It seems a lot of people mix up the information on different cartridges. This is one of those times when the information is just wrong, and potentially very dangerous.
The 7.62×39 and .308 are completely incompatible. Every dimension of the cartridges is vastly different. The 7.62×39 is .55 inches shorter. Many people confuse the 7.62×39 with the 7.62×51. The 7.62×51 is safe to fire in a 308. The 7.62×39 is not.
What’s the difference Between the 7.62×39 and .308?
The 308 is the civilian version of the NATO 7.62×51. The 7.62×51 was adopted by the US military in 1951 and the civilian version, the .308, was introduced in 1952. It fires a .308 caliber (inches) bullet and has a maximum overall length of 2.67 inches.
The .308 is arguably the most common hunting rifle in the US, pushing out the old 30/30 and 30-06. It was developed to give 95 percent of the ballistics of the older 30-06 in a significantly smaller cartridge.
The 7.62×39 was developed by the Soviets in 1934 for the RPD machine gun. The round is most famous for its chambering in the many variants of the AK47, and for the SKS. All of them are Soviet developments.
It is by far the most popular cartridge in the world, being more common in northern and eastern Europe and in Asia than in the US. There really are no similarities between these two cartridges. Every specification is massively different, making the two incompatible.
Below is a chart of the specifications of the two rounds. This is in inches. Take a look.
Cartridge
| Cartridge | Bullet diameter | Neck diameter | Shoulder diameter | Base diameter | Rim diameter | Case length | Overall length |
| 7.62×51 NATO | .308 | .344 | .454 | .470 | .470 | 2.150 | 2.750 |
| 308 | .308 | .344 | .454 | .470 | .470 | 2.150 | 2.750 |
| 7.62×39 | .311 | .340 | .394 | .443 | .445 | 1.520 | 2.200 |
Just to be sure, I measured my own cartridges and got the same numbers. I added the 7.62×51 NATO for a reason. The question of shooting 7.62×39 in a 308 comes up often. I guess that people confuse the 7.62×39 with the 7.62×51 NATO. It’s my theory that that’s the confusion point for alot of people.
What will happen I fire .7.62×39 in a .308?
The shorter cartridge will fit in a 308 magazine, and may or may not feed into the chamber. I actually just loaded my .308 with 7.62×39 and attempted to cycle them through the action. It didn’t go very well. most of them wouldn’t go into the chamber unless I tilted the rifle on an angle.
If you do get it into the chamber, there is a very good chance that it won’t fire at all. The case won’t touch the bolt, where the firing pin is, and headspace at the same time. Headspace is when a part of the cartridge is pressed up against part of the chamber so the cartridge will not go any further forward. Since the Soviet cartridge is shorter, it will not headspace. It can rattle back and forth in the chamber.
If you load one in and pull the trigger, the firing pin will strike the primer and probably just push the cartridge forward since nothing will hold it in place. But if it were to go off, you have a serious problem. Normally, when a cartridge goes off as it’s supposed to, the case mouth expands to seal the gasses from going into the chamber. But if you shove a x39 in a 308, it won’t seal. But it’s still going to ignite the powder and propel the bullet.
How Dangerous is it to Fire 7.62×39 in a 308?
How dangerous is it to hold a hand grenade? That statement may seem extreme, but it’s spot on. The problem comes from two points. Number one, the cartridge will not headspace, it will not seal the expanding gasses from coming into the chamber towards you.
Number two, the 7.62×39 bullet is overly tight in a 308 barrel. That means that there will be more pressure in the chamber for longer while the tight bullet is pushed down the barrel. If the primer is struck by the firing pin and it goes off, the bullet will jump the half-inch gap and attempt to go into the barrel.
The case, not being supported by the larger chamber will rupture and the pressure from the exploding gunpowder will go into places not designed to hold pressure. If you are lucky, the bullet will exit the barrel and you will only have to deal with a massively stuck cartridge. If not, either the barrel or chamber will explode with massive force.
Will a 7.62×51 Fire in a 308?
Good news here! A 308 rifle is compatible with the 7.62×51 NATO cartridge. Even though the 308 was a later adaption of the 7.62×51 NATO, a 308 will safely fire a 7.62×51 NATO. The only real differences between the two are the case on the NATO round is thicker to work better in a belt_fed machinegun.
The thicker means it has less case capacity. If I take a 308 case and a 7.62×51 NATO case, they are identical in every dimension, except that the NATO cases are required to be thicker than the average 308. There really isn’t a requirement on the thickness of the civilian 308, but the US industry is more or less settled on a working standard.
What that difference in capacity means is that if you load identical volumes of the same gunpowder in both cases, top them off with the same bullet, and seat them to the same depth, the NATO will have more pressure. But that is only a concern when reloading a 308 from 7.62×51 NATO brass
The specifications for the NATO round are to be loaded a bit lighter than the 308. In most 308 rifles, the NATO round, loaded to NATO specifications, will show similar, or very slightly lower pressures than the 308 standards.
What guns will shoot the 7.62×39?
If you want to use the Soviet 7.62×39, there are a lot of great options out there for you to consider. The most obvious is an AK47 or a variant of the AK. Ruger has several models of rifles chambered in 7.62×39. The semi-automatic Ruger Mini Thirty and the bolt action Ruger Ranch Rifle come to mind.
A time-tested rifle is the Soviet SKS. It’s a heavy and clunky, but reliable semi-automatic design from the 1940s. There are also ARs chambered for the cartridge. I have been looking at buying an AR upper in 7.62×39 to put on my standard AR lower receiver.
There are tons of options to choose from if you want to take advantage of the cheap ammunition for the soviet round. It’s a fine cartridge and power-wise on par with the American classic 30/30. Just don’t put it in a 308, or a rifle with a 7.62×51 NATO chamber for that matter.
I wrote an article on hunting with the 7,62×39. If you’d like to know more about the cartridge, here’s a link to it.