The hardness of the brass and how thick the flash hole web is in the base of the cases determines how much pressure the case can take. Meaning before you have brass flow or radial expansion in the base of the case.
Below Federal cases have the softest brass and the thinnest flash hole web. I have factory loaded Federal .223 cases with over sized primer pockets after the first firing.
CatShooter posted the information below in a posting when I was in a heated argument about how hard Lake City brass was and it was turned into a permanent article. The "heated discussion" was with someone who thought his Lupua brass was the best and hardest brass you can get. It got ugly when I told him I could buy 500 once fired 5.56 case at a small fraction for what he paid for 100 new Lapua cases.
How Hard is Your Brass? 5.56 and .223 Rem Base Hardness Tests
http://bulletin.accurateshooter.com/...ardness-tests/
TEST RESULTS
Using Rockwell hardness standards (.062″x100kg, Rockwell “B”), the brass measured as follows:
LC 2008 = 96
Lapua 223 Match = 86
Winchester 223 = 69
Remington “R-P” = 49
Summary of Test Results
Catshooter writes: “For all you guys that have believed that Winchester cases were tougher than Remington — you are vindicated, they are a lot tougher! However, Lake City and Lapua are ‘the pick of the litter'”. Catshooter notes that both Lake City and Lapua are significantly harder than either Winchester and Remington .223 brass. That’s something that we’ve observed empirically (Lapua and LC stand up better to stout loads), but now we have some hard numbers to back that up. Hats off to Catshooter for settling the hardness debate with his Ames Hardness Gauge.
Bottom line if you want tougher brass then switch to Winchester or other harder brands of brass.
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