If it was me I'd go with factory ammo from your local store.
I was loading some ammo that was just under +P as my revolver wasn't rated for anything higher. I was supposed to be in the 900fps range and when I chronied it found out the velocity was in the 660 fps range. Wasn't sure for the reason if it was old powder, bad crimp, old primers, excess barrel gap, oversized barrel... I was left with all those questions and a few more.
One thing I didn't do was increase the powder charge until I got the book velocity.