When it comes to magazine maintenance, there are two primary schools of thought. One is that magazines are a fungible commodity, and should be replaced when they start showing signs of wear. The second school of thought hates to let go of a good piece of kit, especially when replacement springs are nearly an order of magnitude cheaper than a new magazine.
David Tubb's AR-15 Flatwire Magazine Spring offers full 30-round capacity function with positive pre-load against the follower. While these are pricier than bulk replacement springs, the 17-7 stainless construction is designed to offer superior wear, and passes the U.S. Military's 96-hour saltwater bath test.
The company claims that not only will the flatwire spring allow full loading of 30 rounds in magazines so designed, but in most magazines the spring will allow loading beyond 30 rounds. The flat nature of the spring allows it to lay flatter in the magazine body, offering up to 32 rounds in a standard magazine.