[collegeburner]

For anybody who hasn't heard of them and wants a rough overview of the differences, the 5.7 and 4.6 mostly work on being smaller-caliber at higher velocity. 9mm parabellum usually has muzzle velocity anywhere between 1000 and 1500 ft/s where 4.6 is closer to 2300 ft/s. The 5.7 is closer to 2800. They're also usually steel core.

[ggreer]

I'm pretty sure all the steel core 5.7x28mm is considered armor piercing handgun ammo and is therefore limited to law enforcement.[1] I've never seen steel core versions of it sold at any gun store.

1. https://www.atf.gov/firearms/docs/open-letter/national-jan20...

[collegeburner]

Sadly yeah, it's one in a massive list of stupid laws but FOPA states anything that "may be used in a handgun" if I'm remembering the wording right. I believe they submitted the duty round for the NATO RFP tho and that's steel penetrator. If i remember right blacktip .223 is similarly banned because of AR pistols, you can basically only get AP in full rifle rounds (.30-06) or something like .50 BMG.