I was shooting my model 637 double action and started gettin ftf. The primers on the rounds that didnt fire were lightly dented. I had one out of every 5 rounds fail to fire. I tried the rounds that didnt fire a second time and they fired. It would only do it when firing double action. Any ideas? The gun is only a year old and hasnt been fired much.

it could be the spring itself, wolf springs are the most reliable

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Where is that screw located

there is not a screw on a 637, it uses coil mainspring, if you are shooting reloads they could have hard primers. if you have the problem with factory ammo, you will need a stonger mainspring, s&w would fix it but it is a lot of trouble sending it back for something like that, it can be replaced for a few dollars.

I tried two different brands of factory ammo and they both did it when firing double action. Are you saying the spring is just defective because it hasnt been shot enough to be worn out.

no, the spring will not wear out for lack of use, but sometimes the springs are just to weak. any friction can rob the power from the spring as in custom grips that rub on the mainspring, or lack of lubrication.

thanks, for the help, I may just send it to s&w and let them take care of it.