AR15 Bolt Lockuped



Newbie question:

I bought my first AR15, this used Bushmaster Varminter earlier this year and had been shooting same ammo, Wolf Polyformance .223, more than 600 rounds with zero issue. Two weeks ago I cleaned most parts, including BCG for the first time (I know I am lazy). I don't know what lube the previous owner used but I used froglube. Then I bought a new Hexmag. When I got home, I compared it with the original mag came with the rifle and also a Pmag (10/30) and found the follower in hexmag is slightly different. So I tried it with dummy round. Then the bolt was locked up. I had to slam the stock when pulling charging handle to eject the dummy round. I thought maybe it is the round though the ones I used are not plastic, instead, they were made of real ammo. Anyway, I decided to give it a try with real ammo today. With 10 rounds in the hexmag, after the first round chambered, the BCG was locked up again. After pulling charging handle really hard for several times, the round was ejected. Then I tried the old mags which both worked fine when full loaded. So I thought it must be the hexmag. Then I tried loading 2, 4, 6, and 8 rounds with hexmag, it worked. The range master told me that possible reason was that I either need to clean it better or had not lubricated it enough if it is not the mag. Thus I took it apart and found it was kinda dry. So I put some frog lube on all the surfaces of the BCG and chamber. Then I tried 10 rounds with hexmag, damn it, it was locked again. At that point, I was 100% sure it was the hexmag (either the spring is too stiff or the different follower). But when I went back to my old mags, this time, the BCG was locked up too. One thing I noticed was that neither Pmag or Hexmag could be inserted when the bolt was closed after relubrication. I had to keep the action open and insert the mag. As the mag was inserted, the bolt closed by itself and then locked.

Now this issue is really a puzzle to me. I will appreciate any advice or suggestion for a troubleshooting and more important, whether all the stupid procedures I have done to my rifle could have caused any damage or safety concern. Please forgive me if I used any wrong termonology ---- again, I am a newbie.