T/C Encore
25-06, 15.5†barrel
Winchester 25-06, 120 gr. Super-X® Positive Expanding Point

I got a friend that shot two deer this season, around 100 yds with the above set up. He said he made good shots on both, and I have no reason to doubt him. He was not able to recover either deer. He said he followed the blood trail until it ended. I’m not sure how long the blood trail was, but he told me he followed both until the trail stopped. One of the two took him several hours and ended up on the next farm before the blood trail stopped. If he indeed made good hits in the vital area, what do you think would be the cause of the lost deer? I was wondering if the bullet passed through and didn’t expand very much. I don’t know what the M.V. is. I will try to get him out to the range to check M.V. and his accuracy. Any thoughts would be appreciated.

A good hit with that combo should have dropped a deer like a lead brick. I can't help but think this is a case of either operator error or bullet failure. I tend to think that it was operator error.
I use the 25-06 in an Encore rifle, and a good hit puts them down.
Another strong possibility is that he did not continue the searches long enough. Without a solid lung hit, they can travel a good way after the blood trail ends. There is a possibility that they may still be laying out there.
Hope you get the problem solved.

I agree 100%. Your friend did not make good hits on either of these deer. NO WAY a properly placed shot would have ended like that two times in a row.