Ruger Ar-556 Trajectory Problem

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Howdy,

I have a Ruger Ar-556 that has me perplexed. It is all stock except a 3 lb CNC aftermarket trigger and free float handgaurd. I have a Vortex Crossfire 3-9x40 mounted on it. The rings are fairly tall (3 inches from center of bore to center of scope) for me to get a good sight picture/cheek weld. Everything is tight and the gun cycles just fine.

The other day I worked up some handloads with 77 gr tmk bullets. From what I have seen online/loading data, I estimate they are traveling about 2500-2600 fps using 24.4 gr of VV N540 and CCI 450 primers. Of a bipod, I am shooting sub 1 inch groups with the best being 0.70" at 100 yards. Ballistic calculator says 0" at 50 yards, 1.8" high at 100 yards and again 0" at 200 yards.

I sighted it in dead on at 50 yards this morning. At 100 yards, the bullets strike 2 inches high which is about what I expected. Now at 200 yards, I was expecting them to be dead on or no more than 2" lower than the point of aim. However, at 200 yards, the bullets stuck the target 4 inches below the point of aim. That is a 6" drop from 100 yards to 200 yards. I have also experienced this with other loads (Frontier factory ammo with a 68 gr hollow point and 77 gr tmk handloads with H322) which acts in the same way. This happens both off a shooting bench and prone.

Another thing I should also mention is that something has changed but I do not know what it would be. When I was shooting it back in the spring with the 77 gr tmk handloads with H322, I had it sighted in dead on at 200 and 2.5" high at 100 yards. Since then, I did nothing to the gun and now it drops low at 200 yards.

What do you guys think could be wrong?

Just out of curiosity; what were your group sizes at 200 yards when zeroed at 50 yards?