Having problems sighting in my RRA

[Dss21]

I have a RRA flat top with a 16 inch barrel. I had a Konus 3-12x 50 scope mounted with a Promag one peice base. When I started to sight this in I got it on paper at 25yds. I then zeroed it at 50 yds. When I went to 100yds it shoot 2 inches high. I then went back and shot at 25yds and it shot 2inches low. The Promag base was very tall and had the scope setting well above the barrel. I thought with the scope center line so high above the barrels I should get some lower rings. I bought a set of Weaver 6 hole picatinney rings that got the scope as low as possible. I went out today and zeroed the new combo at 50 yards. I then shot at 100yds and was 1.5 inches high. I then moved to 25yds and was 1.5 inches low. Any idea what is going ? I am starting to think there is a issue with scope. I was using Federal XM193 ammo.

 

[IndyMonkey]

Yea, you need to figure out what the trajectory of the 5.56 is.

 

[Jack Ryan]

... I then shot at 100yds and was 1.5 inches high. I then moved to 25yds and was 1.5 inches low. Any idea what is going ? I am starting to think there is a issue with scope. I was using Federal XM193 ammo.

Sounds like you are in mighty fine shape now.

So this is yer first rodeo? How do you like it so far?

External Ballistics Calculator

 

[sloughfoot]

A lot of info to sift through here, but I will try. A 25 yard zero is virtually the same as a 200 yard zero. If you fire your rifle at 100 yards with a 25/200 yard zero, it will be about 2 inches high at 100 yards. This is good.

I have to admit, I got kind of lost with your 50 yard descripton. But, what you have to know is that, the bullet will not impact the center of the target no matter the distance, except for the zero'd distance.

The bullets path is not that of a laser, it is arcing constantly.

For GP use of your scoped AR, here is a suggestion. Get a 25/200 yard zero, your AR will then be 2 inches high at 100 yards, and 6 inches low at 300 yards. As long as this is close and consistant, you should be GTG.

Then again, your scope might be messed up.

 

[Dss21]

Thanks for the input. I understand that the path of the bullet is a arch and not laser flat BUT I expected it to be better than 3inches total in a 100yrds. When I looked at the Remington charts they had the .223 55gr 50yrds= -0.1 100yrds= 0.6 150yrds= zero 200yrds= -1.9 for a total elevation change of 2.5 inches in 200yrds. I thought it was odd that I had a total of 3 inches in 100yrds. I would of thought the xm 193 would of shot as flat as the Remington .223 loads. The reason for the 50yrd zero was most of the coyotes in the wooded area I have been hunting have been 50 to 75 yrd shots. Thanks again for the help.

 

[lovemywoods]

Here's a link describing three ways to zero an AR rifle. It focuses on using the iron sights, but much of that applies to glass optics as well.

AR-15 Zeroing

I prefer the 50/200 yard zeroing. If you zero at 50 yards, you're zeroed at 200 yards. For many shooting situatons, including for coyotes, this works well.

 

[Jack Ryan]

... When I looked at the Remington charts they had the .223 55gr 50yrds= -0.1 100yrds= 0.6 150yrds= zero 200yrds= -1.9 for a total elevation change of 2.5 inches in 200yrds. I thought it was odd that I had a total of 3 inches in 100yrds. I would of thought the xm 193 would of shot as flat as the Remington .223 loads. The reason for the 50yrd zero was most of the coyotes in the wooded area I have been hunting have been 50 to 75 yrd shots. Thanks again for the help.

Well look at the last set of shots you mentioned in the OP?

You know you never did shoot the yardages you are comaring it to, at least you didn't list them in the OP. You can't shoot 25 and 250 yard targets and then wonder why they don't duplicate 75 and 150 yard shots.

Did you even look at the ballistics and trajectory link I posted? There is a lot more to calculating trajectory than just looking on the back of a box of shells, duh? One that's not been mentioned once is the distance from the center of the scope and the center of the bore. A little more than "really high" is required for any thing more relevant than " really cool " comentary here.

The biggest problem people have when trying to zero a scope is no matter how much trouble they have or no matter how much amo they've wasted they just don't listen. "Duh right, thanks a bunch, I didn't know that, now I'm gonna just go back and do whut ah always do..."

 

[IndianaGTI]

Thanks for the input. I understand that the path of the bullet is a arch and not laser flat BUT I expected it to be better than 3inches total in a 100yrds. When I looked at the Remington charts they had the .223 55gr 50yrds= -0.1 100yrds= 0.6 150yrds= zero 200yrds= -1.9 for a total elevation change of 2.5 inches in 200yrds. I thought it was odd that I had a total of 3 inches in 100yrds. I would of thought the xm 193 would of shot as flat as the Remington .223 loads. The reason for the 50yrd zero was most of the coyotes in the wooded area I have been hunting have been 50 to 75 yrd shots. Thanks again for the help.

That is if you are talking about ddrop from the end of the barrel. You are shooting the bullet upward to hit the target at 50 yards unless your sights are 0.1 inches above the center of the barrel. since you are shooting your gun upward, it will continue to climb until its drop equals the amount it was shot upward. Think of a triangle with the top side flat and level. That is your line of sight. The bullet is coming up to meet that line of sight at 50 yards.

 

[42769vette]

just fyi take the ballistics on the box of most factory ammo and forget about them. they are usually optomistic to say the least. usually real world testing proves them wrong. they will get you on paper but thats about it in my experiance

 

[Dss21]

I had time tonight to put the numbers in the ballistic calculator Jack Ryan posted and I was real close to what it came up with. As stated above the manufactures numbers are not very close.