Definitely invest in some good mags. They are becoming cheap again and I've picked up Pmags and Lancers for under $20 last weekend.
Here's another suggestion during break-in of your AR. With good ammo and mags, put one round in the mag and fire that making sure that it locks the bolt back every time. This will ensure you have a good cycling and the bolt catch and mags are working good. If its not locking the bolt back, then you know its possibly undergassed, or your mag is not reliable, or the bolt catch might not be engaging.
After you verify that, you can shoot 2-3rds or so per mag to make sure its stripping the next round properly. If it does that fine, then you can load the mags to capacity.
Once you are 100% sure that your mags and ammo are good, then you can see if your gas block is mis-aligned, or something else is out of spec with the rifle. One of the issues I came across during my break in was improperly installed trigger spring that caused a FTF.
Also once you are done shooting, take the rifle and re-tighten any screws or parts (castle nut, screws on your rails, etc) and inspect that all parts are tight and in place. Check your takedown pins, safety lever, buffer, buffer retaining pin and everything else. Sometimes a part will come loose that you don't notice and causes some type of failure.
These are just some of the things I've learned from troubleshooting my own builds. Hope that helps and happy shooting!