I have a Smith mod 66-3 that just has weak primer hits.Sent it back to Smith once and they say every thing is A- OK.Using reloads or factory ,38 or .357 it is a crap shoot if it will work.The same ammo is flaw less in my Smith 686.Waiting to hear back from Smith on the issue.Anybody have a clue with this soon to be pry bar ? Thanks

Is your mainspring tension screw nice and tight?

OK ,So where the *&%$ , or what the main spring screw  is for ,and where is it located,and what is it for ????  Thanks for all the help . I will give it a look at...

Being I can't tell if you are being a smart-ass or just can't create a sentence FOR SHIT--I will give you the benefit of the doubt and respond.
The mainspring tension screw, also called a strain screw, well, it tensions the mainspring, which in turn creates the force necessary for the hammer (its striking power). If its loose, not enough tension--therefore light hammer strikes.
It is located on the gripframe, towards the bottom, front (triggerguard side).
If you have wood target grips or rubber Uncle Mikes, Pachmeyr or similar, you will have to remove them to see it and tighten it. If you have wood service grips it will be exposed.

OK,so I aint no good at grammer and what ever else ,I checked the spring under the grips that is on the front part of the frame and it is tight.Smith e mailed  and says to send it back ,BLAH BLAH BLAH.Thanks for the spring thing info.Good thing you dont work at the Motor Vehicle place .People coming through there are a whole lot stupider than I am .

Quoted: OK,so I aint no good at grammer and what ever else ,I checked the spring under the grips that is on the front part of the frame and it is tight.Smith e mailed  and says to send it back ,BLAH BLAH BLAH.Thanks for the spring thing info.Good thing you dont work at the Motor Vehicle place .People coming through there are a whole lot stupider than I am .

....Yeah, please send it to Smith & Wesson.