556 was the measure of the inner diameter of the rifling of a barrel of a gun that shot 556.
Metric is confusing. That’s why for most shotguns, we measure the width by the number of lead spheres of that diameter that would equal one lb, eg a 12 gauge shotgun is the diameter of a 1/12lb sphere of lead.
Nobody knows how big 18.53 mm is, but everyone knows what a 12 gauge shell looks like.
Oh, and gun powder is measured in grains, maybe early smokeless pellets were about the same size as grains of wheat.
Grains as a measure of weight comes from the Troy weight system, think Troy ounce of gold. It is a very old system that for a long time was mostly used by apothecaries and probably has its origins in Ancient Rome.
Grains Apothecary is used to measure powder charge weight is because it was a “fine” enough scale for measuring small amounts of things that if you get it even a tiny bit wrong, can kill you. So, ammunition manufacturer’s looked around and scales used for accurately measuring small amounts of drugs were commonly available, so they went with that.
Cool side point: Powder charges are checked by weight and dosed out, (or thrown), by volume as it has always been done since the first gonnes were a thing.
The case is both shorter and narrower than 556/223, so it won’t even sit right in anything not designed for it. But FN makes quite a few guns that use it.
then why is it called 556 if its actually 5.7?
556 was the measure of the inner diameter of the rifling of a barrel of a gun that shot 556.
Metric is confusing. That’s why for most shotguns, we measure the width by the number of lead spheres of that diameter that would equal one lb, eg a 12 gauge shotgun is the diameter of a 1/12lb sphere of lead.
Nobody knows how big 18.53 mm is, but everyone knows what a 12 gauge shell looks like.
Oh, and gun powder is measured in grains, maybe early smokeless pellets were about the same size as grains of wheat.
The problem is it’s impossible to tell whether you’re joking or being serious
Mostly.
He’s correct and showing the…quirks of the system.
say it ain’t so!
Grains as a measure of weight comes from the Troy weight system, think Troy ounce of gold. It is a very old system that for a long time was mostly used by apothecaries and probably has its origins in Ancient Rome.
Grains Apothecary is used to measure powder charge weight is because it was a “fine” enough scale for measuring small amounts of things that if you get it even a tiny bit wrong, can kill you. So, ammunition manufacturer’s looked around and scales used for accurately measuring small amounts of drugs were commonly available, so they went with that.
Cool side point: Powder charges are checked by weight and dosed out, (or thrown), by volume as it has always been done since the first gonnes were a thing.
Maybe the original was 5.56mm and some dumbass decide “nah, not enough b u l l e t, better make it 5.7mm.”
OK, so there is a 5.7mm, that’s the same diameter as 5.56/.223, but it’s not compatible with either because of the french.
I look into it. 5.7 is shorter than a .223 and is a much smaller grain.
Kinda?
The case is both shorter and narrower than 556/223, so it won’t even sit right in anything not designed for it. But FN makes quite a few guns that use it.