not to dump on CDNN, but they sell ohio rapid fire built guns. they are known to cut corners on the cosmetics and use a lesser quality sear and trigger setup. john mcguire uses the best sear and trigger, by karma metal products. i use that as well. as said above if you build yours as i did, you will be intimately familiar with its inner workings and will always be very proud of your own build. i farmed out the machining and parking, since i dont have the equipment. www.1919a4.com has answers to all your questions. there was a post today by a guy selling the kit, the karma trigger and sear, and doing all the machning for you for only $475. hard to beat that. then you just need rivets and a plate and park it.
as for some of the builds not cycling 100%, there are a lot of variables to eliminate, but you can get them to run. i am pretty sure you will run into that with a orf build anyhow. if anybody wants, im or email me. i would be happy to offer my advise. a word of caution- if you thought black rifle disease was bad, wait till browning mg disease sets in