Tristar will tell owners of the hunting guns (which includes the Setter, Hunter, other) that they are not designed for high shot count. In my conversation with them it was suggested that a firing pin would last for about 1000 shots before some type of failure.

This is my first post and I will keep this short and try and post an image to help.
List of issues:
1) Firing pins metallurgy is incorrect:
Using soft steel does help keep the pins from breaking into pieces but it promotes rapid firing pin distortion. The distortion of the pin causes light strikes or no fires. In my experience the top firing pin will last longer than the bottom pin, reason for this to follow.
2) The firing pins use a slot and retainer pin to keep the firing pin in the proper position. The firing pin enters the receiver at a 12 degree angle due to the need to have the back of the firing pin align to the hammer. The top pin has a 12 degree slot angle matching this angle. The bottom firing pin the slot angle is zero degrees therefore the retaining pin only touches the slot at one point. This results in very high pressure on the firing pin slot. A burr more quickly develops which slows the pin down to a point that it will not reliably hit with enough force to set the primer off. This issue also occurs in the top firing pin, but since the slot has a matching retaining pin angle the effect is much slower.
3) The Metallurgy of the firing pins varies. To such a degree that (as others have noted) firing pins may have a light strike in just a few shots.
4) The hammer combined with the compression springs create an excessively high force on the firing pin. Using Newton's second and third law the firing pin will bounce back from hitting the primer with practically the same energy as when it hit the primer. Hence the damage to the firing pin slots is from the firing pin hitting the retainer pin during the bounce back. Reducing this energy to what is needed would lengthen the life of the firing pin and also reduce the trigger pull force.
5) The retaining pin is not fully in the path of the firing pin slot. This reduces the area of pin to pin contact which increases the distortion generating pressure on the firing pin. A larger pin would also increase the firing pin life.

I suggested to Tristar that firing pin distortion in the slot area means the pin is not designed correctly. They have been dealing with this issue for nearly ten years, and are quick to say there is no improved firing pins available.

In summary, I agree that the Setter S/T is a hunting gun and will last for a thousand rounds or more (or less) depending on the metallurgy of the pins in each gun built or repair parts installed. I have made a drawing of the firing pins and have sent it out to have some new ones made using "better steel". I will likely eliminate the slot switching to the slot-less design that so many other O/U shotguns use. This would result in a simpler design that can be made on one machine.

Update:
I was able to talk to Tristar customer service today. I had sent my Setter in to them for warranty repair because it had two fail to fire after the two new firing pins they sent me only lasted for 100 shots. The "engineering manager" said there must be something wrong with the receiver and he recommended sending in the gun to find out what was wrong.

He was not available to speak to me but the customer support tech read to me his service notes. The distorted firing pins were noted and the burrs were removed, there were no notes about measuring the receiver. The service tech did say that the field guns are able to be shot 200 times a year for 10 years.

I think there is only a couple of possible reasons for this problem:
1) as state in the previous posting the metallurgy of the firing pins vary to the point that some pins will distort quickly.
or
2) the receiver is promoting early firing pin failure. However, the original pins did last for around 1000 shots.

As I said before Tristar call the setter a hunting/field gun and it is not meant for high shot counts. I think I received some bad firing pins. That is why I am moving ahead with having pins made.

Second Update:
I have source a drawing of a new firing pin design. It is angular independent. The metal will be harder than OEM which hopefully will eliminate the distortion of the shape of the firing pin. The machine shop is closed to walk in traffic so we are doing all this over email.

I found in order to matched to retaining pin angle to the OEM firing pin slot material needed to be removed. Sadly there isn't enough material in the receiver to allow this. Due to the firing pin shifted farther back. This results in the pin tip not moving to the primer smoothly an occasional light strike develops.