I got a new BM A3 M4 config. and to to range with 10 rd. factory mag only and PMC ammo.  Say, about every 5th round would have a failure to extract completely from the chamber and a new rd. would be picked up and cramed in underneath, of coarse causing a jam.
   Looking the bolt and dropping the mag cleared it.
   After cleaning, could not find anything broken.
   Took the gun to the range yesterday, same thing but not as frequent on some mags.  I took extra mags this time(Center Arms 30 rds.)
   Cleaned extra good this time, after 2nd shooting.
   First thought was bad mag or extractor, but both seem fine, now wounder if poss. need to clean the camber better and was sticking on a dirty chamber?

   Any suggestion as to cause?
   

I'm pretty certain it is the ammo in this case.

I had similar problems with my Bushy 20" with PMC ammo when I got my first one (now I use my own loads).

I switched to American Eagle and Remingtom and the problem went away.

Try different ammo and let us know!

Good luck!!

Yep sounds just like the problem I had with my Oly!  Mind you I was using Cheap Russian Steel ammo and the laquer messed up my chamber REAL BAD!  Used a chamber brush and lots of elbow grease and I was good to go.

Now the cheap Russian only goes in my cheap AK

I bought a Bushmaster rifle about two years ago and had the same experience. I had always shot PMC in my other two AR-15's and brought a couple hundred rounds with me to fire in the new Bushmaster.
I had lots of jams of all sorts and to say the least I wasn't happy.
I bought some American Eagle brand and it would shoot without a single jam.
The good news is that this only lasted about 100-150 rounds and suddenly the Bushmaster rifle would shoot the PMC stuff as reliably as the AE.
It seems the rifle only needed a little break-in and then everything was fine.

Hope it works out the same for you.

GunDude,
Princeton hit it on the head.
Take the Bushy to the range and suffer through 2-300 rounds,of which several will jam.
Clean everything but the bore,and use a good lube on all the moving parts.
The dadgum thing is tight,and all the parts are just getting to know each other.
It happens.I have seen it many,many times now.
We just got over 30 new Bushy M4's at work and for some reason they followed the wisdom of myself and another armourer,and found exactly what you are experiencing.
Once you get 2-300 rounds down range,this crap will fade,and your bore will be bright and almost carefree.
Good ammo is a requisite though.Keep the cheap stuff out for best results.
Mags with the Green followers help on the 3rd from last round angst after break in.
Green followers can be had cheap,and will breathe new life into old black follower mags.
Check CDNN's web site.
Don't fret.Ya got a good rifle.
It just needs some slapping around to understand what you want.
Cheers!
S-28

    Thanks to all for the info.  I don't need much of an excuse to go back to the range!

    I have a Bushy "Dissipator" also, and had two miss feeds in the first 30 rds and that was it, runs smooth as silk now.  Will get the M4 back to the range ASAP.