One of each. The shorty is a Black Creek Precision dedicated lower and the other is a Hahn Precision mag block adapter in a Bushmaster lower.
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When I first built the BCP gun, I had a ton of stove pipes. Then I tweaked the ejector and it's been 100% since. The Hahn was different only because I adjusted the ejector right off. I also only use Metalform magazine. I haven't tried other brands, yet.
Not sure what issues you're having, but those are a couple of things to take into consideration. Also, I'm running DPMS-style triggers, one's an ALG ACT, the other is a DD milspec trigger.
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Nice brace ya got there ^^
https://i.imgur.com/tgmvsKn.jpg?1