Depending upon what they are trying to achieve with the spring design and the envelope they are working with, those designing compression springs for the firearms industry sometimes try to “fit 10 pounds into an 8 pound box” – by designing a spring that simply cannot handle the load and stress and give a reasonable life. Many spring designs are overstressed, approaching the limit of the spring design capability when designers want to do more than is theoretically possible with the space assigned for the spring. In an area that is three inches high and a half-inch wide, they may be designing a spring that requires five inches of space. With an overstressed design, the spring will take a permanent set, losing its length and load.
To guard against this, spring manufacturers frequently undertake significant development and prototyping to assist the customer accomplish the right spring design.
For example, one major firearms manufacturer began its design process for a 40 millimeter (mm) pistol recoil spring using standard music wire. Standard music wire often just does not have high enough tensile strength to support load requirements and testing indicated the spring could not take the shock. During the spring consultation and prototyping phases of the design process, Connecticut Spring & Stamping CSS, which has a 70-year history and diverse expertise in developing stranded wire and shaped wire springs, recommended the use of chrome silicon flat wire. The chrome silicon material, widely used in the manufacturing of pistons in the automobile industry, can withstand higher heat and shock than music wire. The firearms manufacturer adopted the recommendation and the spring made from the chrome silicon flat wire was successful.
Figure 2: Spring developed from chrome silicon flat wire for a 40-mm pistol recoil
Another example was developed for a prominent 45 caliber pistol OEM, which started out using stranded music wire for its recoil spring. Testing showed that the material would not stand up and keep the load. While it wasn’t fracturing, the wire’s tensile strength was just a bit too low. A material change to rocket wire enabled the spring to achieve a higher load.
Figure 3: Spring developed from rocket wire for a 45 caliber pistol OEM