Magazines have parts that will wear out and reduce reliability. A few simple steps and some cheap parts can return a beat up magazine to reliable service. Total cost of replacement parts was $3.00. A parachute cord magazine pull was added as an enhancement, and total cost for those parts was under $1.00.
Step 1: Gather Required Parts and Tools
Minimum requirement is a replacement magazine spring. Parts and tools shown are: paper towels, knife, rescue hook, industrial Sharpie, lighter, 100MPH tape, ziptie, parachute cord (paracord), toothbrush, screwdriver, paracord template, magazine, Magpul Enhanced Self Leveling Follower, and new magazine spring.
Step 2: Dissasemble Magazine
Use a screwdriver to pry the magazine baseplate off. Be sure to use you hand to catch the spring.
Step 3: Check Spring and Magazine Body
Springs will take a set and become less effective over time. Compare the old spring to a known good or new spring. In this case, the old spring has taken about 1.25" of set. It's toast.
Check the magazine body before proceeding. Be sure feed lips are straight and do not show any signs of cracking. Check the body for any dents or bends. If the feed lips have a minor dent, you can true them, but otherwise trash the whole mag if there are any signs of major damage.
Step 4: Clean the Inside of the Magazine Body
Clean the insides with a brush and rough patch or paper towel. Don't use oil or solvents, just dry bush to knock out carbon and debris.
Step 5: Prepare the Paracord for Use As a Magazine Pull
Using the template (length depends on preference and size of ziptie), cut a section of paracord off with a sharp tool. Strip the paracord of it's internal strands. Use a lighter to seal the ends to prevent fraying. Cut the locking end of the ziptie off and slip the ziptie into the paracord. Tie each end off with a tight, small knot.
Step 6: Reassemble the Magazine
Get parts ready and begin reassembly. Drop the follower into the magazine body and compress the spring. Slide the baseplate on about halfway. Insert the knot ends of the paracord between the baseplate and magazine body. Slide the baseplate back on all the way and test the paracord; it should be firmly attached to the magazine.
Step 7: Test Function
Use a sturdy stick (toothbrush, cleaning rod section, etc) to ride the follower up and down the magazine body about a dozen times. The action should be smooth, with no kinks, and the spring should provide a good amount of resistance.
Take some tape (100MPH, duct tape, gaffers tape) and wrap the base of the magazine. This will help provide some friction for magazine handling, as well as reduce rattle and improve noise discipline. It's also a handy place to mark you magazine.
Use a marker to put an identifying mark on the magazine. Number them as well to keep track of magazines and weed out a troubled mag.
Live fire testing should be conducted with the magazine before it's returned to active service.