S&W 15-2 firing pin problem

[4D5]

I am having problems with my 15-2 firing pin. I have occasional light primer strikes and subsequently failure to fire.

I did some checking and found that the nose of the firing pin is striking the top of the frame in the hammer slot. I think this is where I’m getting the occasional light primer strike.

I checked the firing pin and it floats freely in the slot in the hammer, however the firing pin is not retained in the down position by a spring (or it appears so)

My question is… you guys with 15-2 revolvers, is the firing pin on your 15-2 retained in the down position by spring pressure?

I called S&W earlier and the rep said that not all firing pins have springs.

This is a link to my post on my 15-2 in question.

http://thefiringline.com/forums/showthread.php?t=389625

I’d appreciate any feedback from 15-2 owners.

Thanks, 4D5

[BillCA]

4D5,

My first thought on light-strikes is to always verify the mainspring screw on the front of the grip frame in tightened. It should be all the way in and slightly snug. Some folks back off this screw to lighten the trigger pull. But this can result in misfires.

I just checked my 4-in 15-3 and glory-be... no firing pin spring. Color me surprised.

How did you surmise that the FP is striking the top of the hammer slot, if I may ask?

[4D5]

BillCA,

In checking I found that I can cock the hammer, and hold the firing pin in an upward position, lower the hammer and see that the nose of the firing pin contacts the inside of the top of the hammer slot.

Visual inspection confirms as there is a shiny line in the location described.

There is not end shake and headspace is good plus fired rounds have good deep strikes.

Strain screw was and is down tight in the frame.

4D5

[madcratebuilder]

My question is… you guys with 15-2 revolvers, is the firing pin on your 15-2 retained in the down position by spring pressure?

Neither my 15-2 or 15-3 has a spring assist firing pin. The firing pin is free to pivot a small amount and gravity keeps it in the down position. Maybe you have a build up of powder residue, try cleaning it with some brake clean or other spray cleaner then lightly lube it with some Eezox or other lube that dries.

[earlthegoat2]

My -2 has no firing pin spring either.

[Malamute]

It may be worth trying a new mainspring. Some gunsmiths and kitchen table copycats tweek the mainspring, so the screw being down tight doesnt completely rule out the spring tension as an issue. If you have another Smith, swap springs and see if the other gun then has problems, and see if your 15 still does. Could do that with a buddies Smith also just to see if thats a problem.


I believe a mainspring is about $8-$12.

[carguychris]

It may be worth trying a new mainspring. Some gunsmiths and kitchen table copycats tweek the mainspring, so the screw being down tight doesnt completely rule out the spring tension as an issue. If you have another Smith, swap springs and see if the other gun then has problems, and see if your 15 still does.

+1. FWIW some mainsprings have problems even if they haven't been modified; they will "take a set" and lose their "springiness" simply from being held in the installed, arched position for decades. A new factory mainspring that's not installed in a gun will only be arched in the top ~3/4" below the fork. If the entire thing is arched, clamp the bottom of the spring in a bench vise and gently bend the remainder of the spring until it's more or less straight. This is sometimes enough to cure light strikes.

Another potential cause is that the strain screw has been filed down, or a former owner has installed a RB strain screw, which is ~0.10" shorter than a SB screw. Shortening the screw has the same effects as backing it out- both good and bad- but it can't be undone without a replacement screw.

I don't have a strain screw and a caliper handy, but a quick search of the S&W forum reveals that the correct length for an older (pre-1980s) SB strain screw should be 0.61" measured over the screw head. (I'll double-check this against my M15-3 later.) New replacement strain screws are longer and will need to be filed to length.

Another popular option is to replace the strain screw with a 1/2"-long 8-32 thread Allen-head set screw, generally available at your friendly local Lowe's home improvement center. This will essentially make your trigger pull adjustable and allow you to "tune" the gun to the primers you're using. The only catch is that it's not a great idea for a defensive revolver because the set screw could potentially shoot loose and cause a light strike at the worst possible moment. You can Loctite it in place, but this will make the revolver hard to disassemble for maintenance.

[4D5]

The strain screw is/was tight and the mainspring appears to be unaltered.

I'm suspecting something else is going on because for the fired cases there is a very substantial firing pin dent, so that would indicate that there's something intermittent going on. Otherwise, all the cases would have light strikes. My current suspicion is that the hammer block may not be dropping completely and causing partial interference.

[carguychris]

I don't have a strain screw and a caliper handy, but a quick search of the S&W forum reveals that the correct length for an older (pre-1980s) SB strain screw should be 0.61" measured over the screw head. (I'll double-check this against my M15-3 later.)

I checked it and it measures 0.578" over the screw head. Go figure.

...the mainspring appears to be unaltered.

It could be aftermarket.

I'm suspecting something else is going on because for the fired cases there is a very substantial firing pin dent...

Fired cases will always have a substantial firing pin dent because the expanding hot gases forcefully drive the primer backwards into the firing pin bushing when the round fires.

My current suspicion is that the hammer block may not be dropping completely and causing partial interference.

There's almost no way for that to happen because the mechanism is stone-simple and pretty much failsafe. An angled slot on the bottom of the hammer block engages a pin on the rebound slide. The hammer block rides in a slot in the sideplate. As the rebound slide moves back and forth, the pin moves along the angled hammer block slot, causing the hammer block to move up and down in the sideplate slot. The parts fit so loosely that it's virtually impossible for them to wear against each other; in fact, the hammer block is so loose that you can hear it rattle if you shake the gun, prompting the occassional "*** why does my brand-new {insert model number} rattle when I shake it?!?" post on this forum.

FWIW you can observe the top of the hammer block if you cock the revolver SA and look into the hammer slot; the top of the hammer block should be below the firing pin recess.

I have never heard of an intermittent failure to fire being caused by the hammer block. Trust me, culprit #1 is the mainspring, culprit #2 is the strain screw, culprit #3 is a worn or damaged firing pin. #1 and #2 are cheap and easy to replace. As the mechanic's saying goes, if you see road apples, don't go looking for unicorns until you're sure there are no ponies.

[James K]

The hammer-mounted firing pin striking the top of its slot is normal. I suggest the problem may be ammunition. As carguychris says, the fired primers have flowed back around the firing pin and look "normal", while the primers that did not fire seem to have shallow dents. If the unfired primers show the center of the primer depressed rather than just a shallow round mark, the ammunition is likely faulty.

Jim

[4D5]

First of all, thanks everyone for your input.

I finally had a chance to check closer. Well sure enough a kitchen gun plumber shortened the strain screw, it has a flat shiny tip

The main spring appears to be dorked with too It’s shiny all over and has been thinned on the sides. It doesn’t look anything like a factory original.

I checked the barrel/cylinder gap and it’s right at .006 and the brass to recoil shield is right at .008.

I’ll be calling S&W tomorrow to order replacement parts.

Thanks again everyone for your assistance and input.

4D5