That sounded cool to me, and what I really wanted anyway was the manual, a few details for a story, what my editor called pixie dust. And if I could irritate the gun-banners, so much the better.
Well, that's all well and good, but then I decided to shoot the thing. And I had no idea what ammo to use or even how to load the magazines.
Ironically, I turned to Google since I had trouble reading the rifle's manual -- small print and all. I learned that the military version of this rifle shoots 5.56 x 45mm ammo, while the civilian version shoots .223 Remington. Many claim these rounds are the same. .223 Remington = 5.56mm. Metric vs. Standard.
So I bought a bit of commercial and a bit of military -- usually much cheaper than commercial ammo -- and I blasted away, scaring the hell out of myself with the first round because I hadn't thought to wear muffs. Big mistake: These things are loud.
Then a few articles in gun fora caught my eye. Turns out, there is a difference between military 5.56 rounds and civilian .223 rounds, a big one, one which might ruin your gun if you shoot the wrong ammo... or be dangerous.
While these rounds have nearly identical overall dimensions, the NATO-spec 5.56mm chamber is slightly larger than the SAAMI-spec chamber for the .223 Remington. Shooting 5.56 ammo in guns chambered for the .223 will generally exceed pressure levels established by SAAMI. Too much cartridge pressure and the case expands, perhaps jamming chamber and bolt, deforming both and maybe the barrel. Or, the rifle could blow up. At a minimum, you're accelerating the wear-rate of your rifle. With firearms, that's not a good thing.
So which one to shoot in my Bushmaster? The articles said to look at the barrel, the correct type of ammo is specified. Mine said "5.56/.223."
What the hell did that mean?
So I called Bushmaster. Simple answer: Some rifles are designed to shoot both. But I was warned that if my rifle said ".223" only, not to shoot 5.56 military ammo through it, especially if the ammo is lead-free -- those rounds are loaded to even higher pressures than normal commercial ammo.
How many people know this? Evidently, not many, because at the range I ask the question, often of people decked out in mall ninja duds blasting off rounds from their AR-15s as fast as they can pull their triggers -- sometimes their barrels glow orange or red.
The response is usually a blank look. If they look at their barrel at all, they may add, "Son of a gun..."
So, the rule is: Do not shoot .556 military ammo in a chamber designed for .223 only.
A few years later, I got into guns in a big way and bought both a Springfield M1A and an ArmaLite AR-10, both 7.62 X 51mm NATO rifles ("7.62 NATO"), the commercial version being the very popular .308. Both are great battle rifles, and the round is much more favored among our troops because it's more powerful than the 5.56, which often may not penetrate windshields or body armor. 7.62 NATO has no such issues, and it's more powerful, accurate and faster than the AK-47 round (7.62 X 39mm) our enemies tend to shoot.
So I had the same question: Are the military and commercial rounds the same, other than Geneva Treaty differences (mandating full metal jacket rounds for military use, i.e. no hollow-points)?
Again, they are not. Shooting .308 Remington commercial rounds in a rifle chambered for 7.62 NATO may cause a potentially catastrophic over-pressure situation. In both cases, my rifles said "7.62 NATO," and I'd bought a load of .308 ammo. In contrast, I only had one rifle -- a bolt-action hunting rifle -- chambered in .308.
Was I in danger using my .308 ammo in my two 7.62 NATO rifles? I called both Springfield and ArmaLite. Both advised that while my concerns were real, both rifles were chamber head-spaced for the .308, so were safe with either ammo.
ArmaLite and Springfield were thinking ahead. Problem is, not all .308/7.62 NATO rifle manufacturers have considered this difference, and not all rifles chambered for 7.62 NATO are safe with .308 commercial ammo.
Rule: Do not shoot commercial .308 ammo in a rifle chambered for 7.62 NATO without calling the manufacturer and asking. Again, this is especially true for lead-free steel ammo.
There's a solution of course: a different op-rod or military surplus or Garand-designed ammo.
I did all three.
Rule: Don't shoot modern commercial ammo in an M-1 Garand, unless you've installed the correct operating rod or you've bought special Garand ammo. Use military surplus instead.