| Aspect | Ar15 | Ar10 |
|---|---|---|
| Definition | Lightweight, magazine-fed, gas-operated rifle chambered in 5.56x45mm NATO. | Larger, heavier rifle platform chambered in 7.62x51mm NATO or .308 Winchester. |
| Purpose | Designed for close-quarters combat, sport shooting, and home defense applications. | Built for long-range precision, hunting large game, and designated marksman roles. |
| Core Mechanism | Uses direct impingement gas system with rotating bolt, standard since 1960s. | Employs direct impingement or short-stroke piston, depending on manufacturer variant. |
| Receiver Size | Features a smaller upper and lower receiver, non-interchangeable with AR10 parts. | Uses a longer, taller receiver to accommodate larger .308 cartridge dimensions. |
| Cartridge Length | 5.56x45mm cartridge measures 2.26 inches (57.4 mm) overall length. | 7.62x51mm cartridge measures 2.80 inches (71.1 mm) overall length. |
| Magazine Capacity | Standard magazines hold 30 rounds, with 10-round options for restricted states. | Typical magazines hold 20 rounds, with 10-round and 25-round variants available. |
| Weight | Complete rifle weighs approximately 6.5 to 7.5 pounds (2.9 to 3.4 kg) unloaded. | Complete rifle weighs approximately 8.5 to 10.5 pounds (3.9 to 4.8 kg) unloaded. |
| Barrel Length | Common barrel lengths range from 14.5 to 20 inches (37 to 51 cm). | Common barrel lengths range from 16 to 22 inches (41 to 56 cm). |
| Muzzle Velocity | Fires 55-grain M193 at about 3,250 feet per second (991 m/s). | Fires 147-grain M80 at about 2,800 feet per second (853 m/s). |
| Effective Range | Effective range is 500 to 600 meters for point targets. | Effective range extends to 800 meters for point targets. |
| Recoil Energy | Produces roughly 4 to 5 foot-pounds (5.4 to 6.8 J) of felt recoil. | Produces roughly 8 to 10 foot-pounds (10.8 to 13.6 J) of felt recoil. |
| Cost Per Round | 5.56x45mm ammunition costs approximately $0.40 to $0.60 per round. | .308 Winchester ammunition costs approximately $0.80 to $1.20 per round. |
| Magazine Price | AR15 magazines cost $10 to $15 for standard polymer 30-round models. | AR10 magazines cost $25 to $40 for standard metal 20-round models. |
| Parts Availability | Vast aftermarket support with thousands of manufacturers and interchangeable parts. | Moderate aftermarket support, but fewer standardized parts across different brands. |
| Recoil System | Uses a carbine or rifle-length buffer tube with standard spring and buffer. | Requires a heavier buffer and spring to manage increased bolt carrier mass. |
| Bolt Carrier Group | BCG length is about 6.5 inches (16.5 cm) and weighs approximately 0.9 pounds. | BCG length is about 8.5 inches (21.6 cm) and weighs approximately 1.5 pounds. |
| Gas Tube Length | Available in carbine, mid-length, and rifle lengths depending on barrel. | Typically uses rifle-length gas systems for smoother operation with larger cartridge. |
| Muzzle Thread | Standard muzzle thread is 1/2x28 inches for 5.56mm barrels. | Standard muzzle thread is 5/8x24 inches for .308 barrels. |
| Trigger Group | Uses a standard AR15 trigger with 5.5 to 7.5 pound pull weight. | Uses a compatible AR10 trigger, often with 4.5 to 6.5 pound pull weight. |
| Magazine Well | Magazine well is narrower, accepting only AR15-specific magazines. | Magazine well is wider, accepting only AR10-specific magazines. |
| Upper Receiver | Upper receiver has a flat-top Picatinny rail, compatible with most optics. | Upper receiver is longer and taller, with same Picatinny rail standard. |
| Lower Receiver | Lower receiver has a standard fire control group pocket and grip angle. | Lower receiver is larger, with a wider trigger guard and different takedown pin location. |
| Accuracy Potential | Achieves 1.5 to 3 MOA with quality ammunition and factory barrels. | Achieves 1 to 2 MOA with match ammunition and precision barrels. |
| Hunting Suitability | Suitable for varmints and small to medium game up to 150 pounds. | Suitable for medium to large game like deer, elk, and bear up to 500 pounds. |
| Legal Restrictions | Subject to state-specific bans on features like pistol grips and flash hiders. | Subject to same feature bans, but often classified as a "large-caliber rifle" separately. |
| Recoil Management | Requires less muzzle control; faster follow-up shots for multiple targets. | Requires more shooter strength and technique to maintain sight picture. |
| Barrel Profile | Offers government, pencil, and heavy profiles for different weight balances. | Offers mostly heavy or fluted profiles to manage heat and recoil. |
| Suppressor Compatibility | Works with 5.56mm suppressors, often with 1/2x28 direct-thread mounts. | Works with .30 caliber suppressors, often with 5/8x24 quick-attach mounts. |
| Historical Origin | Developed by Eugene Stoner in 1956 as AR-15 for Armalite. | Developed by Eugene Stoner in 1955 as AR-10 for Armalite. |
| Adoption | Adopted by U.S. military as M16 in 1963, widely used worldwide. | Adopted by several countries in small numbers, never standard U.S. issue. |
| Best-Fit Scenario | Ideal for tactical training, home defense, and budget-conscious shooters. | Best for long-range target shooting, hunting, and recoil-tolerant enthusiasts. |
Ar15 is a lightweight, magazine-fed, semi-automatic rifle platform. It fires the 5.56x45mm NATO cartridge from a detachable box magazine. It exists to provide accurate, low-recoil firepower for military, law enforcement, sporting, and defensive use.
Ar15 is a direct impingement or gas-piston operated, air-cooled, magazine-fed rifle design that uses a rotating bolt locking mechanism. It is chambered primarily for 5.56mm NATO rounds and features a modular upper and lower receiver configuration that allows rapid barrel and handguard changes.
| Characteristic | What It Means in Practice |
|---|---|
| Direct impingement | Gas from the fired round pushes the bolt carrier directly, keeping the system simple and light. |
| Modular receivers | Upper and lower halves separate, letting users swap barrels, calibers, and stocks quickly. |
| 5.56mm chamber | Uses standard NATO ammunition, offering flat trajectory and low recoil at typical engagement ranges. |
| Rotating bolt | Locks securely into the barrel extension, ensuring reliable extraction of spent cases. |
| Aluminum alloy frame | Weighs roughly 6.5 to 7.5 pounds empty, making it easy to carry for extended periods. |
| Buffer tube stock | Houses the recoil spring and allows adjustable length-of-pull for different shooter sizes. |
| Picatinny rail | Top rail accepts optics, iron sights, and night vision without permanent modification. |
| Magazine capacity | Standard detachable magazines hold 20 or 30 rounds, enabling rapid reloads. |
| Low recoil impulse | Recoil is mild, allowing faster follow-up shots and easier control for new shooters. |
| High customization | Thousands of aftermarket parts exist, so triggers, grips, and handguards fit almost any preference. |
| Advantages | Limitations |
|---|---|
| Lightweight design makes it easy to carry and maneuver in tight spaces. | Direct impingement system runs dirty, requiring regular cleaning to prevent malfunctions. |
| Low recoil allows shooters to stay on target for rapid follow-up shots. | 5.56mm round has less stopping power than larger calibers like .308 or .30-06. |
| Modularity enables users to change calibers, barrels, and stocks in minutes. | Buffer tube stock is not collapsible on fixed-stock models, limiting adjustability. |
| Massive aftermarket support means parts and accessories are widely available. | Gas system can be sensitive to underpowered ammunition, causing short-stroking. |
| Accuracy at 100-300 yards is excellent for most civilian and law enforcement tasks. | Barrel heats up quickly during sustained fire, degrading accuracy over long strings. |
| Ergonomic controls like the charging handle and safety are easy to reach. | Charging handle is located at the rear, which can be awkward for left-handed users. |
| Magazines are cheap, durable, and available in 10, 20, and 30-round capacities. | Rifle length gas systems can be picky about ammunition pressure variations. |
| Flat-shooting trajectory makes holdovers simple at typical hunting ranges. | Standard trigger pull is often heavy and gritty, needing an upgrade for precision work. |
| Parts interchangeability means a broken component can be replaced easily. | Aluminum receiver can dent or crack if dropped hard on a sharp surface. |
| Versatile platform works for competition, hunting, defense, and training. | Legal restrictions in some regions ban features like pistol grips or adjustable stocks. |
The Ar10 is a semi-automatic, gas-operated rifle chambered in 7.62x51mm NATO, designed by Eugene Stoner in the mid-1950s. It fires full-power cartridges with a rotating bolt and direct impingement system. It exists to provide a lightweight, accurate, and reliable platform for military and civilian long-range shooting, hunting, and competition.
The Ar10 is a selective-fire or semi-automatic rifle using a direct impingement gas system, a rotating bolt, and an aluminum receiver, designed to fire 7.62x51mm NATO or .308 Winchester ammunition. Its design features a multi-lug bolt head and a buffer spring housed in the stock extension. It is the larger-caliber predecessor to the Ar15 platform.
| Characteristic | What It Means in Practice |
|---|---|
| Caliber | Fires 7.62x51mm NATO or .308 Winchester, delivering roughly 2,600-2,800 ft-lbs of muzzle energy, about double the Ar15's 5.56mm. |
| Gas System | Uses a direct impingement system where propellant gas is tapped from the barrel to cycle the bolt, reducing moving parts and overall weight. |
| Receiver Size | Features a longer and taller upper and lower receiver than the Ar15 to accommodate the full-length 7.62mm cartridge, adding about 1.5 inches in length. |
| Magazine Capacity | Typically uses 10- or 20-round magazines, with standard AR-10 pattern mags interchangeable across many brands, though not with Ar15 mags. |
| Effective Range | Accurate to 800 meters with a 20-inch barrel, making it suitable for precision shooting and medium-range engagement beyond the Ar15's 500-meter practical limit. |
| Recoil Impulse | Produces moderate recoil of about 15-20 ft-lbs, roughly double the Ar15's 7-9 ft-lbs, requiring a stronger buffer and spring system. |
| Barrel Length | Common barrel lengths range from 16 to 22 inches, with longer barrels maximizing velocity and accuracy for the .308 round. |
| Weight | Weighs 7.5 to 10 pounds unloaded, significantly heavier than the Ar15's 5.5-7 pounds, due to the larger bolt, receiver, and barrel profile. |
| Bolt Design | Uses an 8-lug rotating bolt with a larger diameter and longer locking surface to handle the higher chamber pressure of 62,000 psi. |
| Compatibility | Parts are not interchangeable with Ar15, except for some grips and triggers, requiring dedicated Ar10-specific components for assembly. |
| Advantages | Limitations |
|---|---|
| Delivers significantly higher stopping power and terminal ballistics than the Ar15, making it effective for large game and long-range targets. | Weighs 2-3 pounds more than an Ar15, causing fatigue during extended carry or tactical use. |
| Maintains accuracy at distances beyond 600 meters, outperforming the Ar15's effective range by about 300 meters. | Produces higher recoil, which slows follow-up shots and requires more training to control effectively. |
| Uses a widely available and affordable .308 Winchester cartridge, with a vast selection of match, hunting, and surplus loads. | Magazines are heavier and hold fewer rounds (typically 20 vs. 30) than Ar15 magazines, reducing sustained fire capacity. |
| Offers a modular platform with interchangeable handguards, stocks, and triggers, allowing for custom builds tailored to specific tasks. | Parts and accessories cost 20-40% more than Ar15 equivalents due to lower production volume and larger material requirements. |
| Provides a longer barrel life of 5,000-10,000 rounds, compared to 3,000-5,000 for a 5.56mm barrel, due to lower pressure and slower erosion. | Requires a larger and longer receiver, making the rifle less compact and harder to maneuver in tight spaces like vehicles or doorways. |
| Features a robust bolt and receiver design that handles high-pressure cartridges reliably, with fewer malfunctions than smaller platforms. | Limited compatibility between manufacturers, as DPMS and Armalite patterns are not fully interchangeable, complicating upgrades. |
| Effective for hunting large game like deer, elk, and boar, where the Ar15's 5.56mm round is often considered underpowered. | Heavier ammunition reduces the number of rounds a shooter can carry, typically 200 rounds vs. 300 for 5.56mm at the same weight. |
| Can be configured with a 16-inch barrel for a compact carbine, still retaining effective power out to 400 meters. | Loudness and muzzle blast are greater than the Ar15, requiring hearing protection and muzzle devices to manage recoil. |
| Benefit from a large aftermarket for precision triggers, with two-stage options reducing pull weight to 2-3 pounds for accuracy. | Direct impingement system runs hotter and dirtier than piston designs, requiring more frequent cleaning to maintain reliability. |
| Offers a variety of barrel profiles from lightweight to heavy, enabling shooters to balance portability with sustained accuracy. | Initial cost is higher, with entry-level Ar10 rifles starting around $800, while comparable Ar15s cost $500-600. |
| Shared Aspect | How Ar15 and Ar10 Are Alike |
|---|---|
| Firearm Category | Both the Ar15 and Ar10 are semi-automatic, magazine-fed rifles designed for civilian sport and defense. |
| Operating System | The Ar15 and Ar10 both use a direct impingement gas system to cycle the action. |
| Receiver Design | Both the Ar15 and Ar10 split into an upper and lower receiver for cleaning and customization. |
| Material Construction | The Ar15 and Ar10 typically use aluminum alloy receivers with steel internal components. |
| Modular Platform | Both the Ar15 and Ar10 allow users to swap barrels, handguards, and stocks easily. |
| Trigger Mechanism | The Ar15 and Ar10 use a similar single-stage or two-stage trigger group design. |
| Safety Controls | Both the Ar15 and Ar10 feature a standard selector switch with safe and fire positions. |
| Magazine Release | The Ar15 and Ar10 use a paddle-style magazine release button located near the trigger guard. |
| Bolt Catch | Both the Ar15 and Ar10 include a bolt catch to hold the bolt open on the last round. |
| Charging Handle | The Ar15 and Ar10 both use a rear-mounted T-shaped charging handle for operation. |
| Picatinny Rail | Both the Ar15 and Ar10 feature a top rail for mounting optics and iron sights. |
| Aftermarket Support | The Ar15 and Ar10 have massive third-party markets for parts and accessories. |
| Disassembly Process | Both the Ar15 and Ar10 field-strip into two main receiver halves without tools. |
| Cleaning Routine | The Ar15 and Ar10 require regular lubrication of the bolt carrier group for reliable function. |
| User Skill Level | Both the Ar15 and Ar10 suit shooters with basic firearms knowledge and mechanical aptitude. |
| Training Workflow | The Ar15 and Ar10 use identical manual-of-arms drills for loading, firing, and clearing. |
| Accuracy Potential | Both the Ar15 and Ar10 can achieve sub-minute-of-angle accuracy with quality ammunition. |
| Muzzle Devices | The Ar15 and Ar10 accept threaded muzzle brakes, flash hiders, and suppressors. |
| Stock Options | Both the Ar15 and Ar10 support fixed, collapsible, and adjustable buttstock configurations. |
| Grip Ergonomics | The Ar15 and Ar10 share a similar pistol-grip angle for comfortable handling. |
| Legal Classification | Both the Ar15 and Ar10 are subject to the same federal and state firearm regulations. |
| Purchase Cost | The Ar15 and Ar10 have entry-level models priced similarly for budget-conscious buyers. |
| Resale Value | Both the Ar15 and Ar10 retain strong resale value due to consistent market demand. |
| Maintenance Parts | The Ar15 and Ar10 share common replacement springs, pins, and roll pins for repairs. |
| Reliability Standard | Both the Ar15 and Ar10 function reliably across a wide range of environmental conditions. |
| Recoil Management | The Ar15 and Ar10 both use an in-line buffer tube system to reduce felt recoil. |
| Competition Use | The Ar15 and Ar10 are both popular choices in practical shooting and marksmanship sports. |
| Home Defense | Both the Ar15 and Ar10 serve effectively as defensive carbines for civilian households. |
| Long-Term Durability | The Ar15 and Ar10 have service lives exceeding thousands of rounds with proper care. |
| Custom Builds | Both the Ar15 and Ar10 can be assembled from individual parts by experienced hobbyists. |
For most shooters, ammunition cost and recoil tolerance decide the winner. The Ar15 fires cheaper, lighter .223/5.56 rounds with mild recoil, while the Ar10 fires heavier, harder-hitting .308 rounds. If you want an affordable, versatile rifle for general use, choose the Ar15. If you need maximum long-range stopping power, choose the Ar10.
Choose Ar15 when you want a lighter rifle under 7 pounds for home defense, varmint hunting, or tactical training. It suits shooters on a budget because .223 ammunition costs roughly half the price of .308 rounds. The Ar15 also fits smaller-framed shooters better due to its shorter, slimmer stock and reduced recoil.
Choose Ar10 when you need reliable stopping power beyond 600 yards for big-game hunting like elk or deer. It excels for precision long-range shooting because the .308 round retains more energy and bucks wind better at distance. The Ar10 also suits reloaders who want larger case capacity for custom handloads.
| Common Myth | The Reality |
|---|---|
| "The AR in AR-15 stands for assault rifle." | The AR in AR-15 and AR-10 stands for ArmaLite, the original manufacturer, not assault rifle or automatic rifle. |
| "AR-15 and AR-10 use the same ammunition." | The AR-15 fires .223 Remington or 5.56 NATO; the AR-10 fires .308 Winchester or 7.62 NATO. |
| "AR-10 is just a bigger AR-15 with no real differences." | The AR-10 uses a larger bolt, receiver, and magazine; parts are not interchangeable with the AR-15. |
| "Both rifles have identical gas system lengths." | AR-15s commonly use carbine or mid-length gas systems; AR-10s use rifle-length systems due to longer receivers. |
| "AR-15 magazines will fit an AR-10 without modification." | AR-15 magazines are narrower and shorter; AR-10 magazines are wider and longer, so they are not cross-compatible. |
| "The AR-10 recoil feels the same as an AR-15." | The AR-10's .308 round produces significantly more recoil than the AR-15's 5.56 round. |
| "AR-10 barrels are the same diameter and length as AR-15 barrels." | AR-10 barrels are thicker and typically longer, with a larger bore diameter and different muzzle threads. |
| "Both rifles weigh the same when fully loaded." | A loaded AR-10 weighs 1.5 to 3 pounds more than a loaded AR-15 due to heavier barrel and receiver. |
| "AR-15 and AR-10 bolt carrier groups are interchangeable." | The AR-10 bolt carrier is longer and wider; the bolt face is larger, so they cannot be swapped. |
| "You can use AR-15 triggers in an AR-10 without issues." | AR-10 triggers have different pin sizes and geometry; AR-15 triggers may not fit or function reliably. |
| "The AR-10 is fully automatic by design." | The AR-10 is semi-automatic only; full-auto versions are restricted and not standard civilian models. |
| "AR-15 and AR-10 use the same buffer tube and spring." | AR-10s require a heavier buffer and stronger spring to handle the .308's recoil impulse. |
| "Both rifles have identical effective ranges." | The AR-15 is effective to 600 yards; the AR-10 reaches 800 to 1000 yards with .308 ammunition. |
| "AR-10 upper receivers fit on AR-15 lowers." | AR-10 uppers are taller and wider; they do not mate with AR-15 lowers due to different takedown pin locations. |
| "The AR-15 was designed before the AR-10." | The AR-10 was designed first in 1955; the AR-15 was a scaled-down version developed later in 1956. |
| "AR-10 handguards are identical to AR-15 handguards." | AR-10 handguards are longer and have a larger inner diameter to fit the thicker barrel and gas tube. |
| "Both rifles use the same muzzle devices." | AR-15s use 1/2x28 threads; AR-10s use 5/8x24 threads, so muzzle devices are not interchangeable. |
| "AR-10 accuracy is always worse than AR-15 accuracy." | AR-10s can match AR-15 accuracy; both are capable of sub-MOA groups with quality ammunition. |
| "The AR-10 is illegal in all states." | The AR-10 is legal in most states; only states with assault weapon bans restrict its sale or features. |
| "AR-15 and AR-10 have the same magazine capacity limits." | Magazine capacity limits are set by state law, not rifle type; both can use 10, 20, or 30-round magazines where legal. |
| "AR-10 parts kits are interchangeable with AR-15 parts kits." | Lower parts kits differ; AR-10 uses a larger bolt catch and different pivot pin, so kits are not universal. |
| "Both rifles have the same rate of fire." | Semi-auto rate is trigger-limited; but AR-15 cycles faster due to lighter bolt and lower recoil impulse. |
| "AR-10 ammunition is cheaper than AR-15 ammunition." | .308 Winchester costs about twice as much per round as 5.56 NATO, making AR-10 shooting more expensive. |
| "The AR-10 is just a hunting rifle, not a tactical rifle." | The AR-10 is used for hunting, competition, and tactical roles; it is versatile, not limited to one purpose. |
| "AR-15 and AR-10 use the same charging handle." | AR-10 charging handles are longer and wider; AR-15 handles may not engage the AR-10's bolt carrier properly. |
| "Both rifles have identical safety selector positions." | Both use the same safe-fire-semi layout, but AR-10 selectors may require a different detent spring. |
| "AR-10 barrels are always longer than AR-15 barrels." | AR-15 barrels range from 10.5 to 24 inches; AR-10 barrels range from 16 to 24 inches, so lengths overlap. |
| "The AR-15 is a civilian-only rifle with no military history." | The AR-15 was adopted as the M16 by the U.S. military in the 1960s; civilian versions are semi-auto only. |
| "AR-10 and AR-15 have the same gas tube diameter." | AR-10 gas tubes are slightly longer and have a larger diameter to match the longer receiver and bolt carrier. |
| "You can convert an AR-15 to an AR-10 with just a barrel swap." | Converting requires a new upper, bolt, magazine, and buffer; a simple barrel swap is not possible. |
Difference Between Ar15 and Ar10 comes down to caliber and receiver size: AR-15 fires .223/5.56 with a smaller upper; AR-10 fires .308/7.62 with a larger one. Choose AR-15 for lighter recoil and cheaper ammo. Choose AR-10 for long-range power and hunting larger game.
## FAQ ### What is the main difference between an AR-15 and an AR-10? The primary difference is the cartridge size: the AR-15 fires the smaller .223 Remington or 5.56 NATO round, while the AR-10 is chambered for the larger .308 Winchester or 7.62 NATO cartridge, which delivers significantly more power and range. ### Which rifle is better for long-range shooting, the AR-15 or the AR-10? The AR-10 is better for long-range shooting because its .308 round retains velocity and energy more effectively at distances beyond 600 yards, whereas the AR-15's .223 round drops faster and loses power past roughly 500 yards. ### Are AR-15 and AR-10 magazines interchangeable between the two rifles? No, AR-15 and AR-10 magazines are not interchangeable because the AR-10's larger .308 cartridge requires a wider magazine body, and the magazine release notch sits in a different position on the receiver, so each rifle needs its own dedicated magazines. ### What is the typical weight difference between an AR-15 and an AR-10? The AR-10 typically weighs 1.5 to 2.5 pounds more than a comparable AR-15, with a standard AR-15 weighing around 6.5 to 7.5 pounds empty while an AR-10 usually comes in at 8.5 to 10 pounds, due to the heavier barrel and bolt carrier group. ### Can I use AR-15 lower receiver parts on an AR-10 build? No, you cannot use AR-15 lower receiver parts on an AR-10 build because the AR-10's lower receiver is physically larger to accommodate the .308 magazine, and critical components like the trigger pins, bolt catch, and buffer spring are dimensionally different. ### Which rifle has less recoil, the AR-15 or the AR-10? The AR-15 has significantly less recoil because the .223 round produces roughly half the felt recoil of the .308, making the AR-15 easier to shoot accurately in rapid succession and more comfortable for new shooters or smaller-framed individuals. ### What is the effective range difference between the AR-15 and the AR-10? The AR-10 has a substantially longer effective range of about 800 to 1,000 yards with .308 ammunition, while the AR-15's practical effective range is limited to roughly 400 to 600 yards with .223 rounds, making the AR-10 the clear choice for distance shooting. ### Is the AR-10 more expensive to shoot than the AR-15? Yes, the AR-10 is noticeably more expensive to shoot because .308 Winchester ammunition typically costs 40 to 60 percent more per round than .223 Remington, and the AR-10 also consumes more powder and lead per shot, increasing both ammo and barrel wear costs. ### What is the most common mistake beginners make when choosing between an AR-15 and an AR-10? The most common mistake is buying an AR-10 for general-purpose or home-defense use without considering its extra weight, higher ammo cost, and stronger recoil, when the AR-15's lighter weight and lower cost make it far more practical for most beginners' needs. ### Can I switch my AR-15 upper receiver to an AR-10 upper receiver? No, you cannot switch an AR-15 upper to an AR-10 upper because the AR-10 upper receiver is longer and taller to fit the .308 bolt, and the pin locations, barrel nut threads, and feed ramp geometry are all different, so you need a complete separate rifle.