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Old 03-21-2013, 04:08 PM
Skunkhome Skunkhome is offline
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Default Light primer strike, aftermarket main spring

Yesterday I went to the range and squeezed off approximately 70 rounds just to get familiar with my "new" 620. The revolver shot beautifully with one small exception. One of my reloads failed to fire. I had noticed that the firing pin strikes were much lighter than what I was used to with my model 10 but thought little of it until I had the misfire. I ran the round through three times and it appeared dead as could be. I squirreled the round away and went back to shooting without rurther failure.
I was wondering if I had my first misfire due to a bad primer in 45 years of reloading. The thought bothered me as I have grown to trust my reloads without question. When I got home I pulled the bullet and this morning after the wife left I shoved the primed case into my mod 10 and it fired perfectly.

If you look at the top group of cases you can see that the primer strikes are light with exception of the nickel case with brass primer and the brass case directly beside it that was fired in my model 10.
I took the revolver back to the dealer where I bought it and they opened up the gun and found a aftermarket main spring in the revolver.
At my request the smith replaced the mainspring with an OEM spring. The group of cases at the bottom are the mixed lot of rounds they ran through the pistol. The primer strike is noticeably heavier but I have tried dry firing it and the trigger is just as nice as it was before. We will see how she does. Regardless the shop warrants all their used guns for 1 year from date of purchase.

Last edited by Skunkhome; 03-22-2013 at 09:15 AM. Reason: Re-title
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Old 08-02-2013, 03:40 PM
ChazFraz ChazFraz is offline
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I get the same exact problem with my Model 10-11. I get over 40% failed to fire. The hammer doesn't seem to hit hard enough to spark the primer.

Maybe a new mainspring will help.
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Old 08-02-2013, 04:00 PM
jdickson397 jdickson397 is offline
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I have used the high quality Wolff aftermarket "reduced power" mainsprings with some success but often they will not fire hard primers such as Winchester or CCI. For that reason competition shooters who want a light trigger pull switch to Federal primers for their reloads. I did the same and that solved the problem.
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Old 08-02-2013, 04:27 PM
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Naples22 Naples22 is offline
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My experience is that reduced power springs seem to cause this problem. Ive had it happen a few times with both factory ammo, and my own reloads. Every time they fired in a gun with factory springs.
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Old 08-02-2013, 11:34 PM
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Alk8944 Alk8944 is online now
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One thing most people do not consider is that not only do reduced power mainsprings sometimes result in mis-fires, they also affect consistency of ignition. Most believe that a primer either fires or it doesn't, this is not true. The kinetic energy with which the primer is struck has an effect on the energy released by the primer and consequently the quality of ignition of the propellant charge. Not only will mis-fires result, but also squibs.

If you don't believe this, and you have a chronograph, try this. Load a batch of ammunition which you know is close to full-power for the cartridge. Using a S&W revolver with a standard mainspring that hasn't been tinkered with.

First, shoot enough rounds to ba a statistically significant sample, at least 20, and record the results, average, extreme spread and standard deviation.

Back out the strain screw 1 turn and fire another 20 and record the results. Repeat until you start getting mis-fires.

Finally, compare results of each string. If all were done the same day, under the same conditions, you will see that as firing pin/hammer energy is reduced that average velocity will also go down, while the extreme spreads and standard deviations increase.

Believe it or not, the old saw about a gun shooting "faster" the harder the hammer strikes the cartridge really does have a basis in fact! Up to a point of course.

Do you really want to trust your life to a gun with a light mainspring just because the trigger pull is a pound or so lighter?
Gunsmithing S&W since 1961
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Old 08-03-2013, 12:35 AM
Boge Boge is offline
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Originally Posted by Alk8944 View Post
One thing most people do not consider is that not only do reduced power mainsprings sometimes result in mis-fires, they also affect consistency of ignition....

Do you really want to trust your life to a gun with a light mainspring just because the trigger pull is a pound or so lighter?

Winner, winner chicken dinner!!
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