.40 S&W Handloads
I too have some feed problem experiences with .40's. I have 4 firearms in 40S&W and each can be a little finicky. Similar to what others have mentioned, like crimping and bullet seating, these two are the usual suspects. In my case, since I use a carbide crimper, the fix I have found is nearly always in bullet seating. Additionally, the shape of the bullet is a huge factor. For example, seating the XTP's is trickier than the FMJ's which have a more consistent shape.
What we found with XTP and Noslers is a larger variance by the bullet seater. In millimeters it could vary as much as 4 millimeters at the same setting on the bullet seater. So we simply take the bullet down a little further. Now, our reloads cycle in all the firearms just fine.
On crimping, I tend to crimp as little as possible especially in 9mm. The carbide ring should take care of any bulges going into the die. When we experimented between crimping and bullet seating - we kept crimping the same and seated the bullet deeper - nearly always, best we could tell, it was the bullet seating that made the difference on improved feeding.