The 300 Extremes were stainless steel.

I have been trying our the VPA 160 glue on.  Have not shot anything with them yet but like the head.  Can anyone tell me what differences there are between the 160, 190 and 250 grain glue on?  What do they do to make up the weight difference in these heads?  I picked up a few of the 160 on a trade but can move up to the 190 and still get the same weight so I am curious of the difference.  
Thanks
ALDO

The only dirrerence I have been able to see is the thickness of the blades and maybe just a bit of ferrule depth.  The length and width are the same.