A reader of our magazine recently asked us about loading for the M1A. He pointed out that many articles caution against using some powders in the M1 Garand because doing so can bend the operating rod. If that's the case, he asked, why is there no such caveat for the M1A?
For starters, yes, slow-burning powders can be dangerous in the M1 Garand. This rifle was designed to function within a specific cyclic parameter. These cyclic rates are achieved by using medium burn-rate propellants such as the various 4895s.
With appropriate powder, the pressure peak occurs early and drops off well before the bullet passes the gas port. However, if you load the Garand with a slow-burning powder, the pressure peak occurs later and lasts longer — resulting in significantly higher pressures flowing through the gas port and into the operating system. Operating rods bend, parts crack and break.
The M1A — a Springfield Armory-trademarked designation for the civilian version of the M14 — is the most widespread M14 action used by recreational and competition shooters in the United States. It differs from the M1 Garand in several aspects, not the least of which is the fact that the Garand is chambered in .30-06 and the M1A in .308. However, the two aren't entirely dissimilar, and the question of whether the M1A is susceptible to damage from the use of slow-burning powders is legitimate.
To help answer the question, I turned to Hodgdon's propellant guru Ron Reiber and Hornady's lead cartridge design engineer, and vintage rifle savant, Dave Emary. I also relied heavily on Glen Zediker's publication Reloading for the Match M14. Zediker is known as an early ambassador for using accurized M16s in service rifle competition, but he is vastly experienced with and still a proponent of the M14/M1A.
In short, the answer to the reader's question is that while propellant choice and charge caveats do apply to the M1A, the M1A is much less susceptible to damage than the M1 Garand.
Why? Emary explained it this way: "The M1A op rod is only about 40 percent as long as the Garand, which is the biggest reason. It's more of a short-stroke piston design and only has to travel about three-quarters inch before it begins venting gas. The Garand's op rod has to travel at least twice that far before it begins to vent. The M1A has a much more forgiving system, with less of a weak link."
But even so, there are considerations for reloading for the M1A, beginning with case selection. There are two ways to look at case selection when reloading for M1A rifles. Zediker suggests sticking with military-type brass, such as Lake City or IMI, which has a heavy web and is constructed of a hard alloy. Such cases resist pressure and deformation well (M1As are notoriously hard on brass).
Emary — who earned the President's 100 badge with an M1A in 1997, when accurized M16s/AR-15s were already dominating service-rifle competition — prefers to use commercial Hornady or Winchester brass. He says the greater case capacity allows him to achieve better performance levels at lower pressures.
Whichever way you go, be sure to full-length size every case, preferably with a small-base die. Contrary to conventional wisdom, sizing with a small-base die may actually improve accuracy, particularly if your rifle is one of the many M1As with a slightly oval chamber.
A custom small-base die with interchangeable neck bushings is ideal. Setting the shoulder back adequately while sizing, and priming with hard Winchesters or CCI primers helps avoid slam firing — another topic entirely.
Trimming after every firing is also a good idea. M1A bolts begin unlocking while the chamber is still pressurized, which often leads to considerable case stretch. Finally, don't reload cases fired from an M14 more than four or five times, even if they pass visual inspection.
Next we deal with the crux of our reader's question: propellant selection. Paraphrasing Zediker, low chamber pressures do not necessarily mean low port pressures and vice versa. Some slow-burning powders, which generally have low chamber pressures, can escalate port pressures well above the limit for the M1A — just like in the M1 Garand.
This has to do with the amount of gas pressure behind the bullet, which is higher with a "late blooming" powder. When M1A port pressure is too high, the piston, operating rod and bolt all move too fast and too hard — resulting in excessive wear on the gun. It's harder on cases, too, because the bolt unlocks and begins extraction early.
What is too slow? According to Zediker, IMR 4064 is the slowest suitable powder; Varget is too slow. Emary disagrees, saying IMR 4064 and Varget have basically identical burn rates. Reloder 15 is on the edge, as are powders such as Reloder 16, N140 and N150. Powders such as 4320 and Reloder 17 cross the tipping point and should not be used.
"Powders effective in the .308 have a much narrower burn rate range than those useful in the .30-06 cartridge," Emary says. "Unlike the .30-06 — which has the case capacity to effectively use a vast spectrum of propellants — you can't put a very slow burn-rate powder in the .308 and get much advantage. As a result, it's harder to screw up when loading .308 cartridges for an M1A than when loading .30-06 rounds for an M1 Garand.
"However," Emary continues, "if you shoot heavy charges of slower burn-rate powders with heavier bullets in your M1A, over time you'll eventually see some peening and so forth. Plus, your bedding can begin to break down. However, most guys aren't going to do that because such loads are just no fun to shoot."
Time-proven best performers in the M1A are the various 4895 powders. Zediker's favorite is H4895, which meters well and has the temp-resistant treatment of Hodgdon's Extreme line.
"Tune the charge to produce about 2,550 fps with a 168-grain Sierra HPBT bullet and accuracy will follow," he writes in his book. This is in low-capacity Lake City or IMI brass.
Reiber pointed out that while the .308 is SAAMI spec'd at 62,000 psi maximum chamber pressure, best M1A charge weights are found at about 48,000 to 50,000 psi — typically around two-thirds up through the load data range.
Want an easier resource? Hornady's reloading manuals (No. 7 through current) contain a special "service rifle" section dedicated to loading the .308 for M1A rifles.
Powder isn't the only port-pressure-elevating culprit. Without modification by a savvy gunsmith versed in tuning specialty M1As, heavy bullets such as 190-grainers can overwork the operating system. As Zediker put it: "I'd keep the 190s away from any M14 I had to pay for."
And that's not an issue because today's 168- through 178-grain low-drag bullets are so good that heavy projectiles like the 190s no longer offer the long-distance ballistic advantage they used to.