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Why are my POI groups at 50 yards out hitting higher than they are at 25 yards?

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M

m021478

Member
Nov 6, 2019
71
0
New York, United States
Trying to tune my Impact MK2 to shoot FX Hybrid Slugs and I’m having a bit of an issue that I don’t know how to deal with...

My groups at 25 yards out are dialed in and hitting the bullseye as intended. But when I try hitting a mark 50 yards out, the groups are consistently higher than the mark I’m aiming at (no changes made to the scope or gun). This suggests that the projectiles are rising the further out they travel (at least for the first 25-50 yards). Obviously the opposite is supposed to be the case. What would cause something like this to happen?

I using an FX Impact MK2 with power plenum (.25cal; 700mm barrel; superior liner)
 
M,

I don't have any experience with that particular gun, but what you described is very common with many guns and combinations. 

When one sights in at an indiscriminate distance, 25 yards as in your example, one of 2 things will happen. You will have a zero at 25 yards. As you described, at 50, the impact is higher than your 25. This means, at a point further than 50, let's say 75 for arguments sake, the impact will be the same as 25. This is totally normal for a zero that one wants at an indiscriminate distance. 

The second thing that COULD happen, is the distance of your zero, is the same as the apex of your pellet/slug flight. This is the most common zero method of many Field Target competitors in most classes. This allows for someone in Hunter class to have a zero point (usually somewhere between 30 and 35 yards). This allows for all shots that do not hit zero, to use holdover, because the zero is at the highest point of the projectiles travel, all other shots, nearer, and farther from zero, will be lower. WFTF competitors use this method as well, but they generally do not use holdover, they click their elevation turrets. This means, that all shots nearer and farther from their zero will be lower. This allows them to be able to return to their zero, and turn the turret up to move the impact up. This is to eliminate confusion of possibly not returning to zero.

You can find your apex by doing this:

Put out targets from 30 yards out, in 5 yard increments. Zero at 30. Then shoot at 35. If the pellet/slug goes higher, rezero at 35. Shoot at 40. If its still high, rezero again. Keep doing this until you see the pellet/slug stays the same at the next distance, or is a little lower, either one. Now you are zeroed at your apex, and ALL shots, closer, as well as farther will impact lower than your crosshairs..

Tom Holland 

Field Target Tech 
 
Upvote 0
Have you used an app like Chairgun or Strelok? If you can input the required parameters, eg fps, BC, weight and scope height you can see the curve your slug will take. What you have said is not what I normally see, but a high scope mount height could give your results. As I'm sure you know the barrel is pointed up relative to the scope, and the higher up the scope the further out the far zero will be (relative to the near zero)
 
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We don't have enough information to know for sure but the 1st zero being at 25 yards didn't seem likely when I first looked at it. FX's claimed BC for the .25 hybrids is 0.09. With a fairly high scope mount 2.0" above the bore and a 25 yard first zero at 900fps MV, the 2nd zero is at 35 yards and the trajectory is down almost an inch at 50 yards. For it to have a 2nd zero beyond 50 yards, the muzzle velocity would have to be 1100fps or the scope towering 2.9" above the bore, or some combination thereof.
 
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Hi

IMG_20200904_083546.1599201638.jpg
Regards

Enkey 
 
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I started experiencing this myself when I started shooting FX guns. All my guns before had 2.5" or less of scope to bore, but my FX guns are 2.8 and 3 inches over bore, which makes sighting it at 25 yards a bit more of a challenge. 

For a flatter PBR, I sight in at 40, and then my projectile never goes over POI, only under, so no hold unders are necessary.
 
Upvote 0
M,

I don't have any experience with that particular gun, but what you described is very common with many guns and combinations. 

When one sights in at an indiscriminate distance, 25 yards as in your example, one of 2 things will happen. You will have a zero at 25 yards. As you described, at 50, the impact is higher than your 25. This means, at a point further than 50, let's say 75 for arguments sake, the impact will be the same as 25. This is totally normal for a zero that one wants at an indiscriminate distance. 

The second thing that COULD happen, is the distance of your zero, is the same as the apex of your pellet/slug flight. This is the most common zero method of many Field Target competitors in most classes. This allows for someone in Hunter class to have a zero point (usually somewhere between 30 and 35 yards). This allows for all shots that do not hit zero, to use holdover, because the zero is at the highest point of the projectiles travel, all other shots, nearer, and farther from zero, will be lower. WFTF competitors use this method as well, but they generally do not use holdover, they click their elevation turrets. This means, that all shots nearer and farther from their zero will be lower. This allows them to be able to return to their zero, and turn the turret up to move the impact up. This is to eliminate confusion of possibly not returning to zero.

You can find your apex by doing this:

Put out targets from 30 yards out, in 5 yard increments. Zero at 30. Then shoot at 35. If the pellet/slug goes higher, rezero at 35. Shoot at 40. If its still high, rezero again. Keep doing this until you see the pellet/slug stays the same at the next distance, or is a little lower, either one. Now you are zeroed at your apex, and ALL shots, closer, as well as farther will impact lower than your crosshairs..

Tom Holland 

Field Target Tech
Click to expand...

Exactly. Well stated.


 
Upvote 0
We don't have enough information to know for sure but the 1st zero being at 25 yards didn't seem likely when I first looked at it. FX's claimed BC for the .25 hybrids is 0.09. With a fairly high scope mount 2.0" above the bore and a 25 yard first zero at 900fps MV, the 2nd zero is at 35 yards and the trajectory is down almost an inch at 50 yards. For it to have a 2nd zero beyond 50 yards, the muzzle velocity would have to be 1100fps or the scope towering 2.9" above the bore, or some combination thereof.
Click to expand...

I started experiencing this myself when I started shooting FX guns. All my guns before had 2.5" or less of scope to bore, but my FX guns are 2.8 and 3 inches over bore, which makes sighting it at 25 yards a bit more of a challenge. 

For a flatter PBR, I sight in at 40, and then my projectile never goes over POI, only under, so no hold unders are necessary.
Click to expand...

There you go.
 
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Prior to having the Power Plenum, my zero at 20yds was spot on at 50yds as well. The zero remained flat to 25yds, but all other distances out to 50 needed adjusting down. The distance below 20yds needed to be adjusted up. That is, 15yds and 10yds. This is due to the pellet trajectory as explained previously.

Now, with the Plenum installed, I re zeroed because my POI had shifted. Thus, I indexed the liner "Impact X 700, .25 to shoot closest to the target at highest point. After adjusting the Zero at 20yds, all my prior settings remained the same except the 50yds. This poi was a little higher, 4 clicks down brought it spot on target. So, now I have to check what will be my new distance where it will be spot on again. Maybe, 60 to 75yds. I shoot JSB's MK11's 33.95gr. Stay safe all.
 
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