Everything You Need to Know About AR-10 Lowers

Everything You Need to Know About AR-10 Lowers
September 13, 2023 Edited June 4, 2024 1974 view(s)
Everything You Need to Know About AR-10 Lowers

Everyone knows that the AR-15 is one of the two most dominant firearm platforms on the planet and the most modular firearm system the world has ever seen. That one isn’t up for debate, nor is it particularly close. But did you know that the AR-10 actually came first? Of course you did; you’re a gun nerd, and you’ve been reading our blog, so we know you’re sharp. 

AR-10s are enjoying a well-deserved renaissance. With the modularity of an AR-15 (many parts are universal between the two), the hard-hitting .308 Winchester, and about half the price of an M1A, AR-10s are legitimate contenders. Let’s talk about the lower receivers specifically and everything you need to know about them. 


Does an AR-10 use a different lower?

One of the first questions asked is, “Does the AR-10 use a different lower?” Yes, the AR-10 definitely uses a different lower receiver than the AR-15. This is a fundamental difference between the two platforms. The .308 is a much longer case than the .223, meaning the lower receiver must be made to accommodate the additional case length. The AR-10 is a completely different design, although it looks basically the same. The magazines used in the AR-10 are also substantially larger, so there is no confusion about which goes where.  

 AR-10 lower side view on table

Do AR-15 and AR-10 use the same lower?

Again, they do not use the same lower receiver. The AR-10 is a unique lower which is capable of accepting the larger AR-10 magazines. Also, the upper receivers are different in that the holes for the takedown pins are farther apart.

This invaluable safety feature will keep you from accidentally installing the wrong upper on your lower. 


What lower does an AR-10 use?

The AR-10 uses a unique lower receiver designed specifically for the rigors of the larger and heavier .308. Of course, some things remain universal between the AR-15 and AR-10: modularity. The AR-10 is known for its application as a .308 rifle, but that is not the only caliber in which an AR-10 can be chambered. In fact, we suggest a couple of other fine calibers for this versatile rifle, including:

.22-250 for those long-range varmint hunts. 

6.5 Creedmoor, useful for medium game at long distances. 

.243 Winchester, a great option for young or small-statured shooters who want the reach of the .308 without the punishment or just a hot little round with a flat trajectory. 


.22-250, 6.5 Creedmoor, and .243 Winchester bullets side view on table comparison

Left to right - .22-250, 6.5 Creedmoor, and .243 Winchester


Of course, it goes without saying that you can own one single lower and really have four different rifles if you want an upper in each. Who are we to judge?


Can I use an AR-15 lower on AR-10 upper?

This is a HARD NO. 

The dimensions of an AR-15 lower are completely different than an AR-10 upper. Thankfully, the takedown pins are farther apart since the lower receiver is substantially larger and longer, so shooters who either don’t know the difference or aren’t paying close enough attention cannot accidentally mate the two. 

Here at Bear Creek Arsenal, we put safety above all other things, so please, if you are unsure how to assemble your AR-pattern rifle, research before you start slapping parts together. Building firearms has an inherent risk but is not dangerous when done correctly.  


What calibers can an AR-10 lower handle? 

.22-250, 6.5 Creedmoor, .243 Winchester, and .308 Winchester bullets comparison on table

Left to right - .22-250, 6.5 Creedmoor, .243 Winchester, and .308 Winchester


We touched on this a little earlier, but it bears repeating: the AR-10, like its little brother, is a multi-caliber platform. And we are here for it!

Four calibers are routinely used for the AR-10, all of which are fairly similar in cartridge length. The OG is the .308 Winchester, but there are others. The 6.5 Creedmoor has become both commonplace and quite popular for the AR-10 platform, combining the drop-dead precision of the 6.5 Creedmoor with the low recoil and rapid follow-up capability of the AR-10. 

The .243 Winchester is another great option, derived from the .308 case and necked down to a .24 caliber bullet. For young shooters and hunters, it is a great option. It has very little felt recoil in the AR-10 and shoots flatter than a pancake, and an AR-10 with a standard M4 stock and 16” barrel is quite compact.   


What’s better for deer, AR-15 or AR-10?

This question has way too many variables. There are calibers for the AR-15 that do quite well hunting deer (.350 Legend, .300 Blackout, 7.62x39mm, 6.5 Grendel), but they lack the range that the longer cartridges provide. An AR-15 in one of these calibers works great for the woods on Appalachia, but hunting those monster Whitetail in the Plains of Western Kansas or Nebraska? Consider the AR-10, where calibers are better suited for longer shots.


Is The AR-10 better than AR-15 for hunting?

Going back to the last paragraph, it’s hard to say which is “better.” It depends completely on what you are doing. The .300 Blackout has proven to be totally adequate at slaying medium game, especially deer and hogs. Several ammunition brands make deer-tailored ammunition in .300 BLK. But it is best for those shorter-range shots of ~100 yards or less. If you are in the woods, it’s a great pick. You can build a light AR-15 in .300 BLK or buy a complete rifle. But if you are out around Hardesty, Oklahoma, or Greensburg, Kansas, where trees are spaced approximately 2 ½ miles apart, an AR-10 makes sense. 


What is the most common AR-10 caliber?  

.308 Winchester bullet on table

The .308 Winchester still reigns supreme for AR-10s, which makes sense. It is the first and original caliber, and the .308 is wildly popular for all kinds of medium (and some large) game. 

The .308 is also one of the world's most popular precision target shooting calibers for high-power matches. Hence, it balances out to be an incredible all-around caliber for the venerable but highly effective AR-10.



The AR-10 is a great all-around performer for all kinds of tasks. It is an awesome medium-range hunter for all kinds of medium game (and even large with the right ammunition). A 20-round magazine and a red dot optic make it an effective dangerous game repellent. With the simple swap of an upper, you can transition to an effective competition rifle. Whatever you are looking for, the AR-10 can do it (even prairie dog hunts with our .22-250 rifles and uppers).


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John Evans
November 12, 2023
BCA has truly brought innovation to the shooting community. With every option available that may be wanted or needed, they have brought products to the working folk at a great price and quality, selection! With the AR8, AR10,and AR15 platforms, the sky is the limit. Thank you to everyone that works at BCA, your hard work is very important and appreciated.
January 24, 2024
Have a PSA AR10 lower, gonna be building a 18" 308 with it within the next few months! I really wish their was more standardization in the AR10 world, like their is with AR15s! Guess I'm just gonna have to buy a BCS AR10 IN 22-250, ,darn the luck!
Jerry Bassett
March 14, 2024
Thank you all for this information,there are a great number of new shooters that find this Ar15 and Ar10 configuration confusing this will help a good bit,I am happy with all my BCA purchases.
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