What’s the Difference Between Armalite AR-10a and AR-10b Rifles?

The AR-10A family of ArmaLite® firearms is functionally identical to their AR-10B family. Operation, controls, and maintenance are the same. However, the AR-10A family is designed to accept early ArmaLite AR-10 “Waffle” magazines and good quality magazines copied from them, instead of ArmaLite’s proprietary steel magazines that are used in the AR-10B family of rifles.

Original ArmaLite AR-10 with Waffle Magazine
Original ArmaLite AR-10 with Waffle Magazine

Neither family of firearms will function correctly with the other family’s magazines. The AR-10B magazine is based on the magazine of the famed M-14 rifle. This magazine was adopted during the period of the “Assault Weapons Ban”, during which new Waffle magazines  couldn’t be legally produced. The AR-10B magazine has proven to be as supremely successful in the AR-10B as its predecessor was in the M-14, and ArmaLite will continue to offer it. Armalite has tested, recommends, and ships polymer Magpul 308 PMAG® 20LR magazines with their AR-10As. Other similar derivative magazines such as the KAC, M110, and DPMS / Remington 19 round magazines may fit and may function, but Armalite has not tested them so they can’t assess their reliability. You can purchase extra 308 PMAG®s from Brownells.

Magpul 308 PMAG
Magpul 308 PMAG

Physical differences between the “Waffle magazine and the M-14 style magazine necessitate differences in some components used in AR-10As as compared to similar components in the AR10Bs. Some components of our AR-10A firearms are unique to that family. For example, the AR-10A Bolt Stop, Magazine Catch, Upper Receiver, and Lower Receiver are not the same as those in our AR-10Bs. This Tech Note will explain the physical differences among those components.

ARMALITE GENERATION II AR-10B MAGAZINES

Earlier versions of ArmaLite’s AR-10B® magazines were adapted from M-14 magazines. Those magazines incorporated a plunger in the back of the follower that had to be manually pushed in to load the magazine. The new Generation II magazines feature an integral feature on the follower that allows the magazine to be loaded without need to hold in a plunger. In other words, the new magazine loads exactly like an M-16 magazine. In addition, the feed lips and follower were redesigned to significantly improve reliability of feeding.


AR-10A VERSUS AR-10B BOLT CATCHES

AR-10A VERSUS AR-10B BOLT CATCHES
AR-10A VERSUS AR-10B BOLT CATCHES

As you can see above, the AR-15 and AR-10A Bolt Catches are similar in shape.  However, the AR-10A Bolt Catches are clearly stamped AR-10A.  Additionally, if you look closely at the upper left portion of those two parts, you’ll see significant physical differences between the two. The AR-10B Bolt Catch is very different in shape than the other two.  Note the relatively large flat angled surface near the top of the AR-10B Bolt Catch


ARMALITE MAGAZINE CATCHES

Armalite Magazine Catches AR-10A VERSUS AR-10B
Armalite Magazine Catches AR-10A VERSUS AR-10B

Differences among the three Magazine Catches can be seen in the shape of the boss on the right end of each catch.   (This is the boss that engages the cutout in the magazine body in order to retain the magazine in the lower receiver.)

The M15 and AR-10B Magazine Catches are similar in design.  However, the magazine catch boss on the M15 Magazine Catch has a chamfer on its lower side (shown in red above), whereas the AR-10B boss lacks that chamfer.

The AR-10A Magazine Catch is easy to differentiate from the other two.  Note that the boss on the right end of the AR-10A Magazine Catch is rounded on its outer end.


ARMALITE AR-10 UPPER RECEIVER DIFFERENCES

ARMALITE UPPER RECEIVER DIFFERENCES AR-10A VERSUS AR-10B
ARMALITE UPPER RECEIVER DIFFERENCES AR-10A VERSUS AR-10B

The M15 Upper Receiver is obviously smaller than the two AR-10 Upper Receivers, so there should be no confusion with them.

The AR-10B and AR-10A Upper Receivers are easy to tell apart if you look at them from the bottom.  From the bottom, the two flats near the front of the AR-10B Upper Receiver are very obvious.  The AR-10A does not have those flats. The two divot cuts in the AR-10A Upper Receiver are less obvious, but clearly visible.


ARMALITE AR-10 LOWER RECEIVER DIFFERENCES

ARMALITE LOWER RECEIVER DIFFERENCES AR-10A VERSUS AR-10B
ARMALITE LOWER RECEIVER DIFFERENCES AR-10A VERSUS AR-10B

The AR-10A Lower Receiver has several obvious features that are not present on the AR-10B Lower Receiver (in addition to the “AR-10A” logo on the side of the AR-10A receiver).  Note the elevated surface on the AR-10A that comes downward from the front of the magazine catch cutout.  Also note the increased upward angle of the bottom of the magazine well on the AR-10A.   In addition, the shape of the boss around the takedown pin hole is changed on the AR-10A.

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