Quick question for the folks smarter than me.

Bought a new 9mm Shield with the intent to carry. Went to the range today to shoot it to make sure it behaved well and to try the defensive ammo I bought to carry with it (Hornaday Critical Defense). Shot 100 rounds of Remington 115gr FMJ to start and it all fired without a hitch. 4in groups at 20' (when I didn't pull the shot). After that, I shot 14 rounds of the Hornaday and they grouped about 6" left of where I was aiming.

Has any one else seen this? I know long guns can be picky about ammo, are pistols the same way?

Long winded question to get your thoughts, thanks.

Yes they can shoot to a different location than where the sights are aimed.  It is possible for different bullet weights to print high or low depending on weight and velocity.  Generally most Handguns  hit close enough to point of aim for self defense.  It is possible you were the cause of the gun shooting left, fatigue or anticipating recoil.  The rear sights can be changed for a particular load but I always tried to zero my pistol for my self defense load.

Mine hits right above the front sights with most ammo. The last range  trip my 115 gr reloads were about an inch above that and it low and left if I mess up.

a friend and i both had problems with this ammo(poa,fte,etc). poa returned to normal when we switched ammo
he uses critical duty and I use fed HST's or speer gold dot

EVERY BARREL IS PREJUDICED.

pistols and rifles.

I tried 9 different brands and weights of SD ammo with my Shield 9mm. I finally settled on Gold Dot 124grn.  They hit to POA all the time and shoot fine thru my Shield 9mm. They are still an excellent SD round. Each gun has it's likes and dislikes for ammo. Find one that shoots good for you and stick with it. There really is no magic bullet for SD.