If these are new mags, and they're packed in a slightly sticky, pasty, yellowish, and foul-smelling preservative, it's most likely cosmoline, the same stuff used to preserve vintage military rifles.
Cosmo can be removed using a variety of common solvents such as brake cleaner, mineral spirits, or acetone, but IMHO the easiest and cleanest way to remove it is to dip the parts in boiling water. Disassemble the mags and set any plastic parts aside. You'll want to do this outside and either boil the metal parts in a pot that you never use for cooking, OR put the parts in a metal or glass container and then fill it with boiling water. The cosmo will melt off and float to the top of the water; stir the parts gently to make sure you get it all. Thoroughly dry and oil the metal parts afterwards and reassemble.
All that being said...
I'm generally with Sparks1957. I usually don't do the full-blown cosmo removal treatment on new mags; I just disassemble them, wipe everything down really well, lightly oil, reassemble, and call it good.