First off, pull all the way back on the charging handle, and look where the bolt face stops against the back edge of the ejection port window.  The bolt face should stop 1/8" to 1/4" in front of the back of window edge.  Also, when you are pulling back on the charging handle, the last inch of pull should not increase in tension that the middle to back of pull.  If it does, then either the spring is coil binding out, or you have FCG wedging going on instead (disco spring not installed large coil side down into the trigger tail, or the hammer tail too long)

To weed out problems with the charging handle itself, with the CH pulled all the way back, push back on the bolt face itself and see if the bolt will go back any farther. If it does, then you the CH is defective.

Next,  need to check the depth of the receiver extension void.  
The Carbine spring should be around 10.5" long, and the depth of the carbine receiver extension should be 7" from the lip of the tube, to the back of the inner void.  If your butt stock system uses a butt stock bolt, then make sure that the butt stock bolt is not too long, and now protruding into the back of tube void to limit the buffer (instead of the buffer bumper being able to contact the inner void back wall cleaning instead).

Now shotgun the upper open and insert a empty mag.  The catch tab should cleaning catch the back of the follower, and raise the catch all the way up.
If the you have a know good mag with  a strong follower spring and the catch is not binding in the lower receiver (just spring tension pulling it back down), then chances are when you install the bolt catch, you did not clean out the bottom of the spring channel and crap in the bottom of the channel has the spring over compressed.


As for the ST-1 buffer, bring me up to speed why you went with the heaver buffer.  The standard weight buffer should work fine, and the heaver buffer is reserved for ammo heaver than 62gr (slower burning power, which will increase port pressure, causing the bolt to unlock too soon, and the heaver buffer is used to slow the unlock back down to normal).  Hence during live cycle, if the rig should be using a standard weight carbine buffer, and you slap a H series buffer in it, you chance the bolt unlock too late now, and the rifle short stroking instead.

What you got was a receiver extension tube for the bb airsoft rifles, and why the depth of the void is not deep enough for an actual AR-15 rifle instead