Best Hunting Bullet past 300yds ?

[Bassfish1952]

For the second pic, is that morning or afternoon?  If that is the one where they are 300-350 I would look for a tree/bunch of trees about 100-150 yds away from where they come out.  So about 200 yds downrange from that box blind.  My experience (which I confess is NOT decades) has been that at 100+ yds the deer won't get spooked by scent or anything.  Set up in the shade close to or partially hidden by the trees.  As long as the wind is not coming from your back you should be good. 
If you can set up the day of or the day before, watch the weather forecasts for wind speed/direction, that way if you have to set up on other side of that narrow, open run.
Rhino has some pretty good little popups which I used this last fall.  (I try to walk things in on a small hand wagon which lessens my approach-footprint.)

This is a pay deal . I started by going to a school funding event , Money went to the school Landowners were students parents or friends . You were put into the stand and didn't come out till they got back to retrieve you. Now I have gotten in with this guy, Family owns 3500 acres , he has blinds set up and first couple of times it was the same but after going a few times it has gotten more relaxed. I found out another of his customers had bought a blind and brought portable blind with him when he came . Found out by meeting him this last trip. 
14 degrees is cold for me so I go into a box blind in the morning and a tree blind in the afternoon , brown grass and the wood front is the box, that is where I got my 3 this last trip. Tree blind is the green with the s curve road I got 1 there in Dec. 
He had a tree blind in the tree where it narrows down but moved it to where it is now because of a change in deer movement  and starting to have a problem with hogs 
We'll see I like going there , much cheaper than buying property and I don't have to do anything . We meet in the morning I am taken to the blind then around 10am I get taken out and return around 2pm to go back in for the afternoon 
The box blind has a  window sill to steady the rifle works great for me but the tree stands just have a 1" bar that goes in front of you so it's either offhand shot or I have to bring a shooting stick or some kind of steady. 
All in all for me it works very well and allows me to still get out . 
I went with my grandson on a hunt in Georgia this year , his boss owns property up there . So it was here's the property here is where there are some  blinds go hunt. We walked in that morning but that afternoon I ended up driving to within 50yds of the blind and after he shot his deer we drove my car down to get the deer. He would have done ok pulling the deer out but I would have not made it . LOL