I sometimes get customers who send me text messages with questions about the different services my little shop offers and other gunsmithing questions... So this guy sends me this text, (don't know him from Adam) includes this picture of this G21 (I think a Gen 4). His question to me was... "Can you explain to me how this could happen?" I texted him back and exclaimed to him "Holy ****!" and asked him what happened? He tells me... "This was the second one of these I've done and the first one shoots just fine. That one was mine! The one in that picture was my buddy's G21. What do you think happened?" I told him that from what I could see it looked as though there was an overpressure failure just aft of the muzzle. I said that the barrel looked to be an aftermarket compensated barrel, is the slide port matched? He then tells me... "Oh yeah! I matched 'em right up! I used the exact same measurements as the Lone Wolf barrel I borrowed from a guy." I asked him... "You did this yourself?" he told me... "Oh Yeah!" I then asked him how? He said... "I used a mill and just drilled right thru the slide. The hard part was cuttin thru the barrel. I had to used a Diamond grinder wheel! Man them barrels is hard!" He then tells me how the pistol is on it's way to Glock for warranty... I had to laugh!