which one and why?

Only reason id go 7.62x39 is cheap ammo.

I assume you are asking about the Grendel? No contest. The Grendel wins that battle every time. The 7.62x39 had also had numerous feeding problems that I don't know if ever were ironed out to make it reliable.

6.5

I've been running a 7.62X39 on an AR platform for several years now, and for my application: hog extermination and venison collection at ranges of 150 yards or less, I couldn't ask for better performance. I feed mine a steady diet of hand loaded ammunition; as a matter of fact, it has never had a single round of factory fodder run through it. I recently added a "Slide Fire" stock to it to allow me to fire it in bursts. I have yet to have a single FTF or FTE.

I REALLY like my 6.5 Grendel. It has done me well out beyond 250 yards. With Hornady 123 gr. SST or Berger 130 gr. VLD-Hunting, it has been an outstanding performer.

With that said, I think a 6.8 SPC II might be a more convenient way to go with more options for rifles and for factory ammo. If you like to build and reload, then by all means, go with the Grendel.

The notion of feeding problems or reliability isn't an issue of the caliber, so much as of individual guns and the ammo being used. 7.62x39 is certainly a viable option, as are many calibers.

What it really comes down to is how you will be using it to hunt. Taking mikei's example, if you are only hunting shorter distances, either will work, but Grendel will cost you more. If you are hunting at further distances or plan to from time to time, go with the Grendel.

I love my 6.5 grendel, but as the poster said above the 6.8 SPC II might be the better solution--if you just want to buy a box of shells and go hunting. If you reload get the grendel..I'd leave the 7.62x39 alone...differ spec bores (.311 to .308) depending what you are shooting. Some cheap ammo is so dang dirty I would not shoot in my rifles...ect...just my 2 centavos...

I run the 7.62x39 for a hog gun. I put the cheap metal case ammo down the pipe and it is very accurrate. I put a longer firing pin in it and I have not had any problems with it.

looking for a good round for deer and hogs and good recoil gun that my 9 and 12 yr olds will have fun shooting 50-300 yards.

6.5

I don't know why you would limit to 7.62 x 39 vs 6.5 (assuming Grendel). The 6.8 SPC has become a popular choice also.

I have a 7.62 x 39. Never had a single issue with it. It has been very reliable. The only downside I have noticed is that it requires a bit more accuracy with shot placement. Just a tad shy on knockdown power. Otherwise, a joy to shoot.

As DNS stated above, the availability of over the counter ammo for the Grendel is limited. I imagine it would be fairly difficult to find on a small town shelf. Otherwise, the Grendel is an excellent choice.

The 6.8 SPC started out somewhat like the Grendel as concerns ammo availability, but because it has reached a certain level of popularity and growing, that issue has been overcome for the most part. I was running 3 thermal setups on .308. The .308 is probably my favorite hog round. It does an excellent job. However, if you spot and stalk it becomes heavy over the course of the night. It is also more difficult to stay in the scope on a running sounder due to increased recoil. So, I switched those setups to 6.8 SPC's. I did retain one thermal .308 and added one day scope setup in .308. The 6.8's are much lighter and I have been mostly pleased with the knockdown power. I have 3 6.8 thermal setups. They have all been very reliable to this point. The round is accurate and smooth shooting. I would urge a look see when considering the other 2 rounds.

Good luck on your search.

I've got a Hardened arms upper, have shot 100 rounds or so no problem. Of course it doesn't have that many rounds through it. The cheap ammo is hard to control a tight POI.

Everyone forgets or doesn't know you can have 6.5 Grendel ammo on the cheap as well. $5.95 for a box of 20 steel cased.

Ok, yeah most likely you have to order it online but it is another cheap alternative.

Love my Grendel!

I almost had myself talked into building a 6.5 Grendel with that ammo in mind. If I could have found a barrel/bolt combo at the price of a 7.62x39, that's the way I would have gone. That may be out there but I couldn't find it at the time and went with the x39. Mine is a Radical Firearms barrel and so far I have had not one hiccup with it. I "Mexican Matched" some steel cased ammo with 123 grain Hornady SP bullets and ended up with much better accuracy and terminal ballistics. It is fine for hogs and such. I scratch load brass cased for deer hunting and it is very accurate out of the 16" barrel. I have two 6.8 SPC rifles and may one day switch one to a 6.5 Grendel just for grins and chuckles.

First off I will say I'm a 6.5 nut! I have hunted for several years with the Grendel, from Wolf Gold ammo, hand loads, to Hornady ammo. Currently it has my night vision setup on it.
But this Sunday afternoon my new 7.62x39 dropped 2 boars with new Winchester brass, stuffed full with AA1680 topped with a Zombie max 123 grain bullet.
BUT if I go somewhere I don't know how far the shot will be: 6.5 Grendel, or my 6.5x284.

Another 7.62x39 hunter here; Mini-30, Savage 10FCM Scout, and Zastava Mini-Mauser. Been thinking about the new Howa Mini Action in black with the 20" barrel.

Howa mini action in grendal

7.63x39 Cheap ammo. It's what my AK & SKS shoot.

ended up getting a 6.8spc II

Congratulations!

I think you'll enjoy it. It's a quagmire with several good choices.

6.5G

30 Cal Choices for an AR:

7.62x39 or 300 Blackout

270 Choices for an AR:

6.8 SPC

6.5 Choices for an AR:

6.5 Grendel

All of these work, all have their good points and bad points.

I vote 7.62x39. I have no experience with the 6.5, but love me some x39

Good choice with mild recoil for the kiddos.

I to love my AR in 7.62 X 39 no issues with feed or ejector problems. I made the decision along time ago to only shoot brass, No steel casings.