Minimum trigger weight

[Moonshot]

Is there a minimum trigger pull weight to ensure reliable primer ignition with quality commercial .38 special ammo in a J-frame? Specifically a tuned 642 firing Federal GMM wad cutters.

Tried a search but found nothing.

[JRV]

Is there a minimum trigger pull weight to ensure reliable primer ignition with quality commercial .38 special ammo in a J-frame? Specifically a tuned 642 firing Federal GMM wad cutters.

Tried a search but found nothing.

It’s not a question of trigger pull weight. Trigger pull is affected by mainspring weight, rebound spring weight, and slop/friction in the system. Reliable detonation is a question of the hammer ignition force. You can have a heavy trigger because of excessive friction and bad tolerances/clearances and also have those same factors decrease your reliability of ignition.

You can decrease your trigger weight by lightening your rebound spring and stoning your rebound slide, and that won’t affect your hammer ignition force. That will only affect the positivity of trigger reset. Thin brass shims can be used to decrease friction on hammer and trigger bearing surfaces if those surfaces have excessive slop from the factory.

Some people have had good luck with reduced power mainsprings and extended firing pins, but nothing will give you the reliability of a heavy factory mainspring. I found the Apex Duty/Carry kit to be unreliable even with factory federal ammo in my sample size of two different 642s.

Does your 642 have an excessively heavy trigger or something (over 12 pounds)?

[Wingate's Hairbrush]

A classically trained gunsmith wouldn't go by trigger pull weight to determine reliable ignition, but by copper indent. Small copper plug placed where a primer would be, revolver dry fired pointed up. Depth of firing pin indentation into the copper would be measured to confirm it was to spec; if so, virtually all factory primers could be trusted to pop.

From race gun world, generally speaking once you get under an 8lbs double-action trigger pull you're out of the territory where you can assume any factory primer will ignite; the lower you go, the fewer will until you're basically tuning for one load, usually hand rolled. Not a recommended scenario for a defense revolver, anyway.

So far as J-frames go, not many being used for race guns for a variety of reasons, but one of them is they're harder to tune for exceptionally light trigger pulls, so except for serious wizardry, idiot coil cutting or a simply too weak mainspring, you're not at real risk to tune a J-frame out of ignition reliability (not that it can't happen).

Federals are generally considered softer primers. Personally, I don't like too light a double action trigger pull on a carry gun, and find tuning better served when it achieves smooth, linear, mechanically precise pull and solid reset.

But, put simply, around 8lbs is where you'll want to stop if you want broad reliability; even then, you'll want to put many of your chosen rounds through to determine proper working order.

What are you going for, and what methods are you using?

[Moonshot]

Wow, I had no idea this was so complicated. I guess it may be true when they say you don’t know what you don’t know.

I have a Denny Reichard tuned 642 that I am not worried about. I also picked up an old 640 no dash that may also have been tuned by Denny or else dry fired a lot - it too has a sweet trigger - somewhere around 9 1/2 lbs (I think - I don’t have a gauge).

I was asking because this subject came up in a conversation I had with a shooting buddy when he tried both my J’s. He thought any time you reduce the pull weight from factory you run the risk of light primer strikes. I countered that removing the rough edges, the grit and shaving a little off was fine, assuming someone with Denny’s skill and knowledge was doing the work. I wouldn’t try it myself. I haven’t had any issues with either of my J’s shooting anything - Federal, Speer, Winchester, even Denny’s old hand loads (this was obviously before he passed away).

[jtcarm]

As said before, there’s no telling.

If you want a better trigger, but remain confident it goes bang every time with any ammo, send it to a pro who’s experienced with S&Ws for a duty action job.

I absolutely would not tinker with springs on a carry gun.

[Wingate's Hairbrush]

...I was asking because this subject came up in a conversation I had with a shooting buddy when he tried both my J’s. He thought any time you reduce the pull weight from factory you run the risk of light primer strikes. I countered that removing the rough edges, the grit and shaving a little off was fine, assuming someone with Denny’s skill and knowledge was doing the work...Up to a point, your friend is mistaken; past that point, your friend is increasingly correct. S&W's don't leave the factory a hair above the reliable ignition threshold -- generally well-above it, such that there is room for various approaches to lightening and smoothing trigger pull, but that can go too far.

You're correct that leaving factory springs untouched but -- in an informed way -- smoothing and truing contact points can make for a lighter (or lighter feeling) trigger pull without risk of affecting ignition.