Was browsing around looking for a case lot of 5.56 and noticed a few vendors describing some rounds as magnetic or non.  Never noticed this before.  What is the significance?

Heads use ferrous metals for core.  They attract magnets. Increase risk for sparks on the range and possibly starting a fire.  Also, density makes them tough on the backstop at the range.

Steel penetrator SS109-tipped rounds (M855 type) are tough on AR500 plates.

Ask me how I know ...

A lot of people describe ammo as being magnetic or non magnetic, but as Bill said, what they are trying to say is the the ammo either attracts a magnet or it doesn't.

Damn.  I was hoping I could improve my aim against robots.  A near miss would be attracted to the bot and swerve to hit it.

 

Oh well.

Heads use ferrous metals for core. They attract magnets. Increase risk for sparks on the range and possibly starting a fire. Also, density makes them tough on the backstop at the range.

Is it really the density or that steel has significantly higher tensile strength and thus are more like to penetrate?

Is it really the density or that steel has significantly higher tensile strength and thus are more like to penetrate?

 

The steel is actually less dense. Very few things are more dense than lead, and the only one I know of off the top of my head is tungsten.

 

Anyway, I would suspect that it is the hardness of the steel penetrator that beats up backstops. Lead is obviously very soft, and I've read that M855 uses a very hard steel alloy. Steel commie stuff uses a very mild alloy.

 

Also, most Eastern Bloc ammo uses bimetal jackets that attract a magnet. 

Depleted Uranium is 68% denser than lead.

Depleted Uranium is 68% denser than lead.

So's my ex.girlfriend

 

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Anyway, I would suspect that it is the hardness of the steel penetrator that beats up backstops. Lead is obviously very soft, and I've read that M855 uses a very hard steel alloy. Steel commie stuff uses a very mild alloy.

You have indeed heard that and possibly also even read it stated authoritatively in published descriptions of M855. But it is BS. The steel insert in M855 is mild steel (with a flat tip) and always has been. M193 (all lead bullet except jacket/misc.) penetrates common objects more than M855 out to at least 200 yards, including penetrating more steel. I actual did little fun test a couple months ago and the difference in penetration of steel was like night and day. It's not a small one.