Re: nightforce ch1 vs np1
You are probably referring to a MOA base or rail. This can get involved so let's back up just a little.
Let's say your scope has 100 MOA of travel. While most scopes are shipped out with the crosshairs centered (with 50 clicks of travel up & 50 clicks of travel down), that does not mean they will be centered once you sight in and zero your rifle. Bore sighting the rifle will get you on paper, but then you have to fine tune it. Most shooters use a 200 yard zero (this leaves your point of impact approx. 2" high at 100 yds.). You would have dialed up (or used) approx. 1.25 MOA to get from 100 yds to 200 yds. Since I am never lucky enough to have a scope dead on at 100 right out of the box, I always assume I may lose a couple more MOA in elevation getting to my initial 100 yard zero. So, on a worst-case basis, By the time I get zeroed at 200 yds., I may only have 45 MOA of my initial 50 MOA of travel remaining. Still with me?
Now let's assume you are shooting a 7mm Rem mag, with a 180 gr. Berger VLD with a BC of .67 and a muzzle velocity of 2,900 fps (fairly stout load). Dropping this data into a ballistics program, it tells me that with this load combination, my 45 MOA should get me out to about 1,500 yards. I have found most advertised BC's are optomistic, so actual results may yield only a max dial up of 1,400 yds.
A 20 MOA rail is slightly higher at the front than the back. This cants the line of sight on the scope higher, forcing the shooter to dial down approx. 20 MOA to achieve the same zero at 200 yds. This provides us with another 20 MOA of upward travel, or approx. 65 MOA. At 1,400 yds we need to dial up approx. 5.25 to 6 MOA+ for every additional hundred yards further out we go. So the additional 20 MOA rail takes us from 1,400 yds (conservatively) out to 1,800 yds. Obviously, if you substitute the 7mm Mag in our example for a 308 Win, you will decrease your distance by several hundred yards. Likewise, a 7mm RUM may extend you max distance by a couple hundred yards.
Not to further confuse things, but you need to remember that when we are "dialing up", we are actually moving the internal crosshairs down. This forces the shooter to raise the barrel up slightly to keep the crosshairs centered on the target. So when we are talking about travel, we are increasing our "dial up" capacity by increasing the amount by which our internal crosshairs can travel downward.
So the first question that would come to my mind is: Will I ever want to shoot beyond 1,400 yards? If yes, then is the cost of the 20 MOA rail worth the additional 400 yds. I would gain ( 1,400 yds out to 1,800 yds)? Could I compensate in other ways by staying with a flat rail (1,400 yds. max) and then using the MOA stadia of my reticle for any addl. holdover required?
I hope this has answered your questions. To any one else reading this: if I have misstated or explained this concept incorrectly, please feel free to correct my post. I'm under-the-weather right now, and may not be thinking clearly.