These days, nearly any AR-pattern rifle chambered in .308 Winchester tends to get called an AR-10. It’s an understandable error; with AR-15 being a ubiquitous term for a genericized rifle produced by a hundred or more different factors, it’s easy to see how people could assume that AR-10 gets the same treatment.
But, the fact is that AR-10 is not a generic term, but a specific one. There isn’t really a universally-accepted generic term for AR-15-pattern rifles chambered in full-power rifle cartridges; they frequently get labeled as large-frame or large-pattern ARs, AR-308s, or a handful of other terms, but none have truly worked themselves into the firearm lexicon.
Instead, these full-powered semi-autos tend to get specific names, such as the two we will be examining here, the AR-10 and the LR-308. Despite both bearing a striking resemblance to an AR-15, they are different rifles, with different parts compatibility, aftermarket availability, and more.
Definition of an AR-10
There is only one line of rifles that can truly be called AR-10s, because the name is a trademark of Armalite, the original inventor of both the AR-10 and AR-15. The AR-15 design and associated trademarks were sold shortly after development, eventually leading to its commonality and the shared nature of the label.
AR-10, though, remains a property of Armalite, and so only Armalite rifles are true AR-10s, despite the name frequently being erroneously used to describe other AR-15-based .308 rifles.
The AR-10 was first developed by Armalite as a potential contender for the next U.S. service rifle. It ultimately was not selected and never entered service.
However, Eugene Stoner and the others at Armalite continued to refine the design, eventually creating a scaled-down iteration that fired a smaller, more manageable round: the AR-15. This innovation was partially spurred by the impact of the SKS and AK-47-style firearms in the theatre of war, where the lighter, lower-recoiling 7.62×39 was proving advantageous. A deeper comparison of these rounds can be found in our guide to tactical rifle cartridges.
The original AR-15 prototype would then go on to split in two, developing into the popular semi-automatic rifle that we know it as today and separately into the M16, and later, the M4 carbine.
AR-10s feature a distinct slant-cut receiver design utilized by only a few other large-frame AR manufacturers. They are available in two different types, Type A and Type B, each with their own unique attributes.
Definition of an LR-308
Similar to the AR-10, the LR-308 is a specific line of rifles manufactured by DPMS (Defense Procurement Manufacturing Services) Panther Arms. It is an AR-pattern rifle chambered in .308 Winchester, but is distinct from the AR-10 for several reasons, not just because of their different trademarks and manufacturers.
The largest difference between the AR-10 and the LR-308 is their receiver design. While Armalite uses its distinct slant-cut receiver, the LR-308 uses a more traditional rounded receiver, nearly identical to the design of the AR-15, but scaled up to handle full-power rifle rounds.
The LR-308 does not have any military pedigree; instead, it was a rifle developed by DPMS to meet the civilian need for a semi-auto rifle platform that fired a more capable round than .223 Remington or 5.56 NATO. The increased ballistic performance of the .308 Winchester combined with the rapid follow-up capability of the LR-308 made it popular for hunting, long-range precision, and more.
While the LR-308 was limited to its eponymous cartridge, modern DPMS-pattern rifles are chambered in all manner of large rifle cartridges, including the popular 6.5 Creedmoor. If you’re not sure which caliber is right for your next build, we recommend checking out our article on .6.5 Creedmoor vs .308 Winchester.
Compatibility between AR-10 and LR-308 Parts
Obviously, due to the difference in the receiver design, AR-10 and LR-308 upper and lower receivers cannot be mixed and matched. Nor can either receiver be paired with an AR-15 upper or lower, although some AR-15 and AR-10 parts are interchangeable.
The only way for the resulting rifle to function is if both the upper and lower receiver are the same pattern, whether AR-10, LR-308, or AR-15.
It’s worth noting that even within one rifle pattern, there can be variances. Armalite offers both Type A and Type B rifles, which have slightly different lower receivers. DPMS, for its part, offers high and low upper receivers, which have slightly different upper rail heights. As such, it is essential to verify that your parts are properly matched before assembling your rifle.
Even beyond this incompatibility, though, there are a number of components that must be matched specifically to one rifle or the other.
Barrel nuts, for example, are not interchangeable, but instead must be matched to the pattern of your upper receiver. AR-10 and LR-308 upper receivers have different thread patterns, making it impossible to use the other’s barrel nut successfully.
Gas tubes also have dimensional variations, with the AR-10 gas tube being slightly longer than the LR-308 tube. As such, an AR-10 tube in an LR-308 receiver would protrude too far into the receiver, whereas the inverse would not reach all the way to the gas block.
Lastly, it is essential that the bolt carrier group and barrel extension patterns be matched: i.e., use an Armalite BCG with an Armalite barrel, never a DMPS BCG with an Armalite barrel. The headspace dimensions of the two patterns are different, meaning that mixing them could result in a dangerous, though fireable, firearm at risk for catastrophic failure.
Most other parts, including charging handles, gas blocks, trigger components, detents and springs, etc., are interchangeable.
Which One is Right For You?
Both rifles are excellent performers from companies with long reputations for quality.
If you want a true AR-10, of course, then the Armalite is the clear choice. The “AR” part of “AR-10” quite literally stands for “Armalite Rifle,” and so they are really the only source for AR-10 rifles.
However, DPMS-pattern rifles have enjoyed a great deal of popularity in recent years, leading to a particularly robust aftermarket. Because the AR-10 pattern is proprietary to Armalite, very few third-party manufacturers build rifles or components around that design—which is part of what makes it so exclusive.
DPMS-pattern large-frame ARs, on the other hand, are offered by a variety of manufacturers, even if the LR-308 is solely a DPMS product. Because of this, the aftermarket of parts and accessories is somewhat more robust for DPMS-pattern rifles.
Additionally, because the DPMS pattern is more common, you may have an easier time finding accessories or components for a DPMS-pattern rifle, particularly if you plan to do the bulk of your shopping at brick-and-mortar stores rather than online.
In the end, either rifle will be perfectly capable of punching .30-caliber holes in your target, so it largely becomes a matter of personal preference.
Conclusion
AR-10 and LR-308 rifles are similar in a lot of respects. They can share the same grips, the same triggers, the same optics. They do largely the same job and perform it similarly. But beneath all that, they are ultimately different rifles and must be treated as such.
Receivers, gas tubes, barrel nuts, barrels, and bolt carrier groups must all be deliberately matched to build a functional rifle. Failure to do so can result in a rifle that is non-functional at best and dangerous at worst. As with all things firearms-related, care and caution must be shown when building an AR-10.
