Frugal Cartridge Length Measuring Device

There are many devices on the market for sale to assist one in measuring the maximum cartridge in one’s chamber.  They all are good tools.  Nevertheless, why not make your own?  The following is how I made a very inexpensive measuring device for maximum cartridge length.  This device lets me seat a bullet into a special case using the reloading press or actual rifle chamber for measuring the overall length.  Then the seated bullet maybe unseated, or pushed back out using a screw, after measuring and reused repeatedly.  This system works great and is very handy when setting up a new bullet in the seating die.  If you over seat a charged round during set up, then shoot it or pull it.  Using this device for initial set up prevents you from having to shoot some of those short rounds now and again.

Here is a 308 Winchester Case on 1/4 inch bolt with a 180 grain Sierra MatchKing standing by. The frugal unit comes in handy every now and then. Like measuring the overall length to land contact for different bullet weights or different bullet brands.

This procedure should work for any caliber or any cartridge.

Select one case to become the measuring device. One cartridge case is required for each caliber.  I do not believe that it matters if the has been fired in the chamber you are measuring.  Therefore, any odd case of the caliber should work and if full length resized it should fit into any chamber of that caliber.  If you have weighed your cases then select the one farthest from the average.  One with an off center looking flash hole is another good candidate.

This frugal cartridge length-measuring device is simply a modified cartridge case.  The case modified by drilling and tapping the primer pocket.  So, before drilling the primer pocket, knock out the primer if the case has one.  The primer may be remove by full length resizing, neck sizing, or just punch out the primer.

Drill out the pocket using the correct drill for the tap.  I have been using quarter inch bolts with 20 threads per inch for 30 caliber cases.  Therefore, I drill the primer pocket out using a number-seven drill bit.  For smaller caliber cases like 223 I drill and tap for a Number 12 screw thread.  After drilling and tapping, clean the case removing all drill and tap shavings.  I give the case a shot of 409 and rinse out with hot water.  After cleaning, the device is about ready. Next, you need a screw or bolt with a threaded length longer then the empty cartridge case.  After finding a long enough bolt, your frugal cartridge length-measuring device is ready for use.

Now just seat the bullet and measure the overall length.  Push the bullet out a little; seat it again, in your dies until you get the correct setting.  Use your gun to seat the bullet in the chamber and get your maximum overall cartridge length, to hard contact to the lands.  Set your dies for the correct bullet jump and check the settings with the frugal device.  Just one extra little trick, file, sand, and polish the end on the threaded bolt and it will not mar the base of the bullet.  When all is set load the bullet and use a fresh one from new bullet batch the next time.

I like using the RCBS Precision Micrometer to measure case and cartridge lengths.  It is easy to use and gives direct measurements with any bullet.  The Sinclair or the Stoney Point devices are also easy to use and may give better readings if your bolt has an ejector pin is place.  I have removed the ejectors from the bolts of my silhouette rifles so this little frugal device works great.  The case bottoms against the bolt face and not the case shoulder when seating a bullet in the chamber.  To get around this problem the frugal device maybe slightly modified.

For checking the maximum cartridge length using Remington 700 Type Bolts with ejector pins in place, just cut file or machine a slot in the cartridge base larger enough for the ejector pin.  Then the frugal device maybe placed on the bolt head without any pressure from the ejector pin.  The case extractor will hold the frugal device while you insert the bolt and chamber the frugal measuring device.  I have found this method yields the most consistence measurements.  When the rim of frugal device passes over the extractor in the bolt head, the bullet seating process may take place.  This may seat the bullet slightly deeper into the case.  Much like having the ejector pin in the bolt head.  If using Springfield Type Bolts where the cartridge must be placed in the magazine first.  This type of bolt head forces the cartridge rim behind the extractor while chambering.  This type of bolt heads may work just fine with the frugal device while the ejector pin in place.  I have not tried that and I have a Springfield.  The difference it the resulting measurements varying has much as the difference case size to the chamber size.  Therefore the best way to used the frugal device is removed the ejector pin or cut a slot in the base of the case used for the frugal measuring device.  Nevertheless, always place the frugal case on the bolt with the rim behind the extractor.  On the other hand, you could buy a measuring device form Sinclair.  Just because it works for me does not mean it will work for you.

Larry Medler

Rifle Silhouette Shooting

Silhouette Ballistics

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July 8, 2003