Well, not quite the same MOA at the longer range. There are some funny exceptional situations, but most group opening is due to drift away from the trajectory at a rate that stays constant during flight for all practical purposes. Because the bullet slows down as it flies, each successive 100 yards has a longer time of flight, giving the bullet more time to drift a larger number of MOA.
I have a radar drag function for the 77-grain SMK. It says a muzzle velocity of 2750 fps will give it times of flight that are:
0.1148 s first 100 yards
0.1271 s second 100 yards
0.1412 s third 100 yards
So, MOA at 100 is expected to be 11% bigger at 200 and 23% bigger at 300. Bryan Litz compared that expectation with real results in his first book, Applied Ballistics for Long Range Shooters, and found actual spread slightly bigger than it predicts, probably due to things like atmospheric irregularities over the greater distance randomly adding to the spread.
Rebs,
By changing assumptions, 22.9 grains is another number I came up with. If you can measure the actual velocities you are getting a better estimate can be made. Also, you can run a velocity ladder and look for flat spots, which helps find the nodes. Just load 25 rounds in 0.1-grain steps from 21.7 grains (10% below maximum; 24.1 grains, according to Alliant's site), and record the velocity of each on and graph them, looking for flat spots. I can help with the graphing if that isn't in your bailiwick.
For seating length, you need to know how far forward of the bullet your chamber throat is. You can buy a tool for doing this, the Hornady Lock N Load Overal Length Gauge being the most popular one, or you can take an old case, split the neck with a hack saw, debur the cut and squeeze the split neck down and set the bullet just barely into it. Then push the case and bullet all the way into the chamber with your little finger and use a cleaning rod from the muzzle to gently push it out. That case and bullet should come out with a COL that just touches the lands. You can take your load down to 21.7 grains and shoot some loaded that long and some that are shorter in steps of about 0.02" all the way to about 0.10 inch shorter or to 2.260", whichever is deeper. At some point along the way, you will find a depth that produces the smallest group. Use that depth and step it through different loads to find ones that group even smaller until you find the smallest one.