It is a sin to use the word "clip". Thou shall only use the word "clip" only when refering to stripper clips or the M1 Garand.

What does Double Stack mean?
What does Single Stack mean?
What are some of the common single stack magazine types?
What are the some the common double stack magazine types?
How do I load a magazine?
How can I quickly tell if my magazine is fully charged?


What does Double Stack mean?
What does Double Stack mean?

Double Stack is the term used to describe magazines that have rounds positioned in a double configuration as show in the diagram below. This is the configuration used in standard capacity magazines
 
Red Circles represent rounds

What does Single Stack mean?
What does Single Stack mean?

Single Stack is the term used to describe magazines that have rounds positioned in a single configuration as show in the diagram below. This is the configuration used in for low capacity magazines.
 
Red Circles represent rounds

Common Single Stack Magazines Types
A Steel 5 round single stack ribbed magazine
B Steel 10 round single stack ribbed magazine
Clicking on the corosponding link will provide more information

Common Double Stack Magazines Types
Clicking on the corosponding link will provide more information
A Steel 5 round double stack ribbed magazine
B Steel 10 round double stack ribbed magazine
C Steel 20 round double stack ribbed magazine
D Steel 30 round double stack ribbed magazine
E Steel 30 round double stack slabside magazine
F Bakelite 30 round double stack ribbed magazine
G Polymer 30 round double stack waffle magazine
H Steel 40 round double stack ribbed magazine
I Steel 55 round double stack ribbed magazine

How do I load a magazine?
Here is the common way to load a magazine.
This is a picture of an empty magazine, note the follower
Step 1: Place the round in the center of the feed lips
Step 2: Press down firmly until the round snaps into place.
Step 3: The round is now loaded into the magazine.

Step 4: To continue loading repeat the above process.
Make sure that each round is clear of the front of the magazine. If not the magazine will not accept any more rounds.

How can I tell if a magazine is fully loaded?
Other then counting the rounds as they are loaded, if you look at the bottom rear of the magazine you will notice a small hole that is commonly called the "Witness Hole". If you can see a round the magazine is fully charged.
Magazine is not fully charged
Magazine is fully charged, note the round showing through the hole.
 
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