Odd grouping/zero

[Newtothis]

So I bought some new 62 grain ammo, I was originally zeroed at 100 yards with 55 grain. The new ammo is dead on at 50 but is shooting a foot high at 100. Has anyone else had a similar issue? Does anyone have a solution? I can understand being an inch or two off with the 50 yard difference being iron sights and a cheap rifle, but a whole foot is insane to me.

Some info on the rifle (budget/beginner rifle)
- cheap American Tactical rifle
- 1X7 twist
- using Magpul Backup Sights
-62 grain M855 ammo
- shot same way using bench and offhand

 

[meketrefe]

So I bought some new 62 grain ammo, I was originally zeroed at 100 yards with 55 grain. The new ammo is dead on at 50 but is shooting a foot high at 100. Has anyone else had a similar issue? Does anyone have a solution? I can understand being an inch or two off with the 50 yard difference being iron sights and a cheap rifle, but a whole foot is insane to me.

Some info on the rifle (budget/beginner rifle)
- cheap American Tactical rifle
- 1X7 twist
- using Magpul Backup Sights
-62 grain M855 ammo
- shot same way using bench and offhand

Something has changed radically and it cannot be the ammo. Also have realistic expectations if you use backup sights.

So most likely it is your sights or your aiming when you think you are using the same reference and you are not.
Even with a diopter system will be a lot of training to account for any correction at 100 yards all the way to the 1-2MOA level so think
more like Minute of Plate with open/backup sighs. At 500 meters any hits in a human side torso are marksman qualification material
so take those measures 18x30 and divide them by 5 (3x6 inches) = 3 to 6 MOA and that is a good as you can expect ....and probably less
with backup sights that might or might not be that great.

 

[Vapor]

I would expect some poi shift, but not that severe. I tend to see more changes in radical grain weight changes in other calibers.( going from a 125 grain .30-06 to a 180 grain.)

I can't comment on the preciseness of magpul sights. I don't care for plastic sights myself. I usually use Sig or Troy sights, which I feel afford me more precise aiming and adjustments.


That being said, which sized apature were you using? Same for both loads/distances? Are your sights torqued down to the correct specification and the cross bolt is up against the rail section? Is the rifle free floated? If not, did the hand guard possibly have different pressure points than when you shot the 55 grain? Did your head/cheek weld maintain the exact same position?

Is everything on the rifle tight and correct?



If you do not understand some of what I just said, please let us know.

 

[Curmudgeon]

My first question would be about your shooting experience. If you're new, I'd probably say it's the shooter.

If not, we could dig deeper.

I'd also refer you to this video. Differences arent as great as yours, but there are some...

 

[Vapor]

Keep in mind as well with the height over bore of an ar15 style rifle, that a 50 yard zero is a 50/200 zero. It will be high at 100 yards. Usually by about 1.5-3 inches.

 

[thegatman]

How about rate of twist affecting the heavier bullet?

 

[dwa12479]

Keep in mind as well with the height over bore of an ar15 style rifle, that a 50 yard zero is a 50/200 zero. It will be high at 100 yards. Usually by about 1.5-3 inches.

This right here is my guess. The 100 yd zero means everything after that requires a holdover. Where a 50/200, anything in between will require a holdunder. 12" seems to be pretty high for just a 7gn ammo switch.

I've always preferred the 25/300 zeroing. Aim center mass and you're pretty well guaranteed some sort of hit... and I'm not a good enough shooter to be able to reliably go past 300 without magnification and a good benchrest.

 

[Darth]

My first question would be about your shooting experience. If you're new, I'd probably say it's the shooter.

If not, we could dig deeper.

I'd also refer you to this video. Differences arent as great as yours, but there are some...

Agreed.

When I was new and finally accepted myself as the issue, the problems started to diminish over time.

 

[Vapor]

Agreed.

When I was new and finally accepted myself as the issue, the problems started to diminish over time.

I used to be all over with peep sights. I could hit a gnats ass with v notch type.


Then I learned consistent cheek/head placement and to allow my brain to naturally center the post.


I can now hold 2" or less off of a rest with almost any AR with iron sights. I think I shoot even better with my peep sighted .30-30 ( this is probably due to how bloody long the sight radius and comfort.)


Something else I learned, stick to the same grain weight, and if possible, manufacturer of ammo.

 

[Celt]

Did your optic move? If you don't have the screws torqued down properly, your optic will move. If you shot it 50, and were at zero then go to 100 and you're a foot high, and go back to zero at 50 again and I have no explanation.

 

[meketrefe]

How about rate of twist affecting the heavier bullet?

Not sure I follow your thoughts here...

 

[Marine Cpl]

This right here is my guess. The 100 yd zero means everything after that requires a holdover. Where a 50/200, anything in between will require a holdunder. 12" seems to be pretty high for just a 7gn ammo switch.

I've always preferred the 25/300 zeroing. Aim center mass and you're pretty well guaranteed some sort of hit... and I'm not a good enough shooter to be able to reliably go past 300 without magnification and a good benchrest.

The 50/200 is a hit center mass all the way out to 250 yards. The bullet is within 3 inches up or down.


There is way more guess work at closer distances with a 25/375.

 

[Celt]

The 50/200 is a hit center mass all the way out to 250 yards. The bullet is within 3 inches up or down.


There is way more guess work at closer distances with a 25/300

I have this same image saved on my phone.

 

[Marine Cpl]

Just updated the image. This one gives you actual numbers.

 

[1075tech]

How about rate of twist affecting the heavier bullet?

Probably not OP's issue in this case, but possible. How are the groups? He says POI was higher than POA.

Was 55 grain 223 or hotter 556? What is the new ammo?

My old 1:7 shot 55gr 556 into a shotgun style pattern. 62gr 556 shot very well.

 

[dwa12479]

The 50/200 is a hit center mass all the way out to 250 yards. The bullet is within 3 inches up or down.


There is way more guess work at closer distances with a 25/375.

Guess familiarity always wins. I've gotten to know the holds with the 25/300 over the years, it's what I was always taught.

 

[Marine Cpl]

Guess familiarity always wins. I've gotten to know the holds with the 25/300 over the years, it's what I was always taught.

Same here. The 25 is a good all purpose zero for the military to reach out all the way to 500 with minimal holdover. But for us, the others completely take away all guess work until after 250. Probably even further if you aim for the head at about 300 or so.

 

[meketrefe]

Before one decides on the Zero the best thing is to understand:
A) At what ranges the most likely engagement scenarios are going to happen. Special forces zero at 100 yards and rarely shoot that long.
B) What ammo is one going to be using and what speed is being produced.
C) at what range we achieve the maximum probability not just to hit but the lehality of the round and based on the round and chosen projectily itself. If we are talking about the military 5.56 we should worry more about what happens within 200 yards as the lethality of the average round drops drastically past that range.
D) Zeroing at close distances is a bad idea as we cannot assume the zero at close ranges and consequent extrapolations will
actually work at a distance with the standard sights.
Over the years I have realized that the two zeros are not the same and that large large aperture groups with M16A2 at 300 yards (BZO as per Technical manual) yield 6-7 inches low and 3 inches high at 50 yards. Doing the extrapolation at 200 yards, the shot groups with large aperture
are 22-26 inches low and sometimes a foot off to the sides. In other words, most shooters coached by me or others would miss their targets so the Military and Internet theories and field manuals have their flaws and even quality time tested sights can be confusing to say the least.

IMO Good zeros are 100 and 200 yards because
1. they are distances adequate for most civilians and military based guns and ammo
2. most people have access to ranges to test those in terms of ammo and skills w/o assuming extrapolations. (actual spreads)
3. Also provide a good compromise within the range the typical guns and rounds are most effective and most likely to be used including both hunting and defensive use.

 

[GOPerfect]

You sight pattern is changing

 

[Vapor]

To summarize:

1. Check your sights. Are they tight/properly installed?
2. Think about your check weld/eye alignment. If not the same every shot, change that.
3. If rifle isn't free floated, be careful of pressure.
4. Try the 55 grain again. See if your zero for that had stayed the same. If not, and you have done steps 1-3, it's probably you.