i was wondering if i have to get a better barrel for any ar 15 to shoot the constant 100 rounds

Depends on how you are going to shoot those 100 rounds. If you plan to burn them as fast as you can, then a M4 type chrome lined barrel will help prevent excessive barrel wear. Certain barrel profiles also dissipate heat better.

Any barrel can handle rapid, excessive shooting. It's just a matter of how fast you are going to wear it out or do damage from overheating.

Keep in mind the AR-15 is designed to be an assault rifle not a light machinegun. In other words it was designed under the assumption that then end user would not be firing long and continuous bursts of automatic fire so its not going to stand up to harsh use as long. If you use it in the manner it was designed for it will last a long time. If you are using the drum magazine to simply eliminate the need to reload every thirty rounds you should have no problems. However, if you are gonig to try to bumpfire, or shoot through that 100 rounds as fast as possible you are going to accelerate wear on the barrel. Good Luck.

Most of the better barrels are full auto rated and made of Mil-spec certified 4150 chrome-moly vanadium steel. If an M249 on full auto won't burn it out I doubt you doing 100 rd mag dumps on semi will.