That's not what you claim though. You imply he was mentally unstable when he bought the gun and you have no idea if that's true or not.
I don't think crazy people wake up and say, "I'm going to be totally crazy today".
But for the record.
2016 shooting of Dallas police officers - Wikipedia
On May 1, 2014,[76] during his deployment, he was accused of sexual harassment by a female soldier, who sought a protective order against him and said that he needed mental health counseling
The New York Daily News did an interview with a man who sold Johnson a semiautomatic AK-47 pattern rifle in November 2014. The man said he sold Johnson the rifle and made the deal in a Target parking lot.
So he was able to buy a military grade weapon AFTER he was discharged for mental health reasons.
As far as the SKS, yeah old school junk like that is not FA. Also, you are still trying to deflect and your dishonesty is typical. The killer did not use an SKS.
Most news accounts called it an SKS.. Other called it an AK-74,