I can't be that bad of a shot

[Street Rat]

I took my M&P 15 out to the range and while I wait for the funds for a good scope, I was playing with a cheap scope, very cheap. I had it sighted in pretty good at about 25 yards, then went to about 75 yards and the results were not good. The target I was shooting at was about 16x20 with 5 red dots like the five dots on dice. At 75 yards I shot 30 rounds taking turns at each red dot. It was hot so I was not going to make several trips down range to check where I was hitting. Anyway when I retrieved the target, I had only hit it about 8 times, and they were all high as if I were aiming at the lower dots and hitting high just above the top two on each side. I've used the iron sights before at 50 yards and acutally surprised myself a little. What is my problem here, is it the scope? I know it's cheap, but I thought basicly, a scope is a scope.

 

[NikatKimber]

At 25 yards your scope and barrel are NOT parallel, since the scope is so much higher than the barrel, so the POI and POA will change significantly from 25 to 75 yards. If it is still sighted in at 25, then go back start at 25, then move back maybe 10-15 yds at a time each time readjusting the scope.

 

[338Shooter]

Worst case scenario if his line of sight is 3" above the bore then he is 9 inches high at 75 yards with a 25 yard zero. That is neglecting gravity.

Kinematics neglcting wind resistance, he should only be 8.045" high at 75 yards with a 25 yard zero and a muzzle velocity of 3200 f/s.

Sighting in at 25 is no different than bore sighting at 25. He should still be on paper at 75 and 100 yards for that matter. At 100 neglecting wind he's looking at 10.3" high. I guess that is enough to miss his target. Needs about 10.75 moa or 43 1/4MOA clicks for a zero at 75 from a 25 yard zero if my math is correct.

 

[Deacon]

At 25 yards your scope and barrel are NOT parallel, since the scope is so much higher than the barrel, so the POI and POA will change significantly from 25 to 75 yards. If it is still sighted in at 25, then go back start at 25, then move back maybe 10-15 yds at a time each time readjusting the scope.

+1

I'd sight in my irons as far out as is practical, then the red dot will be easy.

 

[NikatKimber]

That sounds about right. He did say that he hit it some of the time, just way high.

Had to go and get all technical on me huh?

 

[DrBaker]

Worst case scenario if his line of sight is 3" above the bore then he is 9 inches high at 75 yards with a 25 yard zero. That is neglecting gravity.

Kinematics neglcting wind resistance, he should only be 8.045" high at 75 yards with a 25 yard zero and a muzzle velocity of 3200 f/s.

Sighting in at 25 is no different than bore sighting at 25. He should still be on paper at 75 and 100 yards for that matter. At 100 neglecting wind he's looking at 10.3" high. I guess that is enough to miss his target. Needs about 10.75 moa or 43 1/4MOA clicks for a zero at 75 from a 25 yard zero if my math is correct.

Where are you getting this info?

A .223 in the AR platform should not have much more than around 3 inches of change from 0-300yards. If 0 yards is 0 inches then it will be around 3 inches high at 100 yds. 50 and 200 yds will be about the same height. 25 and 300 yds will be about the same height. After 300 it starts dropping really fast.


He is using a 16x20 target at 75yds after zeroing at 25yds. He has other problems.

 

[338Shooter]

Just math. It could be askew though.

 

[RyansFortyFives]

Don't forget to factor in the Coriolis effect...

 

[DrBaker]

Just math. It could be askew though.

I'm not an expert, but I have done a small amount of research on the .223. I think your figures might not be accurate for this particular round.

Again, I'm no expert. However, we want to make sure we provide accurate information as there are countless peeps who will be reading these threads and relying on what they find.

 

[338Shooter]

It depends on the distance of his line of site over the bore. I was using 3 inches. My numbers are good neglecting wind. These calcs figure in wind and I estimated the BC based on some bullets available from midway. Oh and thanks for the forum tip, I'm new at them.