Dave the travel needs to be barely far enough to cover the holes. Right now they are drilled at 1/4" and the travel is almost the same, I'll need to file the stops a little more I think other wise powder can trickle past the gates or the gates wont open all the way to fill the nipples.
The gates will be flush on one end with the housing but the spring end will get a thumb pad welded on.
Here is a shot of the spring material I use on many of my guns. I'm sure this is 1075 but I'm not sure. I called Brownells and they werent sure either. It heat treats really nice and consistant. hold at 1500 F for 5 minutes and quench in Brownells "Tough Quench" and they are always at 63 rockwell hardness. Temper for one hour at 725 F will give a spring temper of 50-51 rc.
I left a tail on these springs so I can test the hardness, they will be ground off later.
I use Brownells PBC for a anti-scale and never have trouble with scale. The scales just washes right off in hot water and Kayes new tooth brush.