I use the Geissele Super 42 buffer spring in all my AR15s. I suggest other AR15 users try it. It gets rid of the twang sound and makes the spring last longer than regular springs.
Geissele Super 42 Spring Specs
- Length: 3.427" (normal size)
- Body width: 0.687" (normal size)
- "Collar" width: 0.762" (a bit smaller than normal)
- Weight: 3.78oz

The "collar" is smaller, so the thick spring fits better. If you use a different buffer, it might get stuck. You can't buy just the buffer. If yours breaks, you have to buy the whole set again. Or change the weight inside yourself.
Only 3 buffer weight options are available, the H2 is the best for most non suppressed AR15 builds. Depend on the gas system, you may have to go for the H1 or H3. However, it also depends on your ammo type, barrel length, gas amount and bolt weight to optimize the performance. So it's never one size fits all if you get serious with suppressed shooting.
Geissele Super 42 Spring Weight

Normal springs push with about 11-13 lbs. when the bolt is all the way back and 6 lbs. when the bolt is closed. The Super 42 spring pushes with 15 lbs. when the bolt is all the way back and 7.5 lbs. when it's closed. That's 25% stronger than a regular spring. There are other springs like Sprinco's that cost about $20 and are just as strong.

Twang Sound Elimination
The twang sound or vibration is definitely reduced. My AR15 uses the Magpul UBR stock with additional polymer around the aluminum buffer tube.
The Geissele Super 42 spring is definitely better than a flatwire spring, and many users agree with that. If you are a casual shooter may ask: "Does it really matter"?
If you're a casual shooter, this may not be an issue if you aren't consciously look for the problem. Most casual shooters who don't know about it until someone points it out. Otherwise, they wouldn't notice.
Super 42 Braided Wire Design Philosophy
The braided sprig wire design is inspired by the German MG42 machine gun. These wires move on their own, soaking up extra energy. This means the spring is less likely to break, making your rifle work better in high volume firing.
It also optimize the harmonics of the spring so the node oscillation doesn't collide into each other, which is the main reasons for the spring twang sound in the buffer tube.
When you compare it to the usual spring, the Super 42 Spring doesn't get shorter or weaker quickly. Based on the claim, the Super 42
Final Verdict

Some experts say braided springs last longer than round ones especially for high rate of fire shooting. Flat springs also last longer than round ones. But do we need them to last longer than the typical round volume you shoot?
If you shoot less to wear out your spring, it's not necessary to go out of your way to upgrade. If you shoot a lot, and you shoot suppressed, and you don't like the recoil spring twang sound. The Geissele Super 42 is a good option.