May 15 09 1:36 PM
|The Hornady LNL OAL gauge works very well with a little practice. A "modified case" is required for each caliber.
The heads of these modified cases are drilled and accurately threaded with a small-pitch tap. This size of this tap is unusual: 5/16 x 36. the 36 refers to threads per inch.. Use a 9/32 drill bit to drill through the case head before using the tap.
This all must be done accurately.
copy from internet
If the hole is not concentric or not parallel to the axis of the case, or if there is slop in the threads, this will affect the accuracy of your OAL measurements.
You probably won't be able to find the tap locally; it is available from MSC Industrial Supply. Part number is 04841367.