M
MKnarr
Guest
I had a private discussion with what I believe to be a valued member of the forum about ignition on my Anschutz. To be up front, I am not a true benchrest shooter but compete very seriously at 22 Benchrest Silhouette at 65, 75, 100, 150 and 200 meters. I have been on the top of my game for the last 3 years but as many of you know, you can never stop trying to improve your equipment or skills.
To that end, the discussion revolved around the firing pin spring and the lack of lubricant on the inside of the bolt. I realize this might be old hat to many of you but the experiment I performed may surprise you anyway.
The rifle I use is a 1970 Anschutz model 54 pillar bedded in a Don Stith stock. The trigger is set at 2 ounces and the scope is a Weaver T-36. When I bought the rifle I replaced the firing pin spring because I didn't know how old it was. I have also reworked the firing pin shape as shown below.
Here is what I did. First of all, I cleaned the inside of the bolt, the springs (old and new), firing pin etc so that everything is now dry inside. I shot 14 groups at 50 yards with both the old and the new springs and chronographed everything. Ammo used was a good lot of Eley Team listed at 1064 FPS. In the past with the firing pin, new spring and inside of the bolt lightly greased I chronographed the ammo with a spread of 34 fps and a Standard deviation of 7.8 fps.
Here are today's results , same rifle, same barrel.
Old spring Velocity spread 36 FPS STD 8.6 Group Avg .219 STD .095
New spring Velocity spread 24 FPS STD 6.0 Group Avg .190 STD .081
I did the students T test on both the velocity and the group sizes and the velocity distribution is different to the 97.2% confidence level (significant) but the difference in group size is at the 67.4% confidence level which is not statistically significant. There was one velocity that was identified as a flyer by the chronograph in the new spring group.
Interesting observations:
Velocity is definitely tighter with the new spring with no lube.
The groups look tighter with the new spring but the confidence level is not high enough so I really can't say they are different.
The velocity with the new spring but lightly lubed was almost as wide as the old spring un-lubed.
The groups were all two shot groups and the ttest was a two tailed test.
The average group size may not be impressive to many of you but they are quite acceptable to me.
The old spring is just over 1/4 inch shorter than the new one. The spring material size looks to be about the same. Other than that I can't say and I have no idea how old the old spring is.
I could visually discern no difference in the pin strike between the two springs.
All groups measured with On Target.
The velocity for the old spring was 5 fps slower than the new spring for what that is worth.
If nothing else, it looks like replacing the spring was the right thing to do and as advised it looks like keeping things inside the bolt clean and dry helps as well. I realize that keeping everything inside un-lubed may go against the average guy's intuition but it is hard to argue with the data.
I hope some find this info useful.
Jim Brossman
To that end, the discussion revolved around the firing pin spring and the lack of lubricant on the inside of the bolt. I realize this might be old hat to many of you but the experiment I performed may surprise you anyway.
The rifle I use is a 1970 Anschutz model 54 pillar bedded in a Don Stith stock. The trigger is set at 2 ounces and the scope is a Weaver T-36. When I bought the rifle I replaced the firing pin spring because I didn't know how old it was. I have also reworked the firing pin shape as shown below.
Here is what I did. First of all, I cleaned the inside of the bolt, the springs (old and new), firing pin etc so that everything is now dry inside. I shot 14 groups at 50 yards with both the old and the new springs and chronographed everything. Ammo used was a good lot of Eley Team listed at 1064 FPS. In the past with the firing pin, new spring and inside of the bolt lightly greased I chronographed the ammo with a spread of 34 fps and a Standard deviation of 7.8 fps.
Here are today's results , same rifle, same barrel.
Old spring Velocity spread 36 FPS STD 8.6 Group Avg .219 STD .095
New spring Velocity spread 24 FPS STD 6.0 Group Avg .190 STD .081
I did the students T test on both the velocity and the group sizes and the velocity distribution is different to the 97.2% confidence level (significant) but the difference in group size is at the 67.4% confidence level which is not statistically significant. There was one velocity that was identified as a flyer by the chronograph in the new spring group.
Interesting observations:
Velocity is definitely tighter with the new spring with no lube.
The groups look tighter with the new spring but the confidence level is not high enough so I really can't say they are different.
The velocity with the new spring but lightly lubed was almost as wide as the old spring un-lubed.
The groups were all two shot groups and the ttest was a two tailed test.
The average group size may not be impressive to many of you but they are quite acceptable to me.
The old spring is just over 1/4 inch shorter than the new one. The spring material size looks to be about the same. Other than that I can't say and I have no idea how old the old spring is.
I could visually discern no difference in the pin strike between the two springs.
All groups measured with On Target.
The velocity for the old spring was 5 fps slower than the new spring for what that is worth.
If nothing else, it looks like replacing the spring was the right thing to do and as advised it looks like keeping things inside the bolt clean and dry helps as well. I realize that keeping everything inside un-lubed may go against the average guy's intuition but it is hard to argue with the data.
I hope some find this info useful.
Jim Brossman
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