Re: remington, howa, tikka, browning(boss) & caliber
From a rifle standpoint, what you are asking to do can easily be accomplished with the 270Win and 150gr Ballistic tips, SST, or MK.
The problem is your lack of time to get properly set up, load test and practise. Buying a rifle with the accuracy does not mean that you will be able to shoot that well.
All of the production rifles you mentioned, have the potential to work. Just need time to work out a load and tune the rifle, scope, range finder, and drop table.
If you are not completely sure of what is going to happen when you pull the trigger, please stay within much shorter ranges for guaranteed hits. Long Range shooting is not about spray and pray...