I feel like 7.62x51mm NATO vs .308 Winchester ammo is possible the greatest debate of all time. Seriously, if you asked 3 different gun owners you’d probably hear “it’s the same thing”, “they are completely different”, or “it doesn’t matter”. Well, I’m going to spark a flame here and tell you, they are indeed different.
But to really understand the difference, you have to know the history. During the 1940s, with World War II raging, engineers were trying to figure out how to prove the fire power of rifles such as the M1 Garand. The US troops were utilizing .30-06 Springfield rounds for there gun and they were performing well enough that they did not want them replaced. However, the most common complaint was the limited capacity, which only allowed for 8 rounds in a clip.
Several different rounds were created, but the first being the .300 Savage, with the T65 series experimental cartridges. This round would lead to the development of the 7.62x51mm NATO round. At the same time, the engineers at Winchester were working on their own round, the .308, as they saw a market for a civilian model. Winchester branded it’s cartridge as the .308 Winchester and marketed it to the commercial hunting industry.
The differences are marginal. In terms of pressure, you’ll often find the 7.62x51mm NATO ammo shown as 50,000 PSI while it’s 62,000 PSI for the .308 Winchester. In terms of case thickness, a 7.62x51mm NATO round will be thicker than the .308 Winchester. But possibly the biggest difference will be the headspace, which is probably the most important difference. The .308 Winchester headspace is 1.630 inches while for a 7.62x51mm NATO it is 1.6355 inches. Headspace is important because if it’s too long for a cartridge it will float the round back and forth in the chamber, but if it’s too small the bolt won’t close properly and will need excess force to close it. This gets dangerous because with thinner brass, it can cause the round to rupture and then you have a big mess.
Here’s where things get confusing, the dimensions of the .308 Winchester are almost the same as the 7.62x51mm NATO round. The chamber of the .308 Winchester has a slightly shorter headspace and thinner case walls. This will allow 7.62x51mm NATO ammo to feed reliably in rifles that are chambered for .308 Winchester but .308 Winchester ammo will rupture when fired in rifles chambered for 7.62x51mm NATO.
Bottom line, they are two different cartridges. If you want to be safe, use only the ammo that your gun is chambered for. Happy shooting!
Ben