About the only gun I remember that used strippers was the 1903 Springfield with its internal box magazine, but it was .30-06 Springfield...
However, I do remember that back then they liked to ship ammo in 5-round clips. Federal Lake City loads 10-round clips with 5.56x45 ammo even to this day... So that's probably all it is. Just an easier way of carrying ammo without having to carry loose rattling rounds around with you.
Lake City Ammo 5.56x45mm NATO 62 Grain XM855 SS109 Penetrator Full
If you are that new to reloading, I suggest watching LOTS of YouTube videos and reading as much info as you can, before you even prime a case...
Reloading can be dangerous for you and for others. ALWAYS go by the manual when reloading. I recommend the Nosler 7 reloading manual. But I always shoot Nosler bullets out of just about everything. Speer makes a good one, so does Hornady, Berger, etc... Always double and triple check everything. Nobody wants to see anyone get hurt, so I'm just giving you a few pointers. Check out IraqVeteran8888's YouTube page, he has TONS of reloading basics videos and also a few tips that are very helpful.
Also, if you are reloading for your bolt-actions, I suggest RCBS Neck-Sizer die sets, your reloads will be more accurate, plus it makes your brass last longer. If loading for an AR, use the RCBS AR-Series Small-Base die sets. And for pistols...ALWAYS buy carbide dies.
These are just a few tips I've learned from other loaders when I was first getting started.