Installing my first Winn grip: will it stretch as much as EVA, or do I need to ream it until it fits in place?

I ream them. Not worth the sweat and pain trying to stretch them into place. If using a fighting butt without a through hole, enlarge the hole by using a set of sharp drill bits. Find a bit that very snuggly fits the hole and turn until you hit the bottom, don’t cut through the end. Take the next size drill bit and repeat until you enlarge the hole enough to fit the butt end of the blank. Enlarging the hole this way kept the hole centered. It is quite easy to do and goes quickly
Norm

It will stretch but not as much as EVA due to the wrap of Winn Polymer. I would ream it to stop a couple of inches above where you want it to end up. Then push it into place. Another thing in the Winn grips is you don't need to use epoxy to hold them in place although you can. I use a two sided tape that is designed for golf clubs and I get it from Golf Works so I know it is good stuff. Wet the inside of the grip with mineral spirits and then pour the excess over the tape. Once you get the grip down the blank to the tape it will slide on rather easily. Let it sit a couple of hours and your good to go. IT will not move.
I had reason to remove a winn grip that was taped on and you can't believe how hard was to remove that grip.

Tom