Well I have been reading and learning from this sight for a year now and have decided that it is time to build a true LH hunting rig. I was convinced that it was time after this years Mule Deer hunt in west Texas, I managed one mule deer at 619 yards then the next day a soild hit on a Whitetail at 678 yrds both one shot kills. So the light went on and it is time to get set up and practice to attempt a 1000yrd shot on game. The rifle I used was a remington 700 sendaro in 300 win mag shooting 175gr bergers, only mods are it is beded into a mcmillian classic stock, the scope was a leupold 4.5-14x 40 lr with fine duplex reticles. Untill this year i was comfortable shooting to 400 yards at game, I had practices all year at 500 yards with this rifle untill I could hit a 4"x 6" steel first shot every time. what should be my next step??
Stay with the Win Mag, go to a 200+grn. bullet and upgrade your optics. You might be able to get turrets to match the click values on your current scope and learn how to shoot at farther distances. You might want to try the Berger, Sierra, JLK 210 VLD's or the 208 A-Max. These bullets will stretch that Win Mag out to 1000yrds for deer very easily. You need to be able to push these things at 2950+ to get that far. The 190 Berger, JLK or the Nosler 200 Accubond would also work good for this application.
You may want to put a break on it so that you can spot your shots and handle the heavier recoil. Finally, Practice, Practice, Practice, at the distances you plan to shoot.
"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
Friends don't let friends develop canonitis!-chucknbach
arguing over the internet is like the special Olympics....even if you win, you are still...special!
Good job on the two kill shots you made. That's impressive without a doubt. By your post I can't tell if you are trying to say you are wanting to "build" a new rifle and you are looking for suggestions, or if younare asking for instructions for additional practice out past 600 to 1000 yards. From what you described you already have a good rifle that you could build off of. I agree with tank that you might want to go up to a lil heavier bullet since they handle the wind a lil better at longer distances. Honestly there is nothing wrong with the entire setup that you have now as long as you'll retain enough velocity with the load you have for proper expansion at the distances your wanting to shoot. If you like the current setup you have just spend some money upgrading your optics. If you really wanna build a true long range rig then jump out there and build a .338 with a good 28 inch barrell plus a good break added to that with a nightforce 5.5-22X50 scope and set it all in a Mcmillian stock and rock on out there buddy.
One thing to do is to get the trigger adjusted down to about 2 # and if it won't adjust or does not feel right then get an aftermarket trigger.
Depending on what you gear you already have I would leave the scope alone for a while and instead concentrate on rangefinders, wind meters, binoculars and spotting scope. There is no point in dragging the rifle out of the truck if you aren't going to be able to spot a deer and get prepped for the shot.
Finally, I would make sure my reloading technique and equipment were up to the task of producing high quality ammo. Such things as concentricity gauges, and precision seating dies may need to be purchased.
There is a lot of costs associated with longrange hunting besides the rifle.
Buffalobob has given some good advice. Alot of people just focus on the rifle itself, just as I did in my reply to you, however there is more to it than just te gun. I just assumed that you were reloading your own ammo and most everyone has a rangefinder it seems like these days, but it may not be a quality one for such a great distance and even if it is the beam width is going to be extremely wide therefor creating room for error. If your loads are working well for you at 600 yards then there is no reason not to try them at greater distances before you to to "fix/better" something that may be working just fine. Just go out and shoot! That's the best advice that anyone can give you. Go out and shoot and see what your equipment doesnat those distances and get to know it well.
Remember the movie Full Metal Jacket? "This is my rifle, there are many like it bu this one is mine!". Does your Sendero have a name? Betty? Suzie? LoL!!!
Good luck with your shooting sir.
The equipment that I have so far is the rifle remmington sendero with mcmillian stock all factory other than that. other equipment that I have is a leica 1200 range finder, leupold 10-20x40 compact spotting scopeand nikon 10x42 premier binocular. I do reload for this rifle I have competion dies rcbs I can can check concentrics of loaded roundseasy enough. I have been think if I should have an accuracy job dont to the rifle or should a rebuild be done? will the above equipment work or should I begin to aquire some thing else? which muzzle break should I conceder.
Using the system (Components) you now have and start stretching out towards the 1K mark.
Remember as the distance goes up the level of quality, effort, etc goes up somewhat exponentially. Your most important friends will be self control and discipline, attention to shot consistency recording of each shot. Recording shots keeps one from burning out the barrel too fast.