In the past few months I've had customers bring in "part kit" AR-15s that do not function correctly. So far there have been two main problems, the dust cover not closing or warping, and defective hammers. The dust covers have been made of flimsy metal or the detent not positioned correctly, although one had a bent pin which didn't allow the cover to freely open. The problem with the hammer is that the portion which catches to the sear chips off enough that it won't engage the sear properly. This doesn't lead to full auto as the parts are semi auto in design. It does however let the hammer follow the carrier and not engage the sear to re-cock. The only course is to replace the hammer with a quality one. Customers are getting upset due to the fact they are spending way more money than they thought "building their own" rifle, expecially when I point out other issues like carrier keys not staked down or barrels that are not even marked. When you add a bench fee, parts cost, and test fire ammo costs, there is practically no savings. If a company made quality parts and barrels, they would put their name on it.