March 20, 20202 Update: This week I worked on filming a video about how the standard-pattern muzzleloader is made, and did some more experimenting with 350 Legend.  Magazines have proved somewhat problematic: the Legend cartridge will not stack correctly in a standard 5.56 magazine, and as far as I can tell, nobody makes a standard-capacity magazine for the Legend--they are all low-capacity ones, mostly 5- and 10-round.  The closest I could find to a regular magazine was a 20-rounder, so I ordered a pair of them to try out.  In the mean time, I also tried modifying a polymer 5.56 magazine, first by grinding off the ribs toward the front of the magazine, and then by adding shims at the back.  By this method, I was able to get 350 legend cartridges to stack almost correctly, but the magazine still wouldn't feed them reliably.  In the course of forming 350 Legend cases from spent .223 brass, I found that while some .223 cases can be neck-expanded as-is, many will split if the mouth of the case is not annealed first.  However, if the shoulder of the case is annealed, it will crumple during the neck expansion process, resulting in an un-usable case.  Thus, I developed a method of consistently annealing the case mouth without annealing the shoulder: first I fill a plastic cartridge tray with water, and then with empty cases, so a batch of cases is held upright, with about the bottom third of the cartridge submerged in water.  Then I run the flame of an oxyacetylene torch over the cases until just the mouth of each case starts to glow red.  So far, my case-forming success rate on cases thus treated has been 100%, compared to about 50% for un-treated cases, and 0% for fully annealed cases.  Anyway, this weekend I plan to upload another armor-testing video.