I am just getting into long range shooting. I just bough a vanguard in .243 with a 24" barrel to use as my kill everything gun. I have a MarkV in .308 with a plain synthetic stock and a 20" barrel. when i bought it i liked the shortness of it for hunting in the hills of VT. Since then I have been looking in to longer shooting..
What would be the best rout to take with my rifle. id like a new stock. something a little more tactical but still preacitcal to hunt with. and a new longer barrel. 24" or 26". im not looking to spend 1000s, i need to save money for good glass. should i buy a new rifle or turn the one i have now into what i want. If its best to rebiuld my current markV where should i start looking.
MarkV is a great action to build off of. I would keep it and have it trued up. The 20" .308 will be a great teacher until you are ready to sink your teeth into something a little more substantial. I have 2 .308's, an 18" bull barrel, and 28" Varmint contour. Look into a Bell & Carlson stock.
Your .308 in a 20" will get you to 1000yd with a 175 bullet of some type. If you want a little more horse power, then have it reamed to a 30-06.
"Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it.  But small is the gate and narrow the road that leads to life, and only a few find it.
If you find your self in a fair fight, your tactics suck!- Marine 1st Sergeant Jim Ryfinger
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If you can afford it, replace the stock as Tank suggested. Otherwise, bed and float what you have.
Have the trigger tuned, or replaced.
Mount a 20MOA rail and good optics with repeatable turrets.
Get a good range finder capable of actually ranging deer as far as you intend to shoot.
There are lots of threads and articles here on each of these topics and you'll need to do all of these things to have consistent long range success. ...even if you rebarrel.
I gotta say, this is the most sound and straight forward advice I have read on this sight since I have been reading and posting on here. Hand Loading is the one key to shooting long range. Furthermore get a chronograph. Even the cheap ones will give you good readings on standard deviation and extreme spread of your ammo. The cheaper ones do not give the most accurate raw velocity readings but they will get very close and ES/SD is going to be the key anyway when looking for a long range load. There are a lot of the less expensive factory rifles capable of very good accuracy with a good hand load, in cartridges that are capable of very long shots. Factory ammo is where major accuracy issues normally come from with factory rifles. There are even a few quite expensive factory rifles that will not shoot well with anything (Kimber Light anything for instance) . You just usually have to find a load the factory rifles like. Where most good custom rifles will shoot acceptably well with a larger variety of ammunition. If you want a factory rifle that will be closer to the accuracy of a custom, then Your weatherby, Steyr SBS, Tikka, and actually the Marlin X series comes to mind. Remington 700s will usually like something extremely well and shoot with match rifle accuracy with one load yet the next load will have trouble shooting 2moa. Sorry about the long winded post, just thought maybe I could help with your dilemma by pointing out the importance of factors other than your rifle that will greatly improve your capabilities with your current equipment. None of this will be possible without a good trigger and good glass as mentioned above.
I am in a very similar situation as you, 1ton. I'm working with a Vanguard in 7mm RM for LR hunting.
First......GET RID OF the factory stock if it's synthetic. I tried to bed mine twice before the bedding compound actually adhered to the stock on attempt number three. And YES, I cleaned it thoroughly with brake cleaner and roughed up the surfaces each time. Now I'm buying a B&C Medalist from a member here on LRH. As soon as it comes in, that factory stock is going to finally go to it's rightful home---the trash can.
If you want to spend a little more dough, I'd highly recommend a Timney trigger. In my opinion, there are very few variables that contribute as much to one's ability to shoot well, as a good trigger does.
That's my input on specific Weatherby items. Of course I'm speaking about the Vanguard model. I've never shot a MK V or MK V Accumark.