Doubling with my M1A.

[SunnySlopes]

I've not fired this gun before now. I bought it new. The last magazine of rounds, every single time I pulled the trigger, the gun doubled. Prior to that, it doubled about half the time.

My son fired the gun. He couldn't get it to double.

I'm thinking maybe it's my form?

The exact same thing happens with my S&W M&P 15 Performance Center. Again, it doesn't happen when my son fires the gun.

Suggestions?

thanx