Measure Your Chamber Length with Home-Made Modified Case

We are sad to report that long-time Forum member Frank S. (aka fdShuster) passed away last year. Frank was a very knowledgeable shooter who was always willing to help others. Here is one of Frank’s smart inventions. He devised a way to measure the length of a rifle’s chamber using a fired cartridge case. This lets you find your MAX trim-to-length for any chamber. Frank’s system works by cutting a “collar” from part of the case neck. This then slips over a bullet seated in a case loaded without powder or primer. As you chamber the dummy round, the collar will move back to indicate the full length of the chamber. (Make sure the bullet is seated well off the lands so the dummy round can chamber fully.)

The pictured gauge can be home made (for free) with components you already have on hand. Frank explained: “I used a Dremel cut-off wheel to cut the front half of the case neck off. A jewelers needle file to de-burr both rough-cut edges. The cut-off surface does not need to be perfectly square, because you are using the original straight mouth to make contact at the front of the chamber. Seat any old bullet to the approximate normal seating length. Next apply a tiny drop of oil on the ogive of the bullet, and slide the ‘collar’ over the bullet. Then chamber the dummy round and close the bolt. Extract the round slowly and carefully and take the measurement with calipers (see top photo).”

Frank’s DIY chamber length gauge works well. In a related Forum thread, Frank posted: “I’ve compared length dimensions doing it this way and with the chamber length shown on my chambering reamer drawings, and the Sinclair gauge, and they are all within .001″ or so.”

Commercial Chamber Length Gauges May Not Work with Custom Chambers

Frank did use Sinclair chamber-length gauges for some applications. These bullet-shaped gauges slip into a cartridge, but “it’s inconvenient to order that little gauge only… without spending $6 shipping for a $7 item.” Moreover, the Sinclair gauges may not fit a custom chamber with a tighter neck dimension because the diameter of the ring at the end is too large.

As an alternative to commercial gauges, the collar-type, homemade gauge will function properly in a custom chamber. The homemade gauge will work with smaller-than-standard chamber neck dimensions, as long as you use a piece of appropriately-turned fired brass that fits your chamber.