So I insert the mag, pull back the charging handle and release. The bolt closes & locks, then I drop the mag, eject the round and the primer has been dimpled. This is a bushmaster upper with around 700-800 rounds through it. I'm not familiar with the AR Bolt. Is there a firing pin spring that could be worn out?

It is normal don't worry about.

That being said, don't reload the same round over and over and over and over.

eta - and over.

eta - It is because the firing pin floats around in there a little bit, and the forward momentum is enough to dimple the primer.  But not enough to set it off (provided you are shooting good ammo with good primers).

But you should still never chamber a round unless the rifle is pointed in a safe direction.

Thanks, First AR, First time I've charged it. I know this is bad with 1911's but didn't know about AR's.

I Searched and checked the FAQ but couldn't find anything.

Quoted: that's what I meant renegade360, it's a common question and it's NOT in the FAQ. Kind of obviates the need for a FAQ.

Does any of the FAQ actually work?  

I learned that on a thread on this site many months ago. and yup, mine does the same thing. I still shock non AR people when i show them this, ( this includes new LEO's too). I had a short conversation on this board about the same time  that he had an AD while on a call. chambering a round on his patrol rife. he was saying luckly his SGT was standing beside him when it happened and saw what he did, (everything right) including pointing the muzzle to the ground when letting go of the charging handle. blew a chunk of asphalt to heck, no injuries.
he advised me to ride the CH down and use the Foward assist to seat the round if i ever needed to chamber one in the field.  I learned from HIS lesson.. whoever it was , THANK YOU.  and i tell everyone i know that handles AR's about this "AR-ism".

My dad's MAK-90 does the same thing.  I just rearrange the load in the mag if it's done repeatedly to the same cartridge.

he advised me to ride the CH down and use the Foward assist to seat the round if i ever needed to chamber one in the field.

 Which is a great way to induce a malfunction.  

Quoted: he advised me to ride the CH down and use the Foward assist to seat the round if i ever needed to chamber one in the field.    Which is a great way to induce a malfunction.

+1, don't do this.  Just chamber the round in a safe direction.  Never ride your CH down.  Drop your CH as hard and as fast as you can.  You will never even come close to being able to do it as fast as it falls when you are shooting it.  

If you do have a slam fire it is either something wrong with your rifle or you are using bad ammo.

Bad advise to ride the CH down.

eta -  No offense Bloodhound_K-9, but what you are doing is dangerous and should not be given as advise to anyone.

Most military style rifles like the AR, AK, and SKS use a free floating firing pin (no spring) So some say not to use ammo with soft primers (some commercial, or reloaded ammo) because the posibility of a dicharge or slam fire  when charging the weapon.

Tweak, most of the FAQ links are dead.

Quoted: Tweak, most of the FAQ links are dead.

He knows.