SPRINCO Buffer Spring - AR-10 Carbine (Orange) Recommended for 9mm AR with 8"-16" barrel Recommended for AR-10 carbine with either 2.5" or 3.25" buffer These springs are an excellent match for AR-10 type guns in .308 or 6.5 with collapsible stocks. Works with both 2.5" and 3.25" buffers as well as our 4.0" 9mm buffers. After extensive testing and evaluation, we found that these springs are properly matched in strength for many 9mm applications. They have the strength, consistent performance and long service life that is needed. Stronger springs hold the 9mm bolt in battery properly and reduce rearward bolt velocity which is important for safety, reduced recoil and service life of triggers. The spring is a critical component of the 9mm blow-back system and you need the highest quality and the proper strength for optimal performance. Sprinco USA Springs are made from certified Chrome Silicon wire stock to ISO 9001:2008 quality standards to withstand extreme heat and high cyclic rate. This ensures consistency in performance through high round counts. They are precision wound, heat treated, stress relieved and shot peened for extremely long service life and then moly plated for improved corrosion and wear resistance. For the longest lasting buffer spring, these are the way to go. Expected service life in excess of 30,000 rounds. Features: Heat Treated Stress Relieved Shot Peened Moly Plated Extremely Long Service Life Compatibility: 9mm Blowback AR15s with Hydraulic Buffer: Recommended for use with 8-16" barrels. AR-10 .308/6.5 Type Carbine with Collapsible Stock: This is also a perfect spring for these firearms. FAQ: What Buffer Spring is best for my build? For PCC builds, we recommend using the strongest buffer spring that cycles reliably and consistently in your build. If it has a bolt catch in use, we recommend ensuring that the spring allows for reliable function of the bolt catch on an empty magazine. If the bolt doesn't lock back on the last round, it is often due to too strong of a buffer spring for your gun and going down a step on spring power usually solves this problem. In PCC builds, there is often some trial and error on buffer spring selection. Every gun cycles somewhat uniquely even with the same build specs. So, there are typical combinations that work well, but you have to see for yourself what works best in your gun with your ammo. For 9mm PCC builds, use an AR10/.308 carbine buffer spring for barrels that are 8" or longer. For shorter barrels, more trial and error is often needed, but some type of .223 carbine spring is normally appropriate. Extra power .223 springs are normally best in all but the softest running systems. For AR15 or AR10 rifle buffer tubes, always use the AR15 rifle buffer and AR15 rifle buffer spring or AR10 rifle buffer and AR10 rifle buffer spring. For AR10 carbines with either the AR15 or AR10/A5 buffer tube, always use an AR10/.308 carbine buffer spring. For AR15 carbines the buffer spring selection is broader and will depend on the specifics of the build. What is the difference between Sprinco Springs and JP Springs: Sprinco Springs use very high quality, certified Chrome Silicon Wire that is cryogenically heat treated, shot peened and moly plated. This gives these springs a very long service life. Running these springs for 10s of thousands of rounds is common. But you do get the typical AR spring twang with these. JP Springs use standard music wire, which is a very good spring material but it doesn't have as long of a service life and is rated at between 5,000 and 10,000 rounds depending on the gun. But the advantage is that they are ground flat on the outer edge which makes them run much smoother and quieter in the buffer tube, so you don't get the annoying spring noise. This is especially noticeable in suppressed guns. So one spring is for max service life and the other is for smoothest running with the least spring noise.