Colt "357" Light Strikes in Double Action

[Rio Laxas]

I have a Colt "357" which has been giving me trouble with light strikes in double action. It locks up tight with no end shake or side play and it does fine in single action. I replaced the mainspring and it seemed to do better for 20 rounds or so, but now the problem is back.

I read a post on another forum where Grant Cunningham stated that it was not unheard to find Pythons with "slightly excess headspacing and slightly short firing pin protrusion from the factory."

Is there anything else I should check out?

 

[rcmodel]

Could be your ammo case rim thickness.

Have you tried different ammo?
See this about that:

http://www.thehighroad.org/showthread.php?t=563715&highlight=colt+commando

rc

 

[Rio Laxas]

Wow, I did not know that!

I think I've used a couple of different brands in it, but I will pay more attention and try several.

 

[Glen]

I am a reloader and I was getting what appeared to be light strikes in my new GP-100. Turns out that I was not seating my primers deep enough.

 

[Jim K]

Many gunsmiths, both in the factory and outside, have tried to give the Python a super easy DA trigger pull. The result is often a mainspring that is not tuned properly or is simply too light. After ruling out ammo (dead primers, and improperly seated primers) and headspace, I would install a new mainspring. If it makes the pull slightly heavier, you have a choice, a light pull followed by a click, or a heavier pull followed by a bang.

Jim

 

[dfariswheel]

Misfiring in double action is a classic symptom of a mainspring that's been bent to lighten the trigger pull and bent too much.
While bending the spring IS a valid pistolsmith technique on the old type Colt action, the reason for problems is that the job is done blind, without using a trigger gage.

The bend is done by installing a small diameter rod between the rear of the two "legs" of the spring and cocking the hammer to put a slight downward bend in the upper leg of the spring.
If that's not enough lightening, a slightly larger pin is used.
People get in trouble because they start out with too large a pin and have no idea what the weight of the trigger is because they didn't use a gage.
result is too light spring tension and misfires in DA, if not in SA too.

You can sometimes ID a "tuned" spring by a slight downward bend in the upper leg of the spring.

One aid in diagnosing your 357 problem is to use a trigger gage to weigh the double action and single action pull.
The "I" frame 357 and Python are the same action so measurements are valid for both.

Double action....Maximum...12 pounds.
No minimum.

Single action...Maximum...4.5 pounds.
Single action...Minimum...2.5 pounds.

Note that single action and double action are both affected by the mainspring. Lighten one and you lighten the other.

Inspect the firing pin for chips or breaks. Happily the 357/Python firing pin is easily changed by removing the rear sight and sliding the cover plate up.
Check the pin and spring tension for fouled parts. If necessary disassemble and clean the pin and spring and the seat in the frame.

NOTE: On most all Colt schematics for the 357 and Python the firing pin is shown BACKWARD.
Years ago a technical artist mistakenly drew it backward and everyone just reuses the same view.
To be clear, the cone shaped firing pin spring small end fits over the firing pin with the wide open end facing the muzzle.

Best advice is to try some different ammo. If it still misfires, replace the mainspring with a new spring.
Most new springs sold today are actually non-Colt replicas but are factory equivalent.

If none of this cures the issue, I strongly recommend you NOT take it to any local gunsmith.
Very few these days are qualified to work on the old Colt action and often you get a gun back even more botched up.
If repairs are needed, send it in to Colt, or to Frank Glenn Gunsmithing in Arizona.
Colt is the go-to preference, but Glenn is a famous Master who does Colt factory level work.

 

[243winxb]

mainspring test

A test for a Smith and Wesson revolver, model 28, 357mag., may work on other guns also<> Gun empty.*
Dryfire gun and hold trigger fully to rear.
Cock hammer with thumb.
Hook a weight around the hammer (for example 3 1/2 LB minimum weight for 357).
The hammer must not move rearward when the gun is lifted.
The hammer should lift 3 1/2 lbs without going into the cocked position.

 

[Walkalong]

My Colt OMM .38 Spl will not always set primers off in DA. Might be the same thing. I have no other revolvers that do this, Colt or S&W.

 

[Rio Laxas]

Just to clarify....I did replace the mainspring with a new one from Numrich prior to shooting yesterday, but the problem persists.

If none of this cures the issue, I strongly recommend you NOT take it to any local gunsmith.
Very few these days are qualified to work on the old Colt action and often you get a gun back even more botched up.
If repairs are needed, send it in to Colt, or to Frank Glenn Gunsmithing in Arizona.
Colt is the go-to preference, but Glenn is a famous Master who does Colt factory level work.

I'm glad to hear another recommendation for Frank Glenn. I knew that Grant Cunnigham was no longer gunsmithing, but I went to his web page to see if he recommended anyone and it was Frank. I've got a different Colt "357" that could use a tuneup, but hopefully I can troubleshoot this one on my own.

One aid in diagnosing your 357 problem is to use a trigger gage to weigh the double action and single action pull.
The "I" frame 357 and Python are the same action so measurements are valid for both.

Sweet, an excuse to use my seldom used trigger gauge. I'm getting 3 lbs 11-14 oz in single action and 10lbs 12 oz to 11 lbs 01 oz in DA with the new spring.

 

[Driftwood Johnson]

Howdy

All double action revolvers have a slightly lighter double action hammer strike than single action hammer strike. This is because in double action mode the hammer falls earlier than in single action mode. Work the action and you will see this. Since the hammer falls earlier in double action, the main spring has not been compressed as much when the hammer falls.

So you may be right on the edge where your single action hammer strike reliably sets off primers and your double action strike does not.

If you are using reloaded ammo, be sure your primers are properly set. Primers that are too high absorb some of the hammer strike as they move deeper when they are struck.

If the problem happens with factory ammo, the hammer spring is probably too light.

 

[Jim K]

Is this a new (to you) gun or has it just started acting up? If it has been fine up to now, you can ignore the following. But if it has always (in your possession) had a problem there are a couple of other things to check, like a problem in the hammer block mechanism, a problem with the fitting of the rebound lever, a de-horned hammer without enough mass, or a short firing pin.

Jim

 

[Pudge]

I had a GP 100 that was giving light strikes in double action. I changed springs, same issue. Had a gunsmith look it over and he found something under one edge of the transfer bar. He wasn't confident that it was significant at all. No more issue however. I had torn it down and cleaned it, but apparently not enough. Probably not your problem, but worth checking, and a nice no dollar fix if it is.

 

[dfariswheel]

Sweet, an excuse to use my seldom used trigger gauge. I'm getting 3 lbs 11-14 oz in single action and 10lbs 12 oz to 11 lbs 01 oz in DA with the new spring.

In that case, your next stop is to inspect the firing pin and spring.
As above, you need to remove the rear sight from the frame then slide the retaining plate upward.

A trick to get the rear sight back on without changing the zero is to use an automotive feeler gage to gage the gap between the bottom of the sight base and the frame.
When reinstalling the sight, just crank it down until it spaces on the feeler gage.

To remove the rear sight, unscrew the elevation screw until it disengages from the frame, then use a 1/16" pin punch to push the sight retainer pin out.

Again, make sure the firing pin spring is on the right way around with the small end over the firing pin.
Make sure the correct firing pin and spring are in there. I've seen these replaced with non-correct parts.

If you have a firing pin protrusion measuring device OR you can come up with another method, with the hammer pressed firmly forward and the firing pin all the way forward it should protrude from the face of the frame by 0.042" Minimum and 0.056" Maximum.

If this is all okay, I'm going to recommend sending it in to Colt.
Glenn is down until after the first of the year.

 

[Gordon]

Thank you so much dfariswheel !

 

[Rio Laxas]

Thank you for all of the suggestions. I will check it out again this weekend and act accordingly.