An unfinished AR upper made from a 60% Beryllium alloy is being sold on GunBroker. Dr. Strange gun pointed out that Beryllium is toxic. Machining and finishing it off could cause Berylliosis, a chronic lung disease that has no cure.

Even handling it could be have unpleasant side effects. According to wikipedia:

Beryllium contact with skin that has been scraped or cut may cause rashes, ulcers, or bumps under the skin called granulomas.

Scary stuff, considering the buyer may not be aware of this.

The 60% Beryllium upper.

The auction description is:

60% A1 BERYLLIUM UPPER, YOU WILL NEED TO REAM FRONT TO REAR THE CENTER TO FIT THE BOLT , DRILL FRONT AND REAR TAKE DOWN PIN HOLES,EJECTON PORT DOOR HINGE PIN HOLES, ROLL PIN FOR THE FWD ASSIST, AND THREAD THE FRONT FOR THE BARREL NUT…..S/H…10.00