300 AAC / Blackout Brass Trimming jig for Cutoff Saw

thingiverse

This jig, designed for a Harbor Freight #42307 Mini Cut-Off saw, facilitates trimming .223 / 5.56x45 cases to make 300 AAC cases. Positioning the case based on its shoulder instead of the neck helps eliminate variations caused by different neck lengths. The jig features a 0.050" wall around its pocket for better case holding and positioning. To use it, remove the saw vise and place a 0.050 shim under the jig. Some adjustment may be necessary to ensure trimming just behind the shoulder. Secure the jig using 1/8" x 2" toggle bolts. This is an ongoing project; improvements for easier neck removal are under consideration, and both STL and Solidworks files are available for modification.