The photo shows bolt over, being that the bolt either did not make is far enough back to get behind the rim of the round to strip it correctly out of the mag, or the mag is sitting too low or not recovering fast enough to get the round up to the top of the mag so the round can be stripped out of the mag correctly.


Step one, break out the CLP and a chamber brush and not only correctly clean the rifle before you fire it, but Lube the upper bearing ares correctly for break in with CLP as well.

With down, load only a single round into a mag, charge and fire the single round with the empty mag still in the rifle, and see of the bolt locks back on the bolt catch.

Once you have done step one and step two to confirmed that the bolt did in fact lock back, then we can trouble shoot the problem farther; knowing that at least the rifle is full stroking to begin with.

For starters, no company is going to send out a complete rifle bone dry.   Assembly and or storage lubes are used to keep the parts from rusting as the rifle sits on the shelve before being sold.  Further more, assembly areas are not clean rooms, so included with the assembly/storage lube, comes debris as well.


Simply put, no matter where an AR rifle or upper comes from, break out the CLP to remove such lubes, and a chamber brush to clean the the chamber of such lubes with CLP.

Next comes running a rifle bone dry, especially when brand new.   The anodizing and parkerizing are brand new, so in a rougher state than when the parts do make into each other.  Not only that, but you have gas rings that have not mated to the carrier gas chamber walls as well.   So as you can see, such areas will need to mate in to self polish out, and the CLP is not so much to allow the area to mate, but to allow the debris from the mating areas to be suspended and flush away as the rifle is fired.

Lastly, the OP has a bushmaster rifle, which the chamber may be a tad tighter than say a USGI rifle that will need some break in time, and even a carrier key leak..



So again, break out the CLP to clean the rifle fully, including using CLP with a chamber brush to clean the chamber by hand, and when you have just the B/C back together, put CLP around the base of the key, then while holding the bolt inwards, pressures the key with a air compressor (look for leaks around the base of the key to the carrier, and don't worry about the other small leaks like out the tail of the bolt which are normal).

And if you are using Hoppes to clean and lube the rifle, wrong solvents for the rig.  Hoppes cleaning solvent leaves behind a protective residue that cause nothing by binding/gumming problems, and the hoppes Oil has no cleaning properties in it, meaning that the fouling just build up fast to cause problem.


For the bore, something like Sweets solvent works fast to remove copper without a lot of scrubbing, then CLP with a chamber brush for the chamber and rest of the rifle.  If you start with the bore first, then as you clean the chamber, the CLP from it will do the protective short term storage in the chamber and  bore (even when you have run dry patches down the chamber and bore to leave them in a dry state.  On the rest of the rifle, think of the CLP cleaning as just changing the oil since CLP has a cleaning property to it, and will dissolve the fouling that you may have missed during oil changes.

Too add since I see the bullet button,   Some 10 round mags are Craptastic at Best!!!!!

Pull the mag down, CLP clean the mag inside and out, and put it back together.

Now load two rounds into the mag, shove the rim of the top of round down, then let it snap back up on its own.  Add another round, and do this test again.

If the  back rim of the top round did not come back up so the entire top of round is seated against the bottom of the feed lips, you will need to tweak the mag spring to get the mag to function correctly (to resolve bolt over/feeding problems).

With just the mag follower and spring in hand, trace the spring coil around from the bottom of the follower until you come to the coil wind on the back side of the follower base where it starts to come down. It at this 90* bend and where the spring leg starts to come down that you will need to bend the spring so the spring puts more pressure to the back of the follower when it in the mag.

With a quick tweak, and some retesting, you will have the spring tweaked correctly so as the rounds are being pushed down by the bottom of the carrier and snap back as as the carrier comes back, the spring/follower/round stack will correctly seat the top round against the bottom of the feed lips for a clean round strip without bolt over.

Again, pull the mags down and CLP clean them before you even bother testing them, and make sure that you have install the bullet button correctly so it is retaining the mags in the well correctly.

http://www.youtube.com/watch?v=nkwJ6yiyjm8
And note that the bullet button uses it own smaller spring inside the outer button body, and not the one that you would use for a standard mag release button.