Is it normal for POI to shift?

[pepperbelly]

I zeroed my DPMS LR308 SASS on the bench at 100 yards then confirmed it at 200 yards. Then I went to a prone position and saw that I was hitting low.
Is it normal for the POI to be different between the bench and prone positions?

 

[Topstrap]

Re: Is it normal for POI to shift?

You should strive to not have it do that. Just minor positioning changes you're not noticing. Might just be you're putting more forward tension on the bipod prone or shoulder or cheek touching a tad different.

I'm basing it on it not changing for us when we shoot from a table or prone or thru some tree limbs. Try to make everything the same and it should correct that for you.

Topstrap

 

[pepperbelly]

Re: Is it normal for POI to shift?


Thanks. One thing I did notice is that my bipod seems short when prone. It's a Harris 6-9 BR-S. It's fine from the bench but I think I would like a slightly taller bipod when prone. On the bench I had it collapsed all the way and when prone I had it extended all the way.

 

[bschneiderheinze]

Re: Is it normal for POI to shift?

My rifle hits about 3/4" low because are range has concrete benches and it is near impossible to set or put tension on the bipod. I shoot at the range for load devlopment and then sight in the rifle in the prone position for long range work.

 

[veganshooter]

Re: Is it normal for POI to shift?

Your shoulder placement and tension often change when going from bench to prone. This can affect pressure on the bipod.

 

[pepperbelly]

Re: Is it normal for POI to shift?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rubicon1996</div><div class="ubbcode-body">My rifle hits about 3/4" low because are range has concrete benches and it is near impossible to set or put tension on the bipod. I shoot at the range for load devlopment and then sight in the rifle in the prone position for long range work. </div></div>

My range also has concrete benches. When I shot on the bench I used one of the carpet samples we have under the bipod feet, and the bipod was collapsed all the way.
When I shot prone I was laying on a 4'x8' pad we have at the range and the bipod was fully extended.
I think I do remember loading the bipod a little more while prone. I was also trying to position myself more directly nehind the rifle while prone.

 

[sled_mack]

Re: Is it normal for POI to shift?

Lowlight has a video on here showing how to shoot from a bench in such a way that you won't see the shift in POI. The difference is how you position your body behind the gun.

 

[Graham]

Re: Is it normal for POI to shift?

Is the POI shift normal? Yes, somewhat. Is is due to pressure on the bi-pod? No. Is it due to your position behind the gun? In general, yes.

 

[Sterling Shooter]

Re: Is it normal for POI to shift?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pepperbelly</div><div class="ubbcode-body">
I zeroed my DPMS LR308 SASS on the bench at 100 yards then confirmed it at 200 yards. Then I went to a prone position and saw that I was hitting low.
Is it normal for the POI to be different between the bench and prone positions?</div></div>

When recoil resistance is not consistent then POI can be expected to be inconsistent, even for a string of fire fired from a particular position where the positon is rebuilt for each shot; and thus, a bigger rather than smaller grouping. When the 5 factors of a steady position are applied consistently, a shooter can shoot from bench to prone and expect very little divergence in point of impact (for me, it's under a minute) when the rifle can be controlled with similar pressure. Some times similar pressure will not be possible and sight adjustment may be useful.

 

[Graham]

Re: Is it normal for POI to shift?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sterling Shooter</div><div class="ubbcode-body">When the 5 factors of a steady position are applied consistently, a shooter can shoot from bench to prone and expect very little divergence in point of impact (for me, it's under a minute) when the rifle can be controlled with similar pressure. Some times similar pressure will not be possible and sight adjustment may be useful. </div></div>With optics, POI shift between bench and prone is not always about pressure on the rifle.

You are saying that when a proper shooting position is applied consistently and correctly there is little shift in POI between shots. That does not make sense. Assuming that everything is consistent and correct, then theoretically there should be no POI shift at all. But you admit that even when you shoot properly you experience a POI shift between bench and prone. The question is: Why? Are you saying that its only because similar pressure on the rifle is not possible? If so, then what do you mean when you say 'similar pressure'? Where and How?

 

[Bill Larson]

Re: Is it normal for POI to shift?

paralax................????

 

[Sterling Shooter]

Re: Is it normal for POI to shift?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sterling Shooter</div><div class="ubbcode-body">When the 5 factors of a steady position are applied consistently, a shooter can shoot from bench to prone and expect very little divergence in point of impact (for me, it's under a minute) when the rifle can be controlled with similar pressure. Some times similar pressure will not be possible and sight adjustment may be useful. </div></div>With optics, POI shift between bench and prone is not always about pressure on the rifle.

You are saying that when a proper shooting position is applied consistently and correctly there is little shift in POI between shots. That does not make sense. Assuming that everything is consistent and correct, then theoretically there should be no POI shift at all. But you admit that even when you shoot properly you experience a POI shift between bench and prone. The question is: Why? Are you saying that its only because similar pressure on the rifle is not possible? If so, then what do you mean when you say 'similar pressure'? Where and How?</div></div>

No divergence between POA and POI is essentially theoretical realization of the zeroing task. For this to come about everything regarding the shooter's relationship between the gun and the ground must be extraordinarily consistent, as well as require extraordinary match grade equipment. Similar pressure/control over the rifle is as close as it gets when going from one position to another, since the contact between the shooter, gun, and ground will be physically different for each position. With similar control rather than identical control from position to position, the change in recoil resistance will force the bullet to go someplace other than where exactly aimed while in what ever position for initial zeroing. It's not a big deal; and, only in some competitions would countering for dissimilar pressure through zero refinement be useful, such as in HP competition.

In addition to the matter of recoil resistance there's the matter of perspective of aim, which can also cause POI change when going from one position to another or even the same position if it is not rebuilt as when the rifle was initially zeroed.

 

[Lowlight]

Re: Is it normal for POI to shift?

Part is body position, most put the shoulders either in line with the hips, or behind the hips when shooting from a bench. This changes a few things, recoil characteristics, because you are no longer managing the recoil the same. Also your cheek weld changes, you've rotated your head and altered your cheek weld.

The fix, lean forward on the bench and bring your shoulders in front of your hips. This will also bring your cheek weld closer to the same, like prone.

You also can shorten your stock, as you move from prone to other positions, the shorter stock will maintain your cheek weld better.

 

[pepperbelly]

Re: Is it normal for POI to shift?

MY SASS has a Magpul ACS stock so I can adjust it. I plan on shooting very little at the bench and am working on my prone shooting. I was really just curious if the shift in POI is normal. If it is then I can be prepared for it. I will switch more often to see if the shift continues or if I was doing something specific to cause it.