The Secret to a Long Life?: A Garand Diet or What to Feed Your M1 Garand (Part I)

So you’re thinking of honoring America’s military and manufacturing heritage, shugging government regulators, putting a little money into a good investment and opening the door to a world of new shooting games, which is just another way of saying, you’re thinking about getting (or have already got) an M1 Garand.  Good for you, kid.  Now given it’s 2011, what are you going shoot out of it?

I rarely speak in absolutes, but for this special four part look at a healthy diet for your current or soon to be purchased M1 Garand, I’ve got one for you here:

Do not shoot standard commercial .30-06 in your Garand. The semiautomatic cycling of the Garand is driven by the gases produced by the burning propellant of the cartridge. The rifle’s gas system is ported and balanced for a specific range of gas pressure, volume and burn rate, and commercial .30-06, intended for hunting and bolt action rifles, can exceed that range, causing damage to the operating rod, and of course worse.

Perhaps not coincidentally, according to gunsmiths and former armorers I’ve spoken with or read, the number one cause of cycling problems in Garands is a bent op rod. The op rod is connected to the bolt which, of course, rides in the receiver; shoot enough overpressure ammo in your Garand and you can damage these, too.

So what’s the solution?

Your choices are to stockpile ever-dwindling supplies of surplus M2 Ball ammunition; snatch up all the Frankford Arsenal and Lake City M72 military match ammo that comes within your reach; shoot commercial ammo specifically designed and loaded for the Garand; or handload. I do all four. There’s another interesting option available, but I’ll save that for the end so stay tuned.

Gas

The foundation for the “no commercial ammo in the Garand” advice lies with the difference between the Garand’s design coupled with Army specifications for ammunition pressures, and the Sporting Arms and Ammunition Manufacturer’s Institute, Inc. (SAAMI) specifications for modern .30-06 ammunition.

The Army’s maximum allowable pressure for its .30-06 ammunition (M2 Ball) is 50,000psi, with a maximum proof test load pressure set at 67,500psi. In testing, Townsend Whelen found that M2 breech pressures were actually “about 42,000 pounds.” The SAAMI standard for .30-06, however, is 60,000psi maximum average pressure (see sidebar), and the SAAMI standard for rifle cartridge proof loads is 33 to 44 percent above the maximum average pressure (MAP) for any particular cartridge (in the .30-06, that proof load pressure is as high as 86,400psi)3. As you can see, at 60,000psi the SAAMI allowable pressure is almost half again as much as M2s maximum pressure, is 20 percent higher than the maximum allowed in the Garand, and approaches government proof load pressure. So, it’s not too much of a stretch to think of shooting commercial .30-06 hunting ammunition in the Garand as pretty much feeding the rifle a diet of proof loads.

Also, when we talk about safe gas pressures in the Garand, we’re concerned with, not just peak pressure, but the pressure curve. That is, we’re concerned about the combination of force (gas pressure) and the rate at which it is applied to the gas system. John C. Garand designed his rifle to operate properly with a pressure curve that won’t bash the gas system components around too hard.

As the M2s original 42,000psi pushes the bullet down the bore, the increasing volume between the chamber and the bullet drops the pressure to about 8,000psi near the muzzle, where a port taps off about 6,000psi (+/- 2,000psi)4  worth of that to operate the Garand’s gas system. The gas pushes on the op rod, essentially a long piston connected to the bolt, driving the bolt backward to extract and eject the empty case and compressing the recoil spring inside the op rod. The spring then pushes the op rod forward again, pulling the bolt with it to strip off and chamber a fresh cartridge.

All of this is in balance – the gas pressure, the port size, the op rod diameter and length, the recoil spring strength. Vary any one of these too much, and the system fails to operate properly.

Powder

Now that we’ve established what we don’t want, let’s talk about what’s appropriate for shooting in the Garand.

Military M2 Ball ammunition launches a 150gr FMJ bullet at 2,740fps, using 50gr of IMR 4895.1 Military M72 Match ammunition featured a 173gr bullet launched at 2640fps; the powder was, again, IMR 4895 and again listed as a 50gr charge. This next bit is extremely important, and the reason why there is sometimes confusion over powder charge weights in military .30 caliber ammo. Though the Army ostensibly set IMR 4895 charge weights at a nominal 50gr, the powder charge weights in the M2 and M72 loadings actually varied over the years because of variances in the burning properties of different lots of powder. Interestingly, in the nine years of M72 production using IMR 4895 (1957-1966), the charge weights apparently never even reached 50gr, instead varying from 46gr to 48.5gr.

Another place where confusion arises and elicits naughty words from anonymous gun forum posters is with other military ammunition used in the Garand. Tracer ammunition utilized IMR 4895 or WC 852; armor piercing and armor piercing incendiary ammo had WC 852 powder; the frangible round was loaded with SR 4795; the dummy round for launching grenades used 45gr of IMR 4895; and the standard proof test round was loaded with 52gr of IMR 4198 for that wincing 67,500psi of overpressure.1 I’ve seen forum posters cite or ask about these loadings, but none of them are appropriate for duplicating M2 or M72 loads  (though it’s interesting to note the grenade launching dummy round is in the ballpark).

Powders, of course, burn at different rates (speeds), producing not just different peak pressures, but also differing in the amount of time it takes to reach a maximum pressure level. This is why we have “fast” powders for pistol cartridges and “slow” powders for magnum cartridges. If peak pressures were our only concerns, there would only need to be a handful of different powders out there. Instead, we have more than a hundred to choose from, and they are classified by burning rate, fastest to slowest.

I’ve illustrated burn rate to others by laying out a line of extruded rifle powder a couple feet long that terminates in a small pile of black powder. I light the end of the line with a match and we watch the rifle powder take several seconds to burn its way to the pile; when the flame reaches the black powder, the entire pile goes up in an instantaneous flash because black powder burns so much faster than modern powders.

In the Garand, a too-fast powder will produce too much pressure before it can send the bullet downrange at a decent velocity; too slow a powder will get you the velocity, but at too high a pressure. Powders with a burn rate appropriate for the Garand are those between IMR 3031 (fastest) and IMR 4320 (slowest).

According to the Hodgdon chart of propellant burn rates there are 22 different powders available to us that fall within this parameter. IMR 4895, used in the M2 Ball and M72 Match loads, falls smack in the middle of the group and it’s a logical place to start. And finish, for that matter, unless you want to fine tune a match load or are entertained by reinventing the wheel. Keep in mind that trying to work up an awesome gnats-ass match load for an ordinary surplus Garand becomes a pearls-before-swine thing at some point.

Art Merrill has been shooting Garands since he bought his $162 DCM Garand in 1987; he competes regularly with the Garand and is a CMP Garand-Springfield-Military Master Instructor. He’s been a handloader and Highpower and Long Range competitor for 25 years. A list of source material will follow the final installment of this series.