I need help with a S&W revolver

[Alaskan454]

Your primer mark at 12 o'clock looks exactly like mine when my mainspring is too light. Depending on how much resistance you have on the different internal parts I suspect that's the issue. I need to run 7.5-8 lbs to light off CCI and about 6 lbs for Federal. My first two guesses would have been primer depth or headspace assuming you aren't running a really light trigger pull. Keep in mind there's a difference between fully seated and flush primers, how are you priming these?

[bulasteve]

Is it only on one certain cylinder chamber ? Or two ? Curious.

[contender]

I have my mainspring tightened down pretty good. Almost all the way. The light strikes, are intermittent, no one chamber,, all chambers at one time or another.
In the picture,,, there are two misfires. One at 12 o'clock, & one at 6 o'clock. Notice the other 4 with definite harder strikes. The one at 6 o'clock, while a bit harder, still misfired the first time around. Both ignited on the second pass.

My primers have been depth checked, and are slightly below the case, almost exactly the same as factory ammo. (Within a thousands if not the same.)


I have noticed that, in general,, about 99% of the time,, if I have one that fails to ignite, on the second trip around,,, I can cock it in SA mode & it will fire.

I'm seriously thinking the mainspring tension is the culprit here.

[seancass]

Have you heard of or tried crushing the primers when you seat them? It's possible that your primers aren't as seated as they appear. The first "light" stike seats them a touch further and the second attempt lights off the now seated primer. It's common with some tuned guns to seat the primer very hard, to the point that the primer seater leaves a mark on the primer. Sometimes a half moon shape, sometimes a full round crushing mark.

[paul105]

Primers with light pin hits that that fired the second time (12 and 6 O'Clock in picture) are both Winchester cases -- coincidence or?? Could be rim or primer pocket (or both) diff with Win primers -- just thinking out loud here.

Paul

[contender]

I think it was just coincidence that the two shown are WW cases. I chose that moon as an example,,, but I've had issues with other brands as well.

I understand the "crushing" of the primers. As I've said,,, it happens with factory ammo, as well as my ammo. I also check my primer seating with a marble slab. No high primers here.

[bradshaw]

Contender.... I can only reply on the conceptual level, as my experience is limited to surplus DA revolvers of long ago. My impression that those WW I revolvers were made to go BANG under nasty conditions. Ever since Ruger chambered the .45 ACP in the Blackhawk that arrangement has made perfect sense.

.45 ACP was made to pretty consistent standards back when fewer outfits loaded it. 9mm Luger is, or was, a different story, with gun makers sometimes having fits trying for reliable feed from the 9x19mm Luger hither & yon across the globe. Not sure but companies loading .40 S&W may have stepped into the same boat, what with the raging popularity of the round. Whether extractor grooves are uniform across the board, I don't know. Rather expect not. Every little dimension contributes to or detracts from the whole. Manufacturers work within----or should----a tolerance package. With a rim, you headspace the revolver for a slight variation in rim thickness. With a rimless case, you have in effect two headspaces----rim and moon clip. Beside subtracting two tolerances from the reach of the firing pin, there is a third gremlin: the shucking back and forth of cartridge case in moon clip. The old revolvers had pickaxe firing pins.

A firing pin must reach deeper and hit harder to overcome the cushioning caused by variable headspacing. Would be surprised if the old time Smith & Wesson firing pin-in-hammer solved your problem. Alas, high pressure is better contained by a floating firing pin.
David Bradshaw

[needsmostuff]

May 14, 2016 9:23:29 GMT -5 contender said:

I have my mainspring tightened down pretty good. Almost all the way.

I'm seriously thinking the mainspring tension is the culprit here.

That , right there , is the number one first place to look. That screw is not an adjusting point. It is designed to be screwed down tight . Then visually verify the flat spring is pushed back all the way hard to the frame.
It has become a cheezy, common way to simulate a lighter trigger but will lead to failure. Often you can hear a twangy sound when dry fired if that screw is loose or has been shortened .
Crank that screw down and try it again.

[contender]

David,,, your thoughts of dimension differences,,, as well as tolerances that may vary did enter my thoughts. That is why I purchased & installed a longer firing pin. I immediately noticed a deeper impression on the primers that did go bang, but I still got the light strikes with the same frequency as before the swap.
One thing I haven't tried yet is a weight difference in the hammer. The hammer in my 646 is a MIM part,,, and I've wondered if a steel forged one is heavier. I have some old hammers with the floating firing pin,,, but not one of the newer forged ones that are used in the floating firing pin models to see if there is a weight difference. My MIM hammer is scalloped on it's sides,,, so that made me consider the possibility of a hammer weight issue.
A combination of the hammer weight, followed by the mainspring not quite heavy enough, with the looser tolerances of a moon-clipped gun,,, may align up to where I'm getting these issues intermittently. With the rounds igniting when I go into SA mode,, makes me really consider it more.
I've been working too much to allow me to try a few things, but I have plans to try a few more things before I ship it back.
As always,,, I try & eliminate as many possibilities as I can before I give in & let someone else have a go at it.
Thanks for your thoughts!

[needsmostuff]

May 11, 2016 11:01:19 GMT -5 contender said:

I may shave a few thousands off the mainspring screw as well,,, if other solutions don't work.

This will make the problem worse. If this has been done before get a new screw or shim something between the screw ( I have seen spent primer cups used ) and the spring to bottom that spring against the frame.

Inadequate tightness of that Screw/mainspring WILL display every symptom you report.

[contender]

Good catch! I was thinking backwards,,,,!
I may actually add a shim between the screw & spring,,,, vs shaving the screw. However, I may have been thinking about cutting off some of the screw head,,, giving me a deeper set to the screw.

[bradshaw]

Contender.... A MIM part may weigh the same or close to a drop forged or investment cast part. A skeletonized part by any method intends to reduce weight. I won't have "game" parts in my working guns. As to reliability, I do not distinguish between carry, hunting, plain old marksmanship, and competition. Thus, while others put titanium or aluminum firing pins in their XP-100 Unlimited pistols, mine were dressing with the Remington steel firing pin.

As a footnote, just did a trigger job on a new Ruger 10/22. The hammer appears to be die cast or MIM. However made, it is file hard. Had to grind, then dress with diamond "stone" and white ceramic.
David Bradshaw

[seancass]

It is also possible to add tension to the spring by bending it.

[pbcaster45]

I would have suggested Federal Small Pistol Primers but I can't remember the last time I saw ANY for sale! Practically unobtanium!

I've had light primer hits with Winchester Small Pistol Primers in my PPC Revolver, each was caused by me allowing my thumb to drag on the hammer. Big hands...

[tek4260]

How much headspace do you have on each chamber? Load a moon clip with empties and check each chamber by sliding a feeler gauge between the rim and the breech face. It shouldn't be an issue, but it could. Also add a primer cup to the end of the tension screw and see it that helps. I had to do it on a 625JM.