Failed ignition after parts change?

[ihocky2]

Hey guys, I was having a problem on my 625 with my cylinder binding up and narrowed it down to a bent extractor rod and center pin. Since everyone has them on back order I swapped out the extractor rod, center pin, and extractor collar with the ones from my 657. While I had everything opened up I installed a Power Custom extended firing pin. Yesterday I went to the range to function test; click, click, click. So I kept tightening the strain screw until I finally got it to go bang, it was fully tightened. Before the parts swap and the new firing pin I had it running 100% ignition at 6-1/2 pounds.

What are the chances that the extended firing pin it not working?

My other thought was, did the cylinder parts change the head spacing? The center pin and extractor rod should have nothing to do with head spacing. Would the extractor collar make enough of a difference to through the ignition that far off? At anything under full tension I get 50% ignition on a good cylinder full, even at only ¼ turn backed off.

[Carmoney]

Sounds like it's the firing in. None of that other stuff would affect ignition.

I'm not familiar with the Power Custom extended firing pin, but it sounds like it might be counter-productive.

[ihocky2]

When I go to the range again this weekend I'll have to post a comparison picture of the firing pins. The nose of the pin is the same length at the factory, the extra material is in the length of the firing pin body with the slot for the retention pin cut longer to the rear.

[bountyhunter]

Check the cylinder for end shake. Measure barrel to cylinder gap with the cylinder pushed forward and pulled back. If the end shake is more than about .001", it can affect ignition as the cylinder moves when the round is struck which absorbs a small bit of the hammers energy. Since you are clearly dialing down for lightest trigger pull, that can change your ignition.

As for extended firing pins: I tested them and found they did not improve ignition on my guns compared to a proper SW firing pin (length .495" as I recall). There were some defective SW pins made but a proper one will work just fine. Some of the aftermarket pins drag in the firing pin channel, make sure yours slides freely. They are also prone to breaking.

Edited May 21, 2014 by bountyhunter

[bountyhunter]

When I go to the range again this weekend I'll have to post a comparison picture of the firing pins. The nose of the pin is the same length at the factory, the extra material is in the length of the firing pin body with the slot for the retention pin cut longer to the rear.

Then I wonder how the pin could work any different than stock. Unless it is reduced mass like titanium to get more velocity? Bottom line, the bullet's primer stops the forward motion of the firing pin so as long as it has enough forward travel range to fully dent the primer, anything more than that is never going to be used.

[Tom E]

So put the old pin back in and see if it goes back to working. The S&W titanium pins (make sure it's a long one) do seem to be best.

[ihocky2]

So a slight update. I went to the range this weekend and put the factory firing pin back in with minor improvement. I am still fairly heavy for the trigger weight but lighter than had been and getting more consistent strikes, but still only 4 or 5 out of 6. My plan tonight is to check the end shake with the extractor collar from my 657 in it and try it with the original extractor collar. Neither of those should make a difference, but since it is a part I changed I might as well check it out.

I am really hoping it is an end shake issue because after that I am out of ideas. I was sitting around 6.5 pounds before I did my polishing work and now have to be back to almost 9 pounds, I haven't put the pull gauge on it yet. I will also check the weight to pull the hammer as it is currently set just for reference.

[ihocky2]

After a few minutes with the feeler gauge I think I have found an end shake problem. I have between .004" and .005" of end shake. Cylinder gap is .008". It didn't matter which extractor collar was in, which it shouldn't.

I tried checking the hammer pull weight and I am not sure if I did it right. I tried pulling the hammer back and got 3-1/2 pounds and I tried letting the hammer fall on the trigger scale and got 1/2 pound. Is this about right or did I do it wrong.

I am going to order a few end shake bearings and hope that clears everything up. I went with the extended firing pin originally because I could not get the trigger pull as light as some of my other guns. Now I am betting it was the end shake that I uncovered. Though why it was lighter before than it is now I am puzzled about.

[bountyhunter]

You may need to reface the inside of the cylinder where the end of the crane tube rubs on it as it may have worn a groove into the inside surface of the cylinder. Why that matters is the end shake washers match the outside of the crane tube but not the inside edge which means the washers don't fit into the groove cut into the metal and will cause it to bind up.