Friends, put together a budget largeAR style rifle.  
Faxon 20" barrel.  .308 7.62x51
Areo upper and lower.  
Large recoil spring and shorty buffer like it should have with a cheapy ar15 buffer and stock.
Ar 15 mag catch.  

Problem I am having, mag sits too low and bolt misses case head.  Mags drop out.
I already know that I need to change to a longer or heavier spring.  
Steel mags drop out at firing and magpull all but drop out.  5 rounds in the mag only.  

Is there a specific mag release and button on the market that will help me out?
Maybe just a regular ar 15 release that isn't a budget parts kit part?  

I have spring stock so I can have about any spring I want.
Curious if anyone has had this issue.

Use the AERO LPK or at least their mag catch. There were some issues reported IIRC with bolt catches and mag catches. I went with their LPK and so far all is good.

Thanks John.  
That cast cheepy mag release I have in it is probably to blame some I bet.  
Not sure.

Well I checked my AERO and found I did use a taller mag catch button. Replaced the AERO mag catch with a NORGON.
And guess what - Lancers don't catch - they fall out. Magpul will catch and hold but if I depress the follower using the bolt catch - and flick the mag - it falls out.
Now same with the normal mag catch.
Wonder what is going on now.

I used a heavy spring and ground a bit on the release itself.  
I put in an extended button too.
So I think I got it.

mailed Areo and they said I would have to use their catch.
Which I could purchase on their sight.
So I endeavoured to screw them out of the sale and did the above.  

I only have the magpul and the psa metal mags to try however.

I had to return a M5 lower to Aero because the mag catch recess was not milled deep enough to allow the mag catch to protrude adequately into the mag well. I was told there were a bad batch of lowers that had this problem.

Could this be your problem?

I just built a ar10 with aero m5e1 builders kit and a 20" faxon fluted barrel and a toolcraft NiB BCG. I am using a a2 tube with a tifle buffer and a JP .308 spring. I use pmags exclusively and used strike industries mag catch. I have 0 issues. Just put 60 rounds through it this morning!

Most likely this, or perhaps you're not tightening it enough? With the Aero lpk, they did not make a longer catch, but rather a taller button. If it's the AR15 size button, you basically have to have a couple threads protruding through the mag button itself for it to apply adequate tension on the spring/magazine.

I made sure the catch is tight against the lower. Calling Aero.

Sounds like the location for the magazine catch hole is too low, especially if it does this with all the magazines you have tried, unless you screwed something up with the recoil system to the point that the BCG won't retract far enough to the rear.

What do you mean by a "large recoil spring and shorty buffer like it should have"?

 
A large pattern spring "heavier" and a dpms style short buffer for using a regular ar15 carbine tube.  
The tube is a longer version though by a 1/2" and angled slightly.    
The type of modifying I did to the catch itself let the catch go deeper in the receiver.  It was cast and I ground down a bit of flashing and whatnot.  
It was the button they said needed to be their extended version for the large lower.
I had an extended regular ar15 button and I used a heavier spring.  

I probably didn't mean the whole screw em thing.  Just didn't see an option for ordering just those pieces and was ornery at the time.
Shift work.  

It could well be a bad lower.  I didn't think of that.    

The type of problem I was having was a bolt over.  Bolt catching the cartridge mid case and bending it as it was trying to chamber.      
It was doing it with fed 175 gr match as well.

They are sending me a new mag catch to see if that helps mine. You need to use their recoil system to ensure proper operation many have said.

Sent back to Aero for a look see.
Replaced