When I bought my first short-chambered Auto-5, I ordered a Short-Kit for my MEC 600 Jr. I stuck to my old 2 3/4” recipe, just reducing the shot enough to fit. These shells fed and fired fine. Later I ran across a thread on 16gauge.com that talked about the Hartin Crimp. Since then I’ve put away my Short-Kit and just use the full 2 3/4” load in the shorter case, adding an overshot card and crimping it in place. The loaded length of the shorter shell is the same as the longer one. These shells feed and function great as it’s the fired length that matters. In the picture, that’s a factory 2 3/4” shell next to a Hartin crimped 2 9/16” hand load. http://www.16ga.com/forum/viewtopic.php?t=18347&postdays=0&postorder=asc&start=15
If you’re going to load 65mm shells, you’ll need to shorten your hulls. Ballistic Products sells a tool that works, but it’s tedious to use. https://www.ballisticproducts.com/Trim-Doctor-II-Shotshell-Case-Tool/productinfo/TRIM2/ Then I found this tool sold by Byrdog on 16ga.com: It works as well as shown in the video, and I went from just loading a couple boxes at a time to loading only short shells. At least until I run out of factory 70mm ammo.
I should mention that I’ve had the best results with the Hartin Crimp using paper hulls. I usually seal the plastic hulls with a drop of hot glue.
