Many will say my 270 Allen Magnum would be redundant since you already have a 7mm STW but to be honest the performance gap between the two are so wide they are really in different performance classes.
I designed my 270 AM for exactly the purpose you are looking to use it for. 500-700 yard deer hunting with the most extreme performance you can get without getting into exotic receivers and ammunition requirements. There are no conventional factory rounds that will run with the 270 AM loaded properly, that being a 169.5 gr ULD RBBT Wildcat Bullet loaded to 3300-3400 fps depending on barrel length. This bullet has a BC of .740 on average in my rifles. If you run those numbers it becomes clear how impressive this round really is.
Yes, you can get factory rifles such as the 7mm RUM and 300 RUM and 30-378 to come close to this performance with the right bullet selection but with each example you have to use MUCH heavier bullets to get this class if BC if its even possible. In the 7mm family of bullets you will need to use the Wildcat Bullets or some of the other custom bullets to get this level of ballistic performance and most are over 180 grains in bullet weight. In 30 cal you will need +240 grains of bullet weight to get this level of ballistic performance and then velocity is limited in both calibers as well. If you have similar BC values but less velocity you still have less ballistic performance.
Another bonus of the 270 AM is that with the 169.5 gr ULD RBBT, its about as much performance as you can comfortably handle for most people in what I would call a packing weight rifle, espeically if you are opposed to muzzle brakes
. If you do not mine brakes, there are no issues and you can build very light weight rifles.
Now, I am not saying the 270 AM is the best choice for your needs, only saying its the highest performance round you will likely find that is practical for your purpose. Kind of the top level of the performance classes in deer rifles.
TO be honest, for deer out to 500 to 700 yards, anything from a 6.5-284 class round on up will work give you put the proper bullet in the proper place in the critter. Things to be considered are that the lower the level of performance the more critical range estimate needs to be as well as wind doping. Simply put, less margin of error.
There is never a large margin of error even with rounds like my 270 AM at 700 yards, you need a good set up and you need to know the conditions to make a quality hit on big game.
Main issue I see is your buget limitations. For a custom rifle
, this will not quite make it. For converting a factory rifle you already own you should have the money but unforunately the Wby MkV is not he best platform to start from.
I know that comment will raise some eye brows of wby owners and it is not ment to start a fight. Simply stating ask any top end accuracy minded gunsmith what their two favorite receivers are and I would guess you would only hear Wby mentioned a couple times out of every 100 smiths. There is a reason for this.
They are hard to get conversion parts for, they are limited in the amount of accurizing you can perform on them and on average, there are around 10 to 15% of all Wby rifles out there that simply will not hold under 1 moa no matter what you do with them as far as machining and rebarreling. That is simply a well known fact unoung accuracy minded smiths.
We will take a Rem 700 every time over a Wby if given the choice to work on for an accuracy rifle.
Just my 2 cents worth.