i can get the bolt the unlock if i bump my rifle by the stock. Is this normal?

try a different magazine

Yes it is normal. Don't rely on it to charge your rifle though, Use your charging handle please.

<Edited.............comment removed.........dpmmn>  

Yes.  Think about it.  The bolt catch is spring loaded as is the BCG.

If you bump the butt downward, it will retract into the buffer tube and unload the tension on the bolt catch allowing it to drop.  When the BCG returns forward, there is nothing to stop it from going all the way home.

Yes but when you pull the charging handle back it puts extra spring pressure onto the bolt so if you have a dirty gun it has a better chance of going into battery.

100% agree.  Just trying to explain why the BCG releases when the butt is grounded.

Inertia.

Ok, I thought you were advocating doing that.

Guys I don't mean the bolt catch releasing the BCG that was locked back. I mean my bolt would unlock, meaning it rotating and getting pulled out of the barrel extension/chamber, just by inertia. Is that normal?

So the bolt was going forward while the BCG stayed behind? Like you had to take the gun apart and reattach the bolt to the BCG???

Well, depends on how hard you are smacking it.

The short answer is yes because that is the way the carrier works.  Reward movement unlocks the bolt.

It SHOULD take a lot of force to do that as the carrier should still be in contact with the buffer which is pretty heavily spring loaded.

Can you manually move the carrier to the rear easily by punching it with your finger through the ejection port?  That should not happen.

No. I mean with the BCG forward, when I bump my rifle by the stock, the BCG would move back, unlocking the bolt.

How much have this rifle been shot?

I can do it with the hammer cocked, but not when the hammer is down... is that normal?

how old are the gas rings on the bolt?

NOT normal with the hammer cocked.  You should have a pretty strong pressure on it from the buffer.

Need more info now:

Carbine, pistol or rifle set up?

Take the upper off the lower.  The buffer should be riding on the retaining pin. Push it with your finger. It should not move easily!  Yes/no?

Is the rear of the carrier flush with the end of the upper?  It should be and not be recessed into the upper.

It's a carbine set up. The carrier is flush with the receiver. Pretty sure the its butting up against the buffer no problem; it's not rattling or anything. How easy is "easy"? I can press the buffer in, with maybe like 7-8 pounds of force?

I mean when I pump the rifle lightly, like when I set it down on the ground, I can see it move maybe 0.2 inches... it makes me wonder if I'd cycle/charge the rifle if I smacked it hard enough you know?

I'm going to have to defer to someone else on this.  I don't have a 9mm set up.

For a standard carbine, that force sounds about right.

ETA: let's cut to the chase.  Have you shot it and does it function?  If so, go with it and quit smacking it on the butt!  

Yeah that's cool. I shoots fine. I just get curious sometimes haha.

Normal.  Inertia is going to cause the carrier to move rearward when you slam the butt into a hard object.  Any auto will do it as long as you hit it hard enough to overcome the recoil spring and friction.

This. You can do it with pistols too if you do it hard enough.

This was a problem with many earlier submachine guns.  If you bumped the butt hard enough the bolt would come back far enough to strip a round out of the magazine.
When the bolt closed, being a "slam-fire" blow back weapon, it would fire.

Shortly thereafter, SMG designers began using some method of locking the bolt so it couldn't do this.
As example, one of the early guns to use a bolt lock was the German MP-40 SMG which had a bolt handle that could be pushed in when the bolt was closed, locking it shut so it couldn't move back.
The US M3 Grease gun had a safety hatch.  With the hatch closed the bolt couldn't move back.

Among the designs that would fire if bumped was the British STEN gun.  
I once read a book by a Brit Commando who described Commando training in North Africa.
They'd be driven down a road and would bail out of the bed of the truck to simulate a parachute landing.
They found out the hard why about the inertia firing problem.  The author said that as a soldier would hit the ground the way they carried the STEN gun would cause the butt to hit the road hard enough to fire it.
The carry method caused the muzzle to be pointing toward the truck.
He said that would almost always cause the next man coming off the truck to be shot.
They quickly changed the carry method.

Most all semi and full auto rifles will allow the bolt to move to the rear if struck, but since they aren't slam fire, they normally won't fire, but may chamber a round.

Not only that, I find it hilarious that the OP made the error of replacing the intended word "to" with the word "the." It's not like we didn't know he meant "I can get the bolt TO unlock..." But then grammar Nazi here chastises him for his grammar by forgetting the apostrophe in the word "can't." And since "cant" is a word often found in firearms discussions (since the cant of a holster or weapon is often discussed), he committed just as bad a grammar error as OP. I would call it ironic if it weren't simply hypocritical.

First off Op don't pay attention to some of the less than desirable responses.  My thing is if you have a question then ask it, that's the beauty of arfcom.  From my experience with AR rifles even when the hammer in the cocked or even when it isn't it is perfectly normal for the BCG to move reward (more so when the hammer is cocked) when the butt stock is struck on the ground however, it is usually not enough to cause an issue unless it is violently struck/mortared. You will also notice if the BCG is locked to the rear and you slam the butt stock to the deck, it will release forward. Nothing wrong with that bro, it is what it is.  I hope this helps and welcome aboard bro.

Yep.  It's the main reason the forward assist exists.  Doing a 3-5 second rush "Army style" involves using the buttstock of the rifle against the ground as you drop to the prone position.  Often as not, this causes the bolt to unlock, and without having any protrusion from the bolt, there is nothing save cycling the charging handle again to get It back into battery.. unless you have a Forward Assist.  

I agree...I get tired of people on here correcting other’s grammar (who cares!!!!).  
Lets spend time talking about firearms not “spelling”.

1.  If you are doing 3-5 second rushes, you are doing it live fire.. the bolt is hot.  Even if you have a glove on.. plus you are introducing dirt.  Use the forward assist.  

2.  Getting a finger to make the bolt go forward in that situation requires fine motor controll.  Slapping a forward assist requires gross motor control.  Under stress, you have less fine motor control, so having a big button on the back of the rifle is a good thing.  

If you don't like it, buy one without it.  Just understand that in the real world of Soldiering, it has a real use.  End rant.  Back on topic...  

I think he's just frustrated at the fact that so many out there seem to think that the FA is completely useless, with some even going as far as saying the feature should be axed.