I have an 870 supermag in 12 ga. and it keeps destroing the choke tube it will eat up the choke to the threads and maybe some of the threads.  its done this to several of them and i was wondering if anyone could tell me what is possibly wrong.

yeah... what are your combo between load and choke?

I shoot good old value pack shells with the mod. and full then i shoot 3.5" steel with the full to.  the chokes are remington factory chokes.  could the problem be that i don't get them in tight enoffe?

I never heard of it either. Do the choke tubes stay tight or are they constantly working themselves loose? You must ensure they are screwed in all the way and tight. Did the chokes come with the shotgun or are they aftermarkets?

Quoted: .. and it keeps destroing the choke tube it will eat up the choke to the threads and maybe some of the threads.

This part has me stumped. A properly installed choke has no exposed threads so I don't see how shooting can damage something thats not exposed? If they are working loose then that might help explain things.

I think we need more information from the original poster.

Are the chokes flush or extended? The flush type are easy to see if they are working loose. You could have loose extendeds and not realize it unless you check.

Just quessing really until we get more info.

The chokes are standard flush mount chokes they are the exact same thing that came with the gun.  the problem is that i will be shooting and go to change the choke and pull the one out of the barrel and the area below the threads will be missing and some of the threaded part of the choke.

I have Remington shotguns and never had this problem so I can't help but I'd advise you get your gun to a gunsmith and have it inspected. Any gun thats shooting out portions of its chokes has a serious problem.

Time to wander into the deep end,

What comes to mind is that you are not using a lube on the choke/barrel threads.  The threads will seize/gall and cause the threads to wear out rapidly.

Another thing that comes to mid is that you installed one of the tubes too tight, you may have chipped the barrel end of flair (just before the threads in the barrel).  This causes the wad to grab the choke and try to push it out with the wad. To see this, insert a choke hand tight, and shine a flashlight down the choke.  There should be a slight step from the barrel, down into the beginning of the choke.  If the choke is sitting above this flaring lip, then you will need to either replace the barrel, or rework the beginning of the chokes to allow the wad to pass by without binding.

Also, when you clean the barrel, leave the choke in the barrel.  Without the choke, you get plastic fouling in/at the end of threads, and can build up to the point that there is a void between the choke and the barrel flared lip (causes the wad to bind on the way out, and tries to spin the choke/mars the threads. If you have been cleaning without the chokes in and the flaring lip is all right, then it's time to get a dental pick and clean the locking/flaring grove.  This will allow the choke to seat correctly, and prevent gapping/canting of the tube.
Note: a toothbrush works great to clean the plastic/crap out of the threads.

As for choke lube, nothing really fancy needed, just some type of light grease to prevent galling of the threads when tightened down.

To add, if your reloading steel shot and running a full choke, make sure that there is a little of the wad cup pedestals above the shot.  Overloading a wad with steel is bad. The steel shot gets forced out of the cup and scrapes down the side of the choke tube during the constriction.  On some shotguns, steel is not recommended in the full choke due to just this.