Written by New Product Development Manager Mark Walker
Recently I have noticed a few threads on shooting forums that discuss the advantages of replacing the firing pin springs in your rifles on a regular basis. This is to make sure that the springs are in good operating order and provide proper energy to the primer when the cartridge is fired. Some of the stated advantages included lower velocity extreme spreads, lower standard deviations, and improved accuracy over worn out springs.
In our range here at Sierra Bullets, we replace springs on a regular basis as preventative maintenance. However, I was curious to see if there would be a visible improvement when replacing a spring that had been in service for a while. I looked over our gunsmithing log and found an action that had close to 40,000 rounds on it without changing the spring. This action always seemed to shoot no matter what type of barrel we installed on it and the current barrel was no different. I figured that if any improvement could be gained by changing the spring, this rifle would show it on target.
Since the action is a trued Remington short action Model 700, we always have spare springs on hand so I grabbed one and headed to our range. We installed the action into one of our return to battery rests and set about deciding how to perform the test.
Since time was somewhat limited, it was decided to load up sixty rounds of ammunition and shoot six five-round groups using the old spring and six five-round groups at 100 yards using the new spring. We used the old standby #2200 30 cal 168 gr HPBT as the bullet of choice loaded over a charge of 40 grains of 4064 powder. All ammunition was loaded at one time and all bullets were out of the same lot to make things as consistent as possible.
After looking at the cleaning log, we decided not to clean the barrel during the test since the rifle had fifty rounds on it since it had been cleaned. The first target showing the results of the old spring is shown here.
Average group size was 0.393, 28 extreme spread, and 11 standard deviation over the six groups. The rifle is capable of shooting a little better than this with some tuning however all we were concerned with is if the new spring could improve on the data we collected from the old spring.
After shooting the first target, the bolt was removed and the firing pin spring replaced.
This picture shows the old spring alongside the new spring. The old spring had compressed about three full coils when compared to the new one. Once we completed the spring swap, we went back to shooting.
The next target showing the results of the new spring.
Average group size was 0.378, 29 extreme spread, and 11.6 standard deviation over the six groups. Once again the rifle is capable of shooting better but we were looking for any sign of improvement when using the new spring.
Comparing the data we see that the group size did improve slightly when using the new spring however the extreme spread and standard deviation were actually slightly worse. Now I realize that this test is far from complete and it would take hundreds of rounds fired over several days with many different loads to get a statistically meaningful result. However we can see that the new spring did not make a drastic difference in the loads here. All this being said, I still swap the springs in my competitive rifles on a regular basis to make sure there are no problems during a match.