Monday, December 29, 2014

A simple firing pin gauge

Whats a good method to measure the firing pin stick out as it relates to the breach face? 
I've been working on some  H&R Pardner shotguns and Handi rifles lately trying to track down the source of misfires and other such failures to perform as designed. The first hypothesis of the problem was presumed light firing pin strikes, possibly caused by short firing pin protrusion. Although this has turned out not to be the case with the two Handi rifles I am working on currently both rifles had shorter than minimum firing pin protrusion to be reliable. Having tried to measure the firing pins accurately proved a bit of a challenge as I was using the depth measurement on a dial caliper to try and get a measurement, this quickly proved inaccurate as one must hold the trigger to the rear while at the same time taking the measurement keeping the instrument perpendicular to the breach face. I knew there must be a quicker, easier and more accurate way to get the measurement I was looking for...and there was. Brownells sells a marvelous little tool that is comprised of 3 parts and costs $30. Yes, $ that wasn't going to happen any time soon. I happened to have a good stock of 0-1 in the shop so I set to work making a rough copy of the brownells firing pin protrusion gauge. Yes they make and source excellent tools but I wasn't going to pay $30 for something so easy to make myself.

The actual making of the tool will not be pictured here as it is fairly straight forward.
Materials include:
1/2" drill rod
1/4" drill rod
1/4" drill bit
Socket head set screw of your choice with offending tap and drill.
Lathe and necessary accouterments for the proper use thereof.

Taking your 1/2" drill rod, drill a 1/4" hole about 1" deep, take cutoff blade and part so you have a piece about 3/4" long or so, this dimension is not critical but do make sure both ends are faced. Deburr drilled hole as needed.. About 1/4" or so from one end drill and tap a hole into the side of the cylinder for your set screw.

Take your 1/4" drill rod and accurately measure and cut off a 1.000" piece making sure both ends are faced. It really can be any length you want it to be so long as its longer than the 1/2" stub you made earlier. It would save you time and math in the future though if you just took your time and made it a accurate 1.000" long.

The best things are simple, I made two of these gauges in about 45 minutes.

Tip- if you know you will be using this gauge on bolts with recessed faces it would be a great idea to turn the end farthest from the set screw hold down so it can sit inside what you think will be the smallest case head you might work with would be.

This is one possible method to measure the stick out, lets see how it works. (Photo by CP)

Might look good side to side but what you can not tell is the instrument is badly tipped causing the reading to be misleading. (Photo by CP)

Here is our gauge in action, simply tighten the set screw and take measurement with the same dial calipers from before. Don't forget to subtract the 1.000".....

Small yet critical
Simple tools like this make quick jobs of measuring critical things such as firing pin stick out on a firearm when trying to diagnose a problem. Though my issue still has not been resolved I have been able to confidently measure and eliminate the firing pin as a variable. 

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