We don't know where he got the "kit" he bought, and we don't know whether hw assembled it properly either, so anything is possible here.
Suffice it to say that the man has an improperly functioning rifle. To me, this is the down side of the "build it yourself" movement. Too many people are building up ARs (and AKs too)without really understanding what they're doing, how to check for proper function before they get to the range, and what to look for in the parts they buy.
On the other side, too many distributors are buying parts and assemblies from subcontractors who do no inspection and guaging of what they're shipping, and it becomes the purchaser's job to be the parts inspector.
It's not just the marginal outfits either. In the past couple of years I've gotten out of spec, and even broken parts from Rock River, DPMS, and Bushmaster. It's gotten to the point where I'd rather buy used GI surplus parts at the gun show, than new commercial stuff.
All the big outfits are doing a fine job with uppers, lowers, and barrels these days. Just wish the small stuff was always of equal quality.