AR/.223 trajectory mystery

[LeverGunJunkie]

Long time since I've last been here, but I need to turn to the High Road for assistance.

I mounted a scope on a DPMS Sportical (5.56/.223) and went to sight it in with some Remington 55 gr FMJ. This rifle always shot well at 100 yrds or greater for the previous 5 yrs before I mounted the scope. At 25 yrds, I adjusted in 4 rounds, and shot a confirmation group at 1" high. Thinking that was ok, I moved back to 100yrds to refine the sight in. However, I fired 5 rounds, all LOST. Missed the paper (8x8" target) completely. I cannot ascertain POI. High is all I can guess. But shouldn't be that high.

Scope adjustments corresponded to movement of POI. Scope seems fine, but since it is the only variable in this situation, I don't know for sure.

For the sake of discussion, let's assume I know what I'm doing. Am I missing something about the .223 Trajectory?

 

[Master Blaster]

Its the scope or the scope mount. What brand scope is it?

 

[Jackal]

Just sight it in and see if it holds zero. The ballistics have not changed, your scope is the culprit. Also, how high is the centerline of your scope over the bore? If its taller than the irons, that could explain some of the deviation.

 

[HJ857]

With a 100 yard zero it should hit low at 25 yards. That difference should be scope's height over bore distance, which is likely to be around 2 to 2 3/8 inches or something like that. If you're high at 25 yards, it'll be even higher at 100 yards.

 

[gonefishin1]

I shoot 2 inches low at 25 yards. Dead on at 100. But I have a high scope mount on top of my carry handle

 

[jmr40]

Scopes mounted on AR's are much farther above the bore than on standard rifles. Even with iron sights a 25 yrd zero will be 5-6" high at 100, 2-3" high at 200 and zeroed again at 300. A scope is even higher. You are shooting over your target.

You should be using a larger target than 8X8. I typically use a sheet of poster board or large piece of scrap cardboard behind my targets when getting zeroed in case something wierd happens. I'll always find bullet holes even if I'm off by a foot or more.

 

[556by45guy]

If you zero at 25 yards you'll be about 6 to 6 1/2" high at 100 yards, or somewhere thereabouts. If you sight in about 1.6" low at 25 yards you should be close to zeroed, or at least on paper, at 100yards.

With the muzzle velocity and BC it is pretty simple to make a trajectory chart/table.

 

[LeverGunJunkie]

Wow. Stepped away for lunch, and did not expect the awesome number of responses. Thanks.

The scope is an older Bushnell, 1.75-5x20mm. A friend gave it to me when her husband passed away. It has never been mounted, and was still in the factory bubble wrap when she gave it to me. It is mounted in the Burris PEPR mount, on a flat top.

I was shooting with a ply wood background that was fairly used. This made it hard to discern where I hit. Never had a problem hitting an 8x8" square before, and didn't think I would this time.

I think you all are right: Shooting high & potentially the scope is bad. Usually a bad scope won't respond to adjustments, this one did fine, and I figured it was ok. I'll give it another shot using your advice. Appreciate the help.

 

[rcmodel]

As you noted, you are sighted in 1" high at 25 yards.
Which corresponds to about a 450 yard zero.

As a result your rifle is shooting about 11" high at 100 yards.

Re-zero at 25 yards.
But this time adjust it to shoot about 1 1/2" low at 25 yards for an approximate 100 zero.

rc

 

[LeverGunJunkie]

rcmodel: Thanks. That clarifies things even more. I'll try and give it a shot as soon as I can.

 

[adelbridge]

We don't know what height rings you are using but I am relatively certain you are shooting over your target. Sight in 4" low at 25 yards and aim for bottom of target.

 

[JohnhenrySTL]

In my experience, a 25 yard zero is tough to deal with as far as scoped, high powered rifle cartridges are concerned. I only shoot that close at indoor ranges and to be "on paper." Last fall I was sighting in my new m-700 and had the same problem you are having. I was barely high a 25 yards, enough to take it out to 100. It was getting dark, I wasnt even hitting the softball sized orange target at 100 yards. Two frustrating weeks later, I was able to shoot it again, realizing I was like 8 inches high at 100 yards. I recommend a hundred yard zero, then checking it a 25 to see where you are at.

 

[sirgilligan]

As pointed out, you should be low at 25 yards.

Here is an example.

To be approximately 1" high at 25 yards means you are zeroed at 480 yards.



Crosses zero at around 18 yards.



Almost 1" high at 25 yards


9.8" high at 100 yards


Dropping like a rock at 480 yards. You might hit the varmint in the top of the head!

 

[sirgilligan]

A 100 yard zero is like this:



About 1.5" low at 25 yards



Nice and flat at 100 yards

 

[sirgilligan]

Here are the results of the report:


Firearm : Colt .223
Configuration Description: Factory Setup
Zero Distance: 100
Sights:
Sight Height: 2.5
Twist Rate: 0 IN 0
Righthand Twist
Configuration Caliber:
Barrel Length: 0
Barrel Type:
Ammunition Make: PMC
Caliber: .223
Type: FMJ-BT
Name:
Weight: 55
Ballistic Coefficient: 0.241
Muzzle Velocity: 3200
Powder Grains: 0
Overall Length: 0
Lot:
Notes:

Range: 1 yds Vertical: -2.5 inches
Time of flight: 0.00 seconds
[Velocity: 3196 fps] [Energy: 1247 ft-lbf]

Range: 2 yds Vertical: -2.4 inches
Time of flight: 0.00 seconds
[Velocity: 3191 fps] [Energy: 1244 ft-lbf]

Range: 3 yds Vertical: -2.4 inches
Time of flight: 0.00 seconds
[Velocity: 3187 fps] [Energy: 1240 ft-lbf]

Range: 4 yds Vertical: -2.3 inches
Time of flight: 0.00 seconds
[Velocity: 3183 fps] [Energy: 1237 ft-lbf]

Range: 5 yds Vertical: -2.3 inches
Time of flight: 0.00 seconds
[Velocity: 3179 fps] [Energy: 1234 ft-lbf]

Range: 6 yds Vertical: -2.2 inches
Time of flight: 0.01 seconds
[Velocity: 3174 fps] [Energy: 1230 ft-lbf]

Range: 7 yds Vertical: -2.2 inches
Time of flight: 0.01 seconds
[Velocity: 3170 fps] [Energy: 1227 ft-lbf]

Range: 8 yds Vertical: -2.2 inches
Time of flight: 0.01 seconds
[Velocity: 3166 fps] [Energy: 1224 ft-lbf]

Range: 9 yds Vertical: -2.1 inches
Time of flight: 0.01 seconds
[Velocity: 3162 fps] [Energy: 1221 ft-lbf]

Range: 10 yds Vertical: -2.1 inches
Time of flight: 0.01 seconds
[Velocity: 3157 fps] [Energy: 1217 ft-lbf]

Range: 11 yds Vertical: -2.0 inches
Time of flight: 0.01 seconds
[Velocity: 3153 fps] [Energy: 1214 ft-lbf]

Range: 12 yds Vertical: -2.0 inches
Time of flight: 0.01 seconds
[Velocity: 3149 fps] [Energy: 1211 ft-lbf]

Range: 13 yds Vertical: -2.0 inches
Time of flight: 0.01 seconds
[Velocity: 3145 fps] [Energy: 1208 ft-lbf]

Range: 14 yds Vertical: -1.9 inches
Time of flight: 0.01 seconds
[Velocity: 3141 fps] [Energy: 1204 ft-lbf]

Range: 15 yds Vertical: -1.9 inches
Time of flight: 0.01 seconds
[Velocity: 3136 fps] [Energy: 1201 ft-lbf]

Range: 16 yds Vertical: -1.8 inches
Time of flight: 0.02 seconds
[Velocity: 3132 fps] [Energy: 1198 ft-lbf]

Range: 17 yds Vertical: -1.8 inches
Time of flight: 0.02 seconds
[Velocity: 3128 fps] [Energy: 1195 ft-lbf]

Range: 18 yds Vertical: -1.8 inches
Time of flight: 0.02 seconds
[Velocity: 3124 fps] [Energy: 1192 ft-lbf]

Range: 19 yds Vertical: -1.7 inches
Time of flight: 0.02 seconds
[Velocity: 3119 fps] [Energy: 1188 ft-lbf]

Range: 20 yds Vertical: -1.7 inches
Time of flight: 0.02 seconds
[Velocity: 3115 fps] [Energy: 1185 ft-lbf]

Range: 21 yds Vertical: -1.7 inches
Time of flight: 0.02 seconds
[Velocity: 3111 fps] [Energy: 1182 ft-lbf]

Range: 22 yds Vertical: -1.6 inches
Time of flight: 0.02 seconds
[Velocity: 3107 fps] [Energy: 1179 ft-lbf]

Range: 23 yds Vertical: -1.6 inches
Time of flight: 0.02 seconds
[Velocity: 3103 fps] [Energy: 1176 ft-lbf]

Range: 24 yds Vertical: -1.6 inches
Time of flight: 0.02 seconds
[Velocity: 3099 fps] [Energy: 1172 ft-lbf]

Range: 25 yds Vertical: -1.5 inches
Time of flight: 0.02 seconds
[Velocity: 3094 fps] [Energy: 1169 ft-lbf]

Range: 30 yds Vertical: -1.3 inches
Time of flight: 0.03 seconds
[Velocity: 3074 fps] [Energy: 1154 ft-lbf]

Range: 35 yds Vertical: -1.2 inches
Time of flight: 0.03 seconds
[Velocity: 3053 fps] [Energy: 1138 ft-lbf]

Range: 40 yds Vertical: -1.0 inches
Time of flight: 0.04 seconds
[Velocity: 3032 fps] [Energy: 1123 ft-lbf]

Range: 45 yds Vertical: -0.9 inches
Time of flight: 0.04 seconds
[Velocity: 3012 fps] [Energy: 1108 ft-lbf]

Range: 50 yds Vertical: -0.8 inches
Time of flight: 0.05 seconds
[Velocity: 2991 fps] [Energy: 1093 ft-lbf]

Range: 75 yds Vertical: -0.3 inches
Time of flight: 0.07 seconds
[Velocity: 2890 fps] [Energy: 1020 ft-lbf]

Range: 98 yds Vertical: -0.0 inches
Time of flight: 0.10 seconds
[Velocity: 2800 fps] [Energy: 957 ft-lbf]

Range: 99 yds Vertical: -0.0 inches
Time of flight: 0.10 seconds
[Velocity: 2798 fps] [Energy: 956 ft-lbf]

Range: 100 yds Vertical: -0.0 inches
Time of flight: 0.10 seconds
[Velocity: 2794 fps] [Energy: 953 ft-lbf]

Range: 101 yds Vertical: 0.0 inches
Time of flight: 0.10 seconds
[Velocity: 2790 fps] [Energy: 951 ft-lbf]

Range: 102 yds Vertical: 0.0 inches
Time of flight: 0.10 seconds
[Velocity: 2786 fps] [Energy: 948 ft-lbf]

Range: 118 yds Vertical: 0.0 inches
Time of flight: 0.12 seconds
[Velocity: 2723 fps] [Energy: 905 ft-lbf]

Range: 119 yds Vertical: 0.0 inches
Time of flight: 0.12 seconds
[Velocity: 2721 fps] [Energy: 904 ft-lbf]

Range: 120 yds Vertical: 0.0 inches
Time of flight: 0.12 seconds
[Velocity: 2717 fps] [Energy: 901 ft-lbf]

Range: 121 yds Vertical: -0.0 inches
Time of flight: 0.12 seconds
[Velocity: 2713 fps] [Energy: 899 ft-lbf]

Range: 122 yds Vertical: -0.0 inches
Time of flight: 0.12 seconds
[Velocity: 2709 fps] [Energy: 896 ft-lbf]

Range: 125 yds Vertical: -0.0 inches
Time of flight: 0.13 seconds
[Velocity: 2696 fps] [Energy: 887 ft-lbf]

Range: 150 yds Vertical: -0.4 inches
Time of flight: 0.16 seconds
[Velocity: 2602 fps] [Energy: 827 ft-lbf]

Range: 200 yds Vertical: -2.0 inches
Time of flight: 0.22 seconds
[Velocity: 2419 fps] [Energy: 715 ft-lbf]

Range: 300 yds Vertical: -10.0 inches
Time of flight: 0.35 seconds
[Velocity: 2074 fps] [Energy: 526 ft-lbf]

 

[sfed]

Did the same thing last week, mounted scope on an AR 15 sighted for 30 yards then shot at a target placed at the bottom of a 100 yard 5foot high 8 foot wide target stand. Then shot the bottom target at 100 and rounds were hitting approximately 12-13 inches high. I adjusted the scope down to adjust the POI about 13 inches and the POI was within 1/2 inch of the intended POI, then adjusted for the 1/2 high and 1/2 left and then the scope was dead on, Then I adjust back up the required amount to have a 200 yard zero then shot the targets placed at 200 yards and all POI were dead on. That was the easiest adjusting scope I have worked with. I got all the information from www.handloads.com/calc/ this is the best website for trajectory plotting I have found.

 

[LeverGunJunkie]

Man, you guys have been great. Thanks for bringing all of this info to the discussion. I'm pleased to hear that it is most likely not the scope. Damn things are to expensive to replace all the time.

 

[mtrmn]

I always bore-sight my AR's at 100 yds by removing the upper half and setting it up on sandbags. Just remove the bolt carrier group and look down the barrel, then adjust the scope to the same point of aim. But it MUST be done at 100 yds. This gets me on paper and I fine tune from there when I shoot it.