this post was submitted on 01 Apr 2024
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[–] [email protected] 18 points 8 months ago (2 children)

then why is it called 556 if its actually 5.7?

[–] [email protected] 31 points 8 months ago* (last edited 8 months ago) (2 children)

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.

[–] [email protected] 30 points 8 months ago (3 children)

The problem is it's impossible to tell whether you're joking or being serious

[–] [email protected] 13 points 8 months ago
[–] [email protected] 2 points 8 months ago (1 children)

He's correct and showing the...quirks of the system.

[–] [email protected] 2 points 8 months ago

say it ain't so!

[–] [email protected] 8 points 8 months ago (1 children)

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.

[–] [email protected] 1 points 8 months ago

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.

[–] [email protected] 6 points 8 months ago (1 children)

Maybe the original was 5.56mm and some dumbass decide "nah, not enough b u l l e t, better make it 5.7mm."

[–] [email protected] 6 points 8 months ago (1 children)

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.

[–] [email protected] 2 points 8 months ago* (last edited 8 months ago) (1 children)

I look into it. 5.7 is shorter than a .223 and is a much smaller grain.

[–] [email protected] 2 points 8 months ago

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.