Probably a grip issue. Headknocker has the right idea. Give that a try.
I like to reload my 642 by grabbing a second 642.
On the days that I carry just one, I use an HKS or S.L. Variant. I've used the Comp I's in past also. Just practice with what you use.
If using Speed Strips, try loading them up with two rounds, a space and then two more rounds for a total of four rounds only. Gets you back in the fight quick.