Two of the most popular alternative AR-15 calibers on the market right now, both excel at hunting, both pack a punch, but what is right for you?
Both cartridges cover a lot of the same ground, but there are some key differences that should be noted.
Grendel shines as a hunting cartridge for the AR-15. Due to the heavier bullet and higher energy than 5.56 NATO, it makes for a great mid-sized game cartridge to around 350 yards.
Whitetail, mule deer, wild pigs, and more are all squarely in the size range of what Grendle is great for.
Recoil is mild, lethality is great, and follow-up shots are quick. In all, Grendel is an outstanding little cartridge for hunting with.
Long Range Precision Shooting
Grendel doesn’t get nearly as much credit as it should for a long range shooter. The fact is, for target shooting and with the right handload, Grendel has ballistics very close to that of .308 Winchester.
That might not be impressive compared to some of the fancy 6mm competition rounds in the field now, but for a little cartridge designed for the AR-15 that’s a lot.
Personally, I’ve taken 6.5 Grendel out past 800 yards and had a blast with it. Friends of mine have really pushed their Grendels to the limit though and commonly push their rifles to 1,200 yards.
If you’re looking for a rifle that can double as a hunting rifle and as a PRS gas rifle, Grendel makes a good argument for it.
I don’t really love the Grendel for home defense mostly because of over-penetration. The bullet is a little too heavy and moving a little too fast for my taste. But if you’re in a home where over-penetration isn’t a major concern for you, 6.5 Grendel offers a lot more punch over something like 5.56 NATO.
While you need a long barrel to really get the most out of Grendel, it also works very well with a short barrel. A 12.5” Grendel still pushes 123gr ammo at around 2,330 FPS -- that’s about the same as 7.62x39 Soviet from a 16” barrel.
At home defense ranges 123gr at 2,330 FPS is over 1450 ft. lbs of energy, compare that to a 55gr 5.56 NATO at 3,000 FPS at only 1,080 ft.lbs, Grendel packs a lot of punch.
A home defense 12.5” Grendel pistol or SBR makes for a great option. Throw a suppressor on it and you have a real contender.
I wouldn’t recommend using the normal steel-cased 123gr ball ammo for hunting, but if you get some stuff that is actually designed for the task then 7.62x39 makes for a great harvester.
While you’re limited on range to about 150 yards, 7.62x39 does the job well within that distance.
From small deer to large hogs, you can rely on 7.62x39 to be there to get the job done.
The nice thing also is that 7.62x39 suppresses really well, especially if you use subsonic ammo also. This limits your effective range a LOT more, but you can an ultra-quiet rifle that still puts meat in the freezer. Just make sure to check your local laws first.
Like I just mentioned, 7.62x39 is fantastic for shooting with a suppressor. Really, this was the inspiration for 300 Blackout and we know how popular that is now.
The huge upside to 7.62x39 over something like 300 BLK is that 7.62x39 is a lot cheaper. A LOT cheaper.
With big, heavy bullets and a good can, 7.62x39 throws a lot of weight around and does so without much noise at all.
Again, not my top pick for the job -- but 7.62x39 Soviet is a viable option. Another round that is good from a short barrel, this gives you basically the same bullet weight options as 6.5 Grendel but throws it at a slower speed.
This helps cut down on overpenetration but also cuts down on your energy too -- although it is still more than 5.56 NATO by a good 300 ft.lbs at least.
The short version is that from short barrels (10”-12”) Grendel and 7.62x39 are about even with 123gr ammo. But from standard or long barrels (16” to 22”) Grendel hits harder and goes further by a significant amount.
Normal Barrels (16”)
16” barrels are pretty standard these days but it’s also common to see Grendel barrels much longer especially if you’re planning to use it for hunting or long range.
That said, looking at 16” barrels to keep things even 6.5 Grendel throws a 123gr SST Hornady Black at about 2,480 FPS. 7.62x39 throws a 123gr SST Hornady Black at just 2,300.
Yes, literally the same weight bullet and the same barrel length -- 6.5 Grendel is sent moving almost 200 FPS faster.
6.5 Grendel also has an advantage in ballistic coefficient (how well the bullet moves through the air) and retains its speed for a longer distance.
Practically speaking, 6.5 Grendel 123gr SST will still have over 1,000 ft.lbf at 350 yards, 7.62x39 123gr SST will only have over 1,000 ft.lbf to about 225 yards.
Long Barrels (18”-24”)
Grendel also gets more out of extra barrel length, a 20” 6.5 Grendel will throw 123gr rounds at about 2,600 FPS… 7.62x39 with 123gr SST bullets only move at 2,350 FPS out of a 20” barrel.
Grendel gains 120 FPS out of 4 extra inches of barrel, 7.62x39 only gains a pitiful 50 FPS.
Short Barrels (10”-14”)
This is where things get a lot more even between the two and 7.62x39 can actually pull ahead in energy.
14” and under, 6.5 Grendel and 7.62x39 rounds are moving at about the same speed. 12” barrels of both shooting 123gr SST are almost perfectly even at 2,250 FPS and 2,270 FPS.
At those speeds, 7.62x39 technically hits harder -- 1,408 ft.lbf at the muzzle Vs. 6.5 Grendel’s 1,383 ft.lbf.
Now… are 25 ft.lbf going to matter when you’re already well over 1,000? No, not at all. There is nothing that 1,408 ft.lbf will stop or drop that 1,383 ft.lbf won’t.
But, for the sake of argument, 7.62x39 does win in short barrels.
Building Or Buying?
Both of these cartridges work well in the AR-15, although 6.5 Grendel does have some major advantages that we’ll talk about in a moment.
As far as special parts go, they take the same. To convert a normal AR-15 into one that fires either 7.62x39 or 6.5 Grendel you’ll need a new barrel, new bolt, and new magazines. But sadly, none of them are compatible with each other.
The good news is that this makes it easy to convert an old rifle of yours into a new cartridge!
Or you can go the easy route and just buy a new upper and some new magazines.
Personally, I like both options. If you have the tools and time, building a new upper or a new rifle is always a great experience.
But there is a dark side…
While 6.5 Grendel is very good in the AR-15, 7.62x39 Soviet has some drawbacks. The two biggest are the bolt and the magazines.
Because 7.62x39 is so much larger than 5.56 NATO, the bolt face has to be much larger. This leaves very little metal on the outside and can make for a bolt that is more likely to break. There are things manufacturers can do to help prevent this, and Bear Creek Arsenal uses a bolt specially designed for the task, but the facts are it is still a weaker bolt face than you might be used to.
Now, most people never have an issue with this, but if you go shooting flaming hot handloads or questionable gun show specials you bought off a guy wearing overalls and a bass pro trucker hat, you might run into some issues.
If you’re looking to make a 7.62x39 AR-15 as your SHTF rifle, I’d strongly recommend keeping a spare bolt in the grip or buttstock if you have the storage room.
For the magazines, because 7.62x39 has such a taper to it, this forces a magazine with a big curve. Since the AR-15 magwell is straight, this can cause some issues. This has mostly been solved by newer magazines, but make sure you don’t cheap out on this. Get quality magazines and get a couple of different brands to find what works best.
For you, I would say it just depends on what kind of range you want to get the most performance in.
If you need to reach out to 350ish yards, Grendel wins. But if you’re keeping it under 150 yards or so, 7.62x39 will save you some money on ammo prices.
[We'd like to extend a huge thank you to David Lane for his hard work on this article. Make sure to check out our 7.62x39 uppers and 7.62x39 rifles and 6.5 Grendel uppers and 6.5 Grendel rifles and leave a comment below with anything you've learned!]