Here is my problem.
I have a Marlin model #"512 Slug Master" in 12 gauge 3" magnum that while at my last range session had three sabot slugs from two different manufacturers fail to go off when I pulled the trigger. This is the first time anything like this has ever happened to any of my firearms, so I have zero experience in trouble shooting for it. Up to now this gun has been 100% reliable and has performed superbly and is a tac driver to boot. Granted the 512 is no M70 or M700, but my 512 shoots 100% as well as my A-Bolt slug gun and serves its perpose of design extreamly IMHO.

Considering this slug gun in well over 14 years old and had had something like 500 to 600 sabot slugs fired out of it, I figured it was simply a case of the fireing pin or some related part simply showing signs of were. I promptly ordered the replacement parts I felt I would need along with a schematic of the 512 Slug Master from the good folks at Numrich Gun Parts.

When I received the parts in the mail I proceded to disasemble the bolt of my 512 and give all the parts a compleat cleaning, although they were surprisingly clean. I also gave the new replacement parts a cleaning as well.

I then compaired the three parts that make up the old firing pin firing pin assembly, thay are #1-the firing pin itself, #2-the firing pin spring guide, and #3-the firing pin spring, the same three new parts I bought from Numrich gun parts. After as through and compleate an comparative inspection as I could make, including measuring both with my calipers, I could find no significant differences, obvious part failures or obvious signs of wear. I will also add the parts that make up the entire bolt assembly are very stout.

After I had assembled the bolt and was trying to see if there were any differences I could find is when I discovered this. Much to my surprise you can work the bolt handel back and forth through its race or where on the front section of the breach bolt it travels around on to be able to cycle the bolt and operate the gun. When I did this while observing what happened I could see that the part of the firing pin that protrudes past the bolt face would decreese signifacantly while doing so. It then dawned on me that once while hunting over 10 years ago, I went to shoot a deer only to have nothing happen when I squezed the trigger. I instantly recycled the bolt and the 512 Slug Master went off and I took the deer. I immediately placed the bolt back into the receiver and found I could cycle the bolt more than far enough up to cause a miss fire and the rifle would still fire, even though the firing pin would not protrude out far enough to couse the primer to go off.

As A result of this startaling discovery on my part I am now wondering that if this is my problem and not anything to do with my firing pin assembly, as it may be working perfectly.

So my question is this:
Does anyone out there know of a safe and reliable whay to check to see if a firing pin once you fire the rifle, is functioning properly and is striking the primer when fired, to the proper depth to ensure consistant primer detination? I ask as because one, I do not know of ANY gunsmith that lives anywhere near me and second, my range is 81 miles from my house. I am fervently hoping that my problem was simply a case of not having my bolt compleatly closed, but I wont know for sure untill I can test to see if the firing pin is working ok. It may be that firing is my only option. The only test option for home or range I can think of it to cannibalize a dozen or so of my cheep upland game shells in 12ga by opening them up, removing the shot, wad, and powder and using them to test fire in my 512. Although I bought my sabot slugs in bulk while on sale, at over $2.00 a shot relpacement cost, thay are a tad pricy for testing purposes.

Well now you all know my situation, what do you suggest I do?

Thanks to any and all who help me out on this.
Sincerely,
Arthur.

You may be starting to get excess headspace from wear on the locking surfaces of the bolt. Cutting apart the cheapo loads is a good idea for testing. You can also deprime a fired case, and fill the primer hole with modeling clay. When you chamber this and pull the trigger, it should give you an impression of how much the pin protrudes. Also sounds like your bolt handle was not all the way down when it misfired--this is operator error, and is a safety feature to keep the bolt out of your brain when firing!