are the go-to option. However, some hunters wanted to use their semi-auto AR platform rifles to hunt whitetail, hogs, and other medium to large sized game animals.

Sadly the 223 Remington is not an approved cartridge for deer hunting in most states and territories, but many shooters still wanted a semi-automatic hunting rifle that wouldn’t break the bank.

Enter the 450 Bushmaster, which allowed deer hunters to convert their AR-15 carbine into a whitetail slaying machine simply by changing its barrel, bolt, 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 will analyze the differences between the 450 and the 308 so that you can make a more informed decision on your next hunting rifle.

What is the difference between 450 Bushmaster and 308?

The major difference between the 450 Bushmaster and the 308 is that the 450 Bushmaster fires a 0.452” diameter bullet compared to 0.308” for the 308 Winchester. Furthermore, the 308 uses a bottle-necked case design while the 450 Bushmaster is a straight-walled cartridge.

Cartridge Specs

When evaluating centerfire cartridges, it’s a good idea to analyze the cartridge specs to gain more knowledge of each.

The biggest difference between the 450 Bushmaster and the 308 Win is the case design, as the 450 uses a straight-walled case compared to a bottle-necked case for the 308. Although the bottle-neck design is considered more efficient as it allows cartridges to have increased case capacity, they are not legal for deer hunting in some midwestern states. Hunting regulations in Iowa and Ohio as well as parts of southern Michigan and public land in Indiana require the uses of straight-walled cartridges.

The second major difference between 450 Bushmaster and 308 is the bullet diameter that each cartridge fires. The 308 Win fires the tried-and-true 0.308” diameter bullet while the 450 Bushmaster fires a 0.452” bullet.

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

The 308 case length and overall length is considerably longer than the 450 Bushmaster. This is primarily due to the requirement that the 450 fit into standard AR-15 magazines which allow for a maximum overall length of 2.26”. The 308 is not constricted by this requirement and has an overall length of 2.8”.

The case capacity of both rifle cartridges is nearly identical, though the 450 has slightly more capacity than the 308 with 59.5 gr and 56 gr, respectively.

The final major difference between the two rifle cartridges is the maximum pressure that each round can accommodate. SAAMI specifies that the 308 can handle a whopping 62,000 psi compared to 38,500 psi for the 450 Bushmaster. Straight-walled cartridges generally have lower pressure, but the 450 must maintain a lower chamber pressure due to the AR-15 recoil system. As the 450 Bushmaster is a powerful round and has quite a bit of recoil, there will be a considerable amount of bolt thrust exerted on the recoil buffer and spring. As such, if the round had any more pressure there is the potential that the rifle could be damaged.


Neither the 308 nor the 450 are a slouch when it comes to recoil.

Recoil is a combination of 3 primary factors: rifle weight, powder charge, and bullet weight. Both rifle cartridges can fire heavy bullets, however the 450 Bushmaster will generally fire heavier bullets.

Felt recoil will differ between shooters, stance, and rifle choice.

On average, the 450 Bushmaster recoil will measure approximately 24 ft-lbs compared to an average of 20 ft-lbs free recoil for 308. To put this into context, the 450 Bushmaster only has 3 ft-lbs less free recoil than a 2 ¾” 12-gauge shotgun shell firing 1 oz slugs.

That’s quite a lot of kick for an AR-15, though it can be mitigated with the use of a muzzle brake.

Although the difference between 450 Bushmaster vs 308 isn’t too drastic in terms of recoil, the 308 does have the lesser free recoil and is the better option for recoil sensitive shooters.

Muzzle Velocity and Kinetic Energy

The 308 reigns supreme when it comes to muzzle velocity and kinetic energy due primarily to its efficient design.

For this comparison, we will compare the Hornady 165 gr SST Superformance for 308 and the Hornady 250 gr FTX for 450 Bushmaster.

The 165 grain bullet for 308 comes screaming out of the barrel at 2,840 fps with 2,955 ft-lbs of energy compared to 2,200 fps and 2,686 ft-lbs for the 250 grain 450 Bushmaster. Even with a heavier bullet, such as the Hornady 178 gr ELD-X, the 308 still outpaces the 450 Bushmaster with 2,600 fps and 2,672 ft-lbs of force.

In terms of muzzle velocity and muzzle energy, the 308 clearly dominates for all factory loads.


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

Obviously, a flatter shooting cartridge is preferred for long-range shooting, as a shooter will require fewer adjustments to their optics to compensate for bullet drop. Having a flatter trajectory also means that a cartridge will be more forgiving of ranging mistakes.

There’s a reason why the 308 has been used for long range shooting for nearly 70 years and why you’ll not see the 450 Bushmaster on the firing line at any F-Class competitions. The 308 has a considerably flatter trajectory compared to the 450 Bushmaster at longer ranges.

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

At 250 yards, which many consider the maximum effective range of the 450 Bushmaster, the 250 grain bullet has experienced -19” of bullet drop compared to -7” for the 165 gr 308 load.

This difference only becomes more dramatic at long range. At 400 yards the 450 Bushmaster round has gone subsonic and experienced -80” of bullet drop while the 308 is still well above the speed of sound and has only experienced -29” of bullet drop.

As the 308 is designed for long range, it simply dominates in terms of trajectory.

Ballistic Coefficient

Ballistic coefficient (BC) is a measure of how well a bullet resists wind drift and air resistance. Put another way, it’s a numeric representation of how aerodynamic a bullet is. A high BC is preferred as this means the bullet will buck the wind easier.

Generally, heavy bullets will have a higher BC as it takes more force to disrupt the flight of a heavier bullet than a lighter one. Ballistic coefficient varies from bullet to bullet based on design, weight, and other factors that are beyond the scope of this article.

Although the 450 Bushmaster will typically always fire a heavier bullet than the 308 Win, the aerodynamic bullet designs utilized by the 308 give it the higher BC by a wide margin.

On average, the 308 will have an average BC around 0.42 while the 450 Bushmaster has a BC closer to 0.20.

To illustrate how bullet design plays a role in BC calculations, let’s consider a 10 mph crosswind with our 165 gr 308 round and 250 gr 450 Bushmaster. At 250 yards, the 308 has experienced 5” of wind drift compared to 16” for the 450 Bushmaster.

The 450 may be heavier, but as it presents a wider cross-sectional area to wind it is more easily pushed off course compared to the 308.

Sectional Density

Sectional Density (SD) is the measure of how well a bullet penetrates a target. This is extremely important when hunting big and medium sized game, as you need a bullet that can punch through thick hide, bone, and sinew.

Sectional density is calculated by comparing the bullet weight and the bullet diameter. The higher the SD the deeper the bullet will penetrate into the target. This is a simplified view of penetration as there are other factors to consider, such as bullet expansion and high velocity.

The 308’s dominance in ballistics continues as it has the higher sectional density compared to 450 Bushmaster.

On average, the 308 has a SD around 0.26 compared to 0.18 for 450 Bushmaster.

The 308’s higher muzzle velocity and energy focuses all that force into a smaller area, thereby penetrating deeper into the target.

This is not to say that the 450 Bushmaster has inadequate penetration, it’s just that the 308 will penetrate deeper by comparison.


The 450 Bushmaster was designed for big game hunting within 250 yards and it does this extremely well. However, the 450 is constricted to this effective range, as its inefficient bullet design hemorrhages velocity and energy quickly as it leaves the barrel.

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

And this begs the question, is the 450 Bushmaster even needed as a hunting cartridge? And the answer is unequivocally “Yes!”

Many hunters are constrained by hunting regulations that require the use of straight-walled cartridges for centerfire rifles. Otherwise, these hunters would be limited to the use of muzzleloaders or shotgun slugs.

The 450 Bushmaster, and other straight-walled cartridges like the 350 Legend and 50 Beowulf, offer hunters a legal option in their respective states for using their centerfire rifles for hunting.

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

Furthermore, rifles chambered in 450 Bushmaster, particularly an AR-15 with a 16-18” barrel length, will be lighter and more maneuverable than an AR-10 chambered in 308. A pound or so might not feel make all that much difference when you’re shooting at the range on sandbags, but when you have to carry that rifle all day in the woods through thick brush, those extra pounds add up quick!

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 in cartridge-restrictive states like Michigan, Indiana, Illinois, Iowa, and Ohio.

However, understanding the restrictions of the 450 Bushmaster is key to success when it comes deer hunting. If you plan on taking shots outside of 250 yards, you will need something more powerful like a 308.

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 a military caliber (7.62x51 NATO), you can find surplus ammo and brass relatively easily.

On average, inexpensive fmj practice ammo runs around $1/round while premium hunting ammo starts around $1.80/round and can go up from there depending on the manufacturer.

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

It’s also important to note that you should have virtually no issues sourcing 308 ammo, as it can be found in virtually every sporting goods store and gun store, whereas 450 Bushmaster might be a bit more difficult to source locally.

As far as ammo variety is concerned, the 308 has about a 10:1 advantage due to its massive popularity.

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

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

There are other options available for the 450 Bushmaster as well, such as a Henry single shot rifle or the Ruger American Ranch or Savage 110 if you prefer a bolt-action. Although these rifles will serve you well, they seem to be a bit of disservice to the cartridge as it was built for use in the semi-auto AR-15. However, if your state restricts hunting to bolt-action rifles, then these would be excellent options.

Neither cartridge is well suited for use in a lever-action rifle due to the bullets each fire, however you can find older Winchester lever-action rifles chambered in 308.


If you enjoy making your own hand loads, then both the 308 and 450 Bushmaster are right up your alley.

The 308 in particular is a joy to reload as there are a plethora of 0.308” diameter bullets available to customize your hunting or target ammo to your exact specifications. Furthermore, there are tons of powders available that are suitable for 308 reloading at your disposal.

When it comes to the 450 Bushmaster, the fact that it is a straight-walled cartridge is a real blessing as these are simpler to resize than bottlenecked cartridges.

There are plenty of bullets available in 45-caliber, however you need to ensure that you order the correct bullet size as there are some variations. For rifle bullets, 45-caliber is typically 0.458” in diameter for cartridges like the 458 SOCOM. Furthermore, 0.454” diameter is available for handgun rounds like the 454 Casull. These bullets should be avoided as 450 Bushmaster requires the 0.452” diameter bullets.

Care needs to be taken when reloading for the 450, as excess pressure can cause problems with the AR-15 gas system. Therefore, it is advisable to never exceed published maximum loads as the 450 can be pressure sensitive. In addition, if you are using a roll crimp on a 450 round with a bullet cannelure, it is advisable to use a very minor crimp to minimize any additional pressure that could accompany a heavy crimp.

A Brief History of 450 Bushmaster

The 450 Bushmaster was released in 2007 by Tim LeGendre of LeMAG Firearms based 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 (223 Rem).

His “Thumper concept” was a new cartridge designed to be fired from the semi-auto AR-15, had an effective range around 250 yards, was 44-caliber or larger, and could harvest large game with one shot. Tim LeGendre was inspired by Cooper’s concept and began development of a new round that met his specifications.

LeGendre used a .284 Winchester as the parent case for the design and dubbed the new cartridge the 45 Professional. The design was then licensed to Bushmaster who then collaborated with Hornady to manufacture ammo for the new concept.

Hornady requested that the case be shortened slightly to accommodate their 250 SST bullet. This change was accepted by Bushmaster and LeGendre, thusly the cartridge was renamed the 450 Bushmaster (450 BM for short) and released in 2007.

The 450 Bushmaster is one of the most successful Thumper rounds, followed closely by the 458 SOCOM and 50 Beowulf, boasting the most factory ammo options of the 3 rounds. Its bone shattering 2,200 fps and 2,700 ft-lbs of energy is extremely popular with feral hog and deer hunters for its impressive terminal ballistics and semi-automatic capabilities.

Dedicated 450 Bushmaster AR uppers are currently available but converting your AR-15 to 450 Bushmaster only requires a new barrel, bolt, and single-stacked magazine follower for your standard 5.56 NATO magazines.

Although the 450 Bushmaster is still a relatively new cartridge on the market, it is quickly gaining ground as one of the most popular Thumper Rounds available today.

A Brief History of 308 Winchester

The development of the 308 Winchester (military designation - 7.62x51mm NATO) began after the Korean War to replace the long-serving 30-06 Springfield round.

In 1954, the military officially adopted the 7.62x51mm NATO as their new cartridge and it saw limited service in Vietnam before being replaced by the 5.56x45mm NATO (223 Rem).

Winchester quickly saw the utility of the 7.62x51mm NATO round on the civilian market and introduced the new rifle cartridge as the 308 Winchester in its short action Model 70 rifle in 1952, two full years before the U.S. Military formally adopted the cartridge.

The 308 Winchester was almost an immediate commercial success for its astounding accuracy, stopping power, and an effective range out to 1,000 yards (with appropriate loadings). Since the 1950’s and even up to this day, the 308 Win has been a staple in deer hunting camps and in marksmanship competitions across the globe.

One of the appeals of the 308 Winchester for big game hunting is its versatility in bullet weight, typically ranging between 120 to 180 grains.

Although the 6.5 Creedmoor and the 300 Win Mag are becoming more popular in the hunting and precision shooting circles, there is no shortage of shooters who swear by and will never let go of their beloved 308 Winchester.

To read more about the 308 Winchester, check out the full history of the cartridge on our 308 Winchester history page.

If you’d like to learn more about how the 308 compares to other calibers, check out these articles below:
Final Shots: 450 Bushmaster vs 308

By virtually every ballistic category, the 308 Winchester is superior to the 450 Bushmaster on all accounts. The 308 has a longer effective range, lower felt recoil, better penetration, and flatter trajectory.

However, the 450 Bushmaster occupies a special hunting niche that can only be filled by a few other cartridges. As a straight-walled cartridge, the 450 Bushmaster allows hunters in states like Ohio and Michigan to use centerfire rifle cartridges for deer and large game hunting who would otherwise be restricted to using muzzleloaders.

The 450 also was designed with the AR-15 rifle platform in mind, which is lighter and less expensive than the heavier AR-10 rifle that is used for the 308.

And there is one intangible aspect that goes along with the 450 Bushmaster…Fun!

There’s nothing like plinking away with a thumper round like this. The recoil, the muzzle blast, the semi-auto capability just adds a level of fun and enjoyment that cannot be calculated on a ballistics table.

Sure, the 308 might be more efficient and technically better than the 450 Bushmaster, but there’s a coolness factor to the 450 round that cannot be quantified or rationalized. So, if you want a 450 Bushmaster, then go get yourself one regardless of whether your state or province requires such a cartridge for hunting or not.

As that’s the beauty of the 2nd Amendment, sometimes which cartridge is “best” doesn’t matter as much as which one YOU enjoy the most!

Continue reading 450 Bushmaster vs 308: Big Bore AR-15 Hunting Cartridges on for 308 ballistic data!
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