FWIW... 100% my favorite recoil spring. I use them in all my AR's, 9MM, 308 / 6.5CM, 300BK, and .223 / 5.56.
Your Flatwire recoil springs have always produced 100% positive function.
Thank You Mr. Tubbs for making them.
Any history you could share about them ? I would be genuinely...