My buddy at work has a colt sporter.  Its preban, but with no bayo lug.
He says he fired a few rounds, then it quit.  Jammed, locked up, the bolt won't move, and he cannot separate the upper and lower recievers.  I let him borrow my AR tools for a week.  Today he brought those and the rifle to me.  He couldn't get it apart still.  

I took the rear take down pin out, and the rifle won't pivot.  The bolt is stuck mid travel.  No help from forward assist or charging handle.  I unscrew the front take down pin and remove it.  The two halves are loose, but will not separate.  I manually reset the trigger, and examine things.  Colt has put some extra junk in the reciever, I guess to prevent modification.  I cannot get the two halves apart.  So I take the stock off.  I can see the buffer retainer, and can reach it to depress it.  The buffer tube won't budge.  Period.  So I start taking off the hand guards.  The first front sight base pin popped right out.  The second..... well lets just say I have ordered a new front sight base and pins.  The flash hider came right off, and so I tried to remove the barrel nut.  The Yankee Hill wrench broke, and then I broke it again.  Two out of three pins gone.....  During this process, by some miracle, the upper and lower halves separate.  Now I can see that the detent for the buffer does not hold the buffer tube.  I don't know how its fixed in place!  I took a cleaning rod, and after checking the bore, let the rod drop under its own weight a few times.  To my surprise, the bolt fell right out!  Then a shell casing fell out of the chamber.  The round is marked as such "NPA" on top and "5.56x45" on the bottom.  I have no idea what brand it is.  Its a brass casing.  The primer is very loose, like the powder charge blew out of the back of the case.  There is no evidence of a bullet being stuck in the bore, its completely clear.  Being a noob, I suspect a too tight bullet, or a faulty casing causing the charge to blow out the back.  I cannot tell what caused it to lodge in the chamber, as the case is undamaged save for where the extractor ripped over the rim, and where the spring loaded pin beat the bottom of the case.  He used the forward assist and you can see where it beat the round.  I guess its possible that a thin wall casing expanded just enough to sieze.
Again, all speculation.  So far its just a faulty round that caused this colt to fail.  No broken parts other than a ruined FSB pin and a really marked up sight base.  I spent an hour on one pin!

He runs this gun very dry.  I see no lubricant anywhere.  I will clean it and lube it for him, and I have ordered a new FSB from del ton to replace the one I messed up.  Hopefully he will be back in action by the end of the week.  

All in all its been a fun yet frustrating experience.  I learned a few things about colts.  I got to help out a friend.  I am still mystified as to why the bolt was locked in place if the extractor was able to damage the case rim.  Perhaps it didn't pull all the way over?  Why if the charging handle was unable to snatch the round out with great force, did the light drop of a cleaning rod do it?  

that happened to one of my teammates during a 600 yard match one time.  his was b/c of lack of lube too.  we just took a strap wrench to the buffer tube and removed that, then oiled it up and reassembled.

I harassed him today about the crappy ammo and brought him the cartridge casing.  He says he bought 800 rounds for $90.00.  He doesn't know what brand it was, just that he bought it from some old man at the gun show.  I run georgia arms canned heat without issue in my bushy. at least its military brass.  
One of my coworkers thinks the round may have been overcharged.