Some folks are much more prone to doubling than others are. Have a brother in law that does it almost every time he fires an M1 Garand.
As noted its not really a trigger issue, other than you may not be able to use it as set, you may have to set it differently.
Not all that uncommon at times actually from what I've seen. And tuned up single stage factory triggers were worse about it than anything I've seen on the AR.
