Snap caps are "dummy" cartridges that allow a shooter to dry fire a weapon without damaging the firing pin. A number of current production guns are said to be safe to dry fire, I guess I'm kind of old school and try to have snap caps for all of my guns. They are handy if for no other reason than they allow one to release the tension on the firing mechanism while the gun is in storage. Commercial snap caps are available for most of the common cartridges out there. If you have a .30-06 or a .270 or a .45 Auto or a .223/5.56 NATO you'll not have any trouble getting snap caps for your guns. On the other hand if like me you shoot a number of wildcat cartridges and old military or old single shot cartridges your likely to have a difficult time finding anything and if you do it's likely custom made and expensive. So if it's going to be custom made why not be the custom maker in your own workshop. This method came about while I was doing some other custom work to create cases for an OAL gauge. So if you've come this far come along and see how I've made snap caps for an odd ball cartridge or two.
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Step 1: A Little of What You'll Need
First you'll need an example of your chosen case - either new or fired. NO LIVE CARTRIDGES PLEASE!!!!!
A 1/4x20 tap and a #7 drill
A supply of 1/4x20 nylon bolts I get these at whichever big box hardware store I'm close to when I need them. I initially bought 2 packages of 2" bolts I've made 8 or 10 of these so far and I'm on my second bolt for this Inscrutable.
For tools, you'll need someway to hold the cases without distorting them while you drill out the primer pocket and thread it. You'll also need a tap wrench and your reloading equipment as you'll want to full length resize the case and seat a bullet in it to complete the cap.
You will also want some type of lubricant for the tap. I've used Tap Magic and Brownel's Do-Drill and really don't have a preference. I've been told that Tap Magic can cause rust, but since I make every effort to clean up any lubricant I use it hasn't been a problem.
Step 2: Drilling the Hole
I'm fortunate in that I have a Sherline lathe in my shop and that is what I use to do the drilling. The first picture shows the center drill set up to start the process and the second shows the #7 bit completing the hole
Step 3: Tap the New Hole
After completing the hole I use the tail stock mounted chuck to make sure the tap starts straight. I then remove the case and tap and complete the job of tapping by hand. I find that case brass tends to the hard side and recommend a good lubricant to do the tapping. I have found that it often helps to drill the hole a little larger than the standard tap drill size. With the 1/4x20 I've gone as large as 7/32 and still have enough thread to hold the bolt.
Step 4: Insert and Cut Off the Nylon Bolt
After the hole is threaded I turn the nylon bolt in about 5 turns and return the assembly to the lathe where I use a parting tool to cut the bolt off flush with the case head.
Step 5: Add a Bullet and Your Done
The picture shows the completed case still in the lathe chuck. The lead photo shows the completed 7.62x54R snap cap. I have found that the 1/4x20 size bolt works okay for cases with large primer pockets but I've been less than satisfied by the results with this size in small primer pockets and continue to experiment with those to determine a suitable size. More on that latter.