By Jim Bullock

I have pressure tested thousands of rounds of ammo in many different calibers both professionally (years ago) and more recently using the facilities of the Canadian Gov't (Explosives Branch) and Expro (maker of IMR powder).

While I don't like sweeping statements, in 308/7.62 I have found that although the specifications have very similar maximum acceptable pressures, the military ammo is usually "hotter".

Commercial ammo tends to run a round 55,000 psi while I have seen some lots of military running around 60,000 psi. (Same pressure gun, observed in the same pressure testing project.)

Ammo specifications can be miss-leading. Military ammo is usually quoted using the CUP system whereas commercial ammo is quoted in psi. The actual pressure maximums are about the same, but the numbers are about 5,000 units apart. This can create the illusion that the military is lower pressure.

The military know what rifles the ammo will be used in and have a guarantee that the rifles will be in good shape. Commercial companies worry about lawsuits. There are rifles in poor condition, miss-matched bolts, unsuitable actions, etc. The last 50 feet per second will cost about 5,000 psi. As a commercial loader I would trade off 50 fps for the safety of 5,000 less pressure, any time. Although commercial ammo can be loaded to 60,000 psi the companies I have discussed this with tell me they don't like to go beyond 57,000 and 55,000 is what they prefer.

The military brass is heavier than commercial brass. I load 308 in commercial brass that weighs 157 grains. I load 7.62 in brass that weighs 195 grains. (I happen to have a large quantity of both types). Since the outside dimensions are the same, we know the internal capacity of the 7.62 case is less because of an extra 38 grains of brass. The powder capacity is very different and the pressure/velocity results of the two are so different I have to treat them as quite different calibers. The light brass can use a larger powder charge and obtain higher velocity at the same peak pressure. The peak pressure of a 308 and a 3006 are the same. The difference is powder capacity. More powder translates to more energy and more velocity. To a lesser extent, the same thing is true of 308 vs. 7.62

Commercial ammo seldom exploits the larger case capacity. In practice I find the military ammo loaded fairly "hot" and commercial ammo is less than max pressure.

Pressure being equal, the military brass offers a significant safety factor. Some actions have chambers with less head support than others, so a thick head is important.

When loading for 303 British the same thing is true about brass weight. Military brass is heavier. Segregate your brass, military vs. commercial and use 2 grains less powder in the military. If you load 3 to 5 grains less than the max powder charge shown in the book you will find the brass lasts much longer. 20 reloads instead of 3 to 5. Just neck size the first quarter inch of the neck, if it is to be shot again in the same rifle.

The suggestion about shooting over a chronograph is an interesting one. If the bullet weight is the same, higher velocity equates to higher pressure, but only if the brass is the same. As I have explained, 308 and 7.62 brass is not the same.

The Hornady Light Magnum ammo I have shot in 308 (both production and experimental) offers significantly higher velocity (around 200 fps) for ordinary pressures (around 55,000 psi). This is accomplished by using a very large charge of compressed slow ball powder. They stuff a 3006 load of slow ball powder into a 308 case. Don't try this at home. You can't do it.

In conclusion, commercial ammo probably has lower pressure than military. Military is safe if the rifle is in good shape. Hornady Light Magnum has unremarkable pressure and I would not hesitate to use it any rifle in good shape.

Handloading and down loading 100 to 200 fps is much easier on the rifle, the brass and the shoulder and is still perfectly fine for punching paper out to 600 yards (about 500 yards farther than is usually required.)

Jim Bullock

About the author:

Jim Bullock is the grandson and son of rifle shooting competitors. Jim started with a BB gun (a daisy pump) in 1950 and received his first .22 at age 10.

He has represented Canada twelve times as a member of the Canadian rifle Team as a shooter, Coach and Team Captain.

His fullbore rifle shooting started in 1960 using the Lee Enfield #4 in 303 caliber in what was known as Service Rifle (B). That was a well-tuned rifle with a Parker Hale 5C rear sight and the standard post front sight. SR (B) was deliberate (no snap, or rapid fire) at 200 to 1,000 yards. His best shot was a pair of bullseyes fired at 1,000 yards with a 26 minute wind change between shots (that is about 260 inches or about 21 feet of windchange).

He has an extensive firearm collection including a dozen or so Lee Enfields.