Got to look at 3 things. Make sure that rifle is unloaded first.
1: look at rifle. You need to see if that handguard isn't loose or un-supportive on the end. There's a lot of weight up there, where the Bi-pod is, if that Handguard is loose or has any flex in it. Take rifle's barrel and "Point at you". Now grab hold of barrel with one hand and Handguard with other hand, and see if Handguard moves––even the slightest. If so, that needs to be tightened down, or screws "loc-tited" if they're loose. Anything to take out slop. Do this test again when done. This also checks if barrel is loose too, and if you notice wiggle in it. If Handguard is flexing/won't tighten up, you need to change out to better/different Handguard for better support and also for Bi-pod that puts stress on barrel from the underside.
2: I like those type rails that extend out over barrel, as it clamps down onto the barrel(in this case the handguard tube), and makes everything as "one unit", if this is the type you have mounted. However I don't like the height of them in this case––-a rail on top of another rail(weak link), which in this case, sets that scope pretty high on that rifle, when you need a scope mount system that keeps things more close together. So that might need to be changed out to bring scope closer to centerline of rifle. Lots of things will not let a scope adjust correctly to rifle, and you need to find that "Weak Link" and correct it.
Here's a cheap way to try and get that rifle better on target. You need a "Lazer Bore Guide" it's lots easier. Now aim rifle/lazer to put centerline of bore on Bullseye. Once done look at scope. How far off is crosshairs? I don't look so much at Elevation, as long as it's in a straight line and slightly above Bullseye. However, I DON'T want it more than 4" over Bullseye. This can be adjusted out when you get to distance you'r shooting at.
I look to Windage, and get that lined up AND onto Bullseye. If scope just won't adjust properly you have problem with it, OR, in majority of cases your scope mounts, as you have an alignment/mounting issue with them. Don't know ACOG's adjustment range. Usually Windage won't be more than 2-4" off, if good Centerline base drilled correctly and a properly centered scope used.
3: If shooting Factory Loads, that rifle will let you know what it likes, so you need a variety of different Manufactured ammo to test with. Trust me, you'll know right immediately, which rounds it likes by it's Grouping, using a 3 shot test of each ammo. But, do it slowly, as you don't want that barrel to get hot, as that also will throw off your shots. If doing handloads, you need to play with powder charges, primers, bullet weights and bullet tip/tail differences to find what that rifle likes––-just like Factory ammo. Lots of things go into an accurate rifle than people think. Hope this helps and keep us informed of results.
Del