Eric
A few difference's that I'm aware of are the personal attention spent on each call... mind you the Field Grade calls are very good quality calls for the money... but the Woodhaven Stinger Pro Series and Signature Series calls all get Mike Pentecost's special attention. In other words... Mike takes the time to mic each piece of latex for exact true thickness... and hand stretches each piece to an exact standard. Also... alot of the different colored latex's (red, orange, yellow, green, & gray), as well as prophylactic, are used in the Woodhaven Stinger Pro Series and Signature Series calls that aren't used in the NWTF Field Grade Calls.
The NWTF Field Grade calls are a good way for Woodhaven to expand in a more cost-conscious way while "passing it on".
I'm sure Mike and/or some of the other Sting Team members may comment further on this."You pay your dues for every gobbler" - Denny Gulvas