Ar 15 bieng an inaccurate sh*t head?

my m&p15 is shooting low. like way low. like 1ft low at 100 yards kinda low i sighted it in at 25 yards. and it shot high about 8 inches at 100 yards. now its shooting low (all of this is at 100 yards) i shot 4 loads of reloaded ammo on the 5 targets on a grid target and they all showed up in one big hole in the middle of the target at 25 yards i couldnt get anything on paper at 100 yards. i would like to know why my riifle is ****in up. i aprecciate your time thank you. also its a sport so it doesnt have a chrome lined barrel if that makes a difference the reloads were shooting the same as factory ammo i shot the same day so its not them... i have a 6x optic by ncstar that my dad got me for my birthday. maybe its bent haha.