Question about firing pin strikes


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Gottahaveone
October 11, 2010, 08:42 PM
I have a Taurus 885UL that has one of the stoutest trigger pulls that I've ever personally seen. I went to the Wolff site and they show the 11lb spring as stock, and the 9lb spring as "light". I ordered the 9lb spring and installed it. Based on the new trigger pull, if the Wolff spring really is 9lbs then the factory one must have been at least 20.

The trigger pull is greatly improved, to the point that I don't get finger cramps when shooting it now. However, one chamber out of the five misfires due to light pin strike about every other cylinder full. The other four have a nice deep indentation but the one (always the same one) has a really light dimple even when it does fire. I have rotated the cylinder and looked at the gap between the cylinder and breech face and if it changes for that one chamber, it's such a small amount that I can't see it with the naked eye.

To rule out variations in brass rim thickness with all the "thin" rims coincidentally going into that one chamber, I've taken the cartridge from the chamber that didn't fire and moved it to another one and it fires with a deep indentation. I'm at a loss to explain it. It should either have a good healthy dent on all five, or it should have a light strike on all five.

I've ordered the 11lb Wolff spring and hope this will cure it and still give me a trigger pull that I can live with, but I would be grateful if anybody could offer an explanation as to why it's only doing this on the one chamber.

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Dave_in_Fairview_Park
October 12, 2010, 03:21 AM
Check the one chamber on the cylinder,that may be the problem not the pin.

Had the same problem on a old S&W -one chamber was a bit oval,it had a light pin hit and did not hand eject the shell on the same chamber.

Powerglide
October 12, 2010, 05:50 AM
Well, not to slam but I've never owned a taurus that wasn't problem prone.

Gottahaveone
October 12, 2010, 04:51 PM
Well, not to slam but I've never owned a taurus that wasn't problem prone.

Thanks, THAT was helpful. I almost didn't list the manufacturer because I knew sure as hell somebody would show up with a comment like that no matter who I said made it. Being inevitable doesn't make it any less annoying :scrutiny:

Check the one chamber on the cylinder,that may be the problem not the pin

That was my thinking too. I have looked closely at the chamber and measured both the chamber and the fired brass as thoroughly as a set of Mitutoyo calipers will allow and can't find any variances.

If I can get my GF to temporarily return my older 85UL that she absconded with, I'll swap that hammer spring in and see what happens. I'm hoping the 885 will work consistently with the 85 spring and the 85 will work with the lighter Wolff spring. I don't think there is anything "wrong" with the 885, I'm just confused as to why it only has light strikes on just the one chamber with the light replacement spring. It runs fine with the heavy factory spring, it's just got a brutal DA pull.

rcmodel
October 12, 2010, 04:56 PM
The only possible reason it only misfires on one specific chamber is excess headspace on that chamber.

Get yourself some Scotch Magic frosted tape.

One thickness is about .002" thick.

See how many layers will fit on the head of a round and still allow the cylinder to rotate.

Then try the same on the one that misfires and see if it takes more layers of tape to tie up the cylinder.

If so, that chamber is bored too deep if it has counter-sunk case rims.
Or the cylinder is not straight & square on the back if it doesn't.

In either case however, the cylinder is defective.

rc

Gottahaveone
October 12, 2010, 08:11 PM
RC,
Now that's an excellent idea. Instead of using tape, I took a piece of thin register receipt paper and after sizing/decapping a piece of brass, I folded the paper into a "feeler gauge" that would just slip out with minimal force on the "good" chambers. Then I tried it on the "bad" chamber. My fingers aren't calibrated strain gauges, but the force to pull the paper shim out was, as best as I could judge, equal to the other four "good" ones.

I'm at a loss to explain this one. Because it works consistently with the factory spring, I'm going to put that one back in and wait to see what happens when the "factory standard" 11lb Wolff arrives. I hope to get reliable ignition and a better pull. If not, I'll leave the factory one in it because reliable ignition ALWAYS trumps trigger pull quality.....

Old Fuff
October 12, 2010, 11:31 PM
When a cartridge fires the primer fire-forms around the tip of the firing pin, and that leaves the deep indention. When the cartridge doesn't fire then the primer only shows the firing pin's dent.

The Taurus uses a transfer bar safety system, where the hammer hits the transfer bar, which in turn hits the firing pin, which then hits the primer. During each step some energy is lost, and your replacement spring may be borderline. You may have a thin transfer bar, and changing it might solve your problem.

Annother possibility is to place a small washer on the mainspring strut between the spring and retainer.

And yes, the factory spring is heavy to insure absolute reliability.

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