What is the best way to clean older USGI 30 round magazines?

After dissassembly: mineral spirits soak, parts washer, hot soapy tap water????

I have a few used magazines that have sand in them and they require a thorough cleaning.

Disassemble.  Drop the mag bodies and followers in a sink of hot soapy water.

Scrub the insides with a bottle brush.  Check the followers, if needed, use a hand brush (fingernail brush) to scrub clean.  Set aside to dry.

Wipe the springs with a slighly oily cloth.  Old English Furniture Oil is a good oil for this.  I keep an old T-shirt rag dampened with Old English for wiping down firearms after handling.  It prevents fingerprints from rusting spots on blued steel, and is good for wood furniture, too.

Do not lubricate the mag in any way.  The little bit of oil on the springs is just for rust prevention.

If you just must lubricate your mags, spray the inside with any of the dry teflon sprays available.

If you are in a rush, or are going to reassemble asap, put the mags in your oven set as low as possible, 150*F - 170*F for an hour will help dry them.