.458 SOCOM and .450 Bushmaster, By the Numbers
The two cartridges answer the same question from different directions. .458 SOCOM was developed in 2000 by Marty ter Weeme of Teppo Jutsu, after a conversation with a special-operations veteran of Mogadishu about 5.56’s shortcomings, to put a heavy .458″ bullet in a standard AR-15 magazine from a short barrel; it is a proprietary cartridge with no SAAMI specification. .450 Bushmaster came from Tim LeGendre’s .45 Professional, licensed to Bushmaster and loaded by Hornady from 2007, as a SAAMI-standardized straight-wall (38,500 psi) that answers Jeff Cooper’s call for a big-bore “Thumper” carbine and, later, the straight-wall deer laws.
Both push a .45-caliber bullet with more energy at the muzzle than a .308: Hornady’s 250 gr FTX .450 Bushmaster at 2,200 fps makes 2,687 ft-lb; a 300 gr .458 SOCOM at 1,900 fps makes 2,405; Buffalo Bore’s 405 gr hard cast at 1,675 fps from a 16″ makes 2,523. The .458 also runs 500 gr subsonic loads at about 1,100 fps for suppressed use, which the .450, with its lighter bullets, does not do as well. Inside 150 yards either one is a hog and black bear cartridge; the .450 is the one that is legal in more straight-wall deer states, because it is a SAAMI cartridge with a listed case length.
Faxon builds all three barrels on the Gunner Big Bore contour: a straight .875″ body behind an .875″ × 1.9″ gas journal, carbine gas on the 16″ barrels and pistol gas on the 10.5″, and 11/16x24 threads. Twist is 1:16 on the .450 and 1:14 on the .458, which stabilizes the 500 gr subsonics. The .450 barrel carries an identification ring on the muzzle shoulder so the two are never confused. Both use the same .473″ case head, so one bolt, Faxon’s .458/.450, serves both, and both require the Big Bore upper.
Manufacturer-published factory data
| Cartridge | Load | Bullet | Muzzle velocity | Muzzle energy | Test barrel |
| .450 Bushmaster | Hornady BLACK | 250 gr FTX | 2,200 fps | 2,687 ft-lb | 20″ |
| .450 Bushmaster | Federal Fusion | 260 gr bonded SP | 2,200 fps | 2,794 ft-lb | not stated |
| .458 SOCOM | Underwood | 300 gr Ballistic Tip | 1,900 fps | 2,405 ft-lb | not stated |
| .458 SOCOM | Buffalo Bore | 405 gr hard cast | 1,675 fps | 2,523 ft-lb | 16″ |
| .458 SOCOM | Buffalo Bore Subsonic | 500 gr hard cast | 1,115 fps | — | 16″ |
Sources: Hornady, Federal, Underwood, and Buffalo Bore product pages. From the 16″ Faxon barrels expect the .450 figures at roughly 100 fps below Hornady’s 20″ number; the 10.5″ .458 gives up roughly 150–200 fps to a 16″ on supersonics and almost nothing on subsonics. Estimates, not Faxon chronograph figures.
Duty Series .458 SOCOM / .450 Bushmaster Barrels
All 1:14 / 1:16 twist, 4150 CMV, QPQ nitride inside and out, 11/16x24 muzzle. Weights are nominal; prices are MSRP.
What You Need to Build It
Faxon’s Big Bore upper receiver (required), Faxon’s .458/.450 bolt carrier group, a standard barrel nut, and magazines: standard 5.56 magazines single-stack both cartridges (a 30-round 5.56 magazine holds about 10), with .458 SOCOM- and .450-specific followers improving feeding. All three barrels take an .875″ gas block on a 1.9″ journal; the 16″ barrels a carbine-length gas tube and the 10.5″ a pistol-length tube. A heavy buffer is recommended. Muzzle is 11/16x24 with a .45-caliber bore, so only 11/16x24 big-bore devices or a .45-rated suppressor on an 11/16x24 mount fit.
What Every Duty Series Barrel Shares
Duty Series is Faxon’s 4150 CMV line: the M4/M16 barrel alloy, button rifled, stress relieved, and salt-bath QPQ nitrided inside the bore and out, which hardens the surface while adding virtually nothing to it, roughly a tenth the width of a human hair, and leaves no plated layer to wear through. Every barrel is turned, crowned at 11°, chambered, 100% wet magnetic-particle inspected, and nitrided, then has its gas port drilled and reamed and its extension torqued to 150 ft-lb, pinned, and headspaced with a go/no-go gauge, and is laser-engraved with the Faxon shield, order number, and cartridge and twist, in Faxon’s Greater Cincinnati, Ohio plant. Faxon’s AR-15 and AR-10 barrels have been voted Favorite Aftermarket Barrel by Shooting Sports Retailer every year since 2022. All Duty Series barrels › All rifle barrels ›
Duty Series .458 SOCOM / .450 Bushmaster FAQs
Why is the Big Bore upper required?
Because a standard AR-15 upper’s feed ramps and ejection port were cut for a .378″ case, and the .450 and .458 cases are .473″ at the head and much larger everywhere else. Faxon’s Big Bore upper opens the feed ramps and the ejection port for the fat case so it feeds and ejects reliably; on a standard upper the big bores can hang up on the ramps and short-stroke on ejection. Faxon requires it for every .450 Bushmaster and .458 SOCOM barrel.
.458 SOCOM or .450 Bushmaster?
The .450 is a SAAMI cartridge with a listed case length, so it is legal in more straight-wall deer states, and it shoots lighter, faster bullets flatter. The .458 runs heavier bullets, up to 500 gr, and does subsonic suppressed work the .450 cannot. For deer in a straight-wall state, the .450; for hogs, bear, and a suppressed thumper, the .458. Check your state’s rules before choosing.
What bolt do they use?
Both cartridges have a .473″ case head, the same as .308 Winchester, so both use Faxon’s .458/.450 bolt carrier group, which is an AR-15 carrier with a .473″ bolt face. A 5.56 bolt will not grip either case.
What muzzle devices fit?
11/16x24 devices with a .45-caliber bore, or a .45-rated suppressor on an 11/16x24 mount. No .30-cal or 5.56 device will pass the bullet. The .450 barrel has an identification ring on its muzzle shoulder to tell it from the .458 at a glance.
Ballistics are manufacturer-published figures from the test barrels stated; velocity estimates for other lengths are approximations, not Faxon chronograph data. Dimensions are from Faxon engineering prints; weights are nominal. Prices are MSRP. Check your state’s hunting regulations before choosing a cartridge.
