rifle, ar-15, .308, 7.62mmI know that Armalite makes an AR-10 in .308. And I’m told that there are kits to convert an AR-15 to 7.62. It seems that the latter should be less expensive, but I wonder about the performance of adapting the lower power AR-15 to the higher power round. I could use some data from you all about the advantages and disadvantages of each. Or should I just invest in an AK? Is there a civilian clone of the M-110 out there?
Unless you want a bolt-action rifle, AR-15s can not be converted to 7.62mm/.308 if for no other reason than the magazine well is too small to accept a 7.62mm round. There exist bolt-action uppers for AR-15 lowers in calibers all the way up to .50 BMG. Other reasons include the recoil buffer being too light, the recoil buffer spring being too weak, and the lower being the wrong dimensions to accept any of the myriad uppers build to fire .308 from an AR-platform rifle.
The advantages of an AR in .308 (heretofore called the AR-10 platform for simplicity, even though the AR-10 is a specific Armalite model) are semi-auto capability in a harder-hitting round. It also maintains the same manual of arms as the AR-15/M4/M16/et al. platform, so training on the larger system is much more quick to pick up. The two platforms share many dimensions (trigger groups, pistol grip dimensions, rail/upper receiver height for mounting iron sights…) so aftermarket parts from the AR-15 are readily used on the AR-10.
Disadvantages are weight, size, and cost. The rifles are larger physically, heavier because of their increased size, and both the rifles themselves and the ammunition are more expensive. Another difference to be aware of is the magazine well and upper/lower dimensions. Armalite and DPMS have differing opinions on how this platform should be built, and have established two different patterns of gun. Most of the hard-use-gun makers (LaRue, LWRCi, LMT, Knight’s) have standardized around the pattern used by the Knight’s SR-25/M110 platform, but I can not remember which of the two the AR-25 is more similar to.
As a side note, the difference between 7.62mm and .308 is the opposite of the difference between 5.56mm and .223 — .308 is the more powerful of the two, and can fire both while 7.62mm chambers should not fire .308 rounds.
The AK-47 platform may be a 7.62mm round, but it’s apples-to-oranges to compare it with the 7.62mm NATO or .308 rounds. A better comparison for the AK-47’s round (7.62x39) would be the AK-74’s round (5.54x39), and in the AR platforms the AR-15 rounds 5.56x45 (5.56mm NATO) and 6.8x43 (6.8 SPC).
The M110 is a rifle built for the military by a company called Knight’s Armament. They sell a “civilian” version of it as the SR-25 Enhanced Match Rifle, which with modifications to the rail and buttstock was turned into the M110. Knight’s makes some extremely tough guns, built for some extremely hard use. If you’re looking for an AR-10 platform rifle they can’t be beat on quality and you get what you pay for.
Regarding the M-110, you don't have to settle for a 'clone'. You can buy an SR-25 from Knights Armament Company, the same company that makes the M-110 for the military. Other similar rifles include the LWRC R.E.P.R. and the LaRue OBR.
As for the Armalite AR-10, I have seen a student bring this rifle to a class and I am not very impressed with it. Despite the services of an armorer it malfunctioned constantly, finally going down hard with a trigger issue. The student ended up shooting most of the class with a borrowed AR-15.
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