POI/POA Discrepencies with New Rifle

TheotherMikeG · Mar 10, 2019

I took out the new 556 MPR today to sight in. Sights are Magpul Pro irons. Set up at 25 meters. It took a lot of clicks to raise my POI to match POA, but I found that there was about a 3" difference in elevation shooting from a rest vs shooting from field positions. The photo below shows the results of 3 shots seated and 3 shots from the bench. POA was the center of the red circle for top photo, green circle for bottom photo.

I'm aware of my limitations as a shooter, but I do know how to use iron sights. The variation in elevation was consistent. Seated or prone always produced a shot or a group 3" lower.

Any wisdom for a wannabe rifleman?

Nature Boy · Mar 10, 2019

Are you resting the barrel or the forearm on the rest?

TheotherMikeG · Mar 10, 2019

Resting on the M-Lok rail

imashooter · Mar 10, 2019

TheotherMikeG said:
It took a lot of clicks to raise my POI to match POA

To raise it from what? So you screwed it in (down), right? What's the sight radius? They usually come close to 25 meters in the box. Just curious, where was your POI at the beginning when ranging at 25 meters? You can easily experience up to an inch or so difference between prone and a bench. Once you get through all this, it'd be best to do a final zero in the psn you anticipate to be your most common. It can make a difference in the end.

TheotherMikeG · Mar 10, 2019

Mechanical zero was approx 3.5" low and 2" to the right using the .60 width front post and large reticle. I lost track of the number of clicks down, but I expect it was in the 13-15 range. Sight radius is 20".

Skylerbone · Mar 11, 2019

And what was supporting the forend while at prone? If when shooting from a front rest at the bench the rifle is relaxed without pressure, then fired prone with say a preloaded bipod, you could be adding deflection to the rail and raising the front sight.

I can’t say this is the problem as we don’t yet have an answer on your set up.

Laphroaig · Mar 11, 2019

A possibility is that your head is on a different place on the stock and you are seeing the sights differently between the different positions. Make sure that you have a consistent cheek weld every shot. Many use the nose on the T-bar with AR's.

imashooter · Mar 11, 2019

TheotherMikeG said:
Mechanical zero was approx 3.5" low and 2" to the right using the .60 width front post and large reticle. I lost track of the number of clicks down, but I expect it was in the 13-15 range. Sight radius is 20".

Goodness. That should be an ezpz. Interesting. I would begin with checking "level" of the rail atop to rcvr and "level" of the rail atop the handguard. Separate "levels" but same/same as a single unit.

Is the top of the front sight post approx 2.5" - 2.6" above center of bore? That's what I have on a couple of F-marked and a non - F'd front sight posts. Zeroed at 50 meters though the difference will be insignificant even at 25 meters. You likely already saw this but just in case:

Scroll down to Adjustment.

https://www.magpul.com/products/mbus-pro-sight-front

https://www.magpul.com/products/mbus-pro-sight-rear

Chuck R. · Mar 11, 2019

Laphroaig said:
A possibility is that your head is on a different place on the stock and you are seeing the sights differently between the different positions. Make sure that you have a consistent cheek weld every shot. Many use the nose on the T-bar with AR's.

Agreed.

Consistent cheekweld through all positions?

Cause IF you're not looking through the irons the same way each and every time, you'll get a different POI. Kinda why guys like the "nose to charging handle" head position.

LoonWulf · Mar 11, 2019

Chuck R. said:
Agreed.

Consistent cheekweld through all positions?

Cause IF you're not looking through the irons the same way each and every time, you'll get a different POI. Kinda why guys like the "nose to charging handle" head position.

This is one of my issues with irons, ill end up shooting 6"+ in different direction one day to the next because my head placement isnt consistent with irons.

TheotherMikeG · Mar 11, 2019

Okay, the top of the sight post is approx 2.6" above center bore, perhaps a couple tenths more. I THINK my cheek weld is consistent, but I was shooting alone so no confirmation. My experience is with tech sights on a SKS and it shoots consistently where it's aimed. This is a new rifle though, so I could be all over the cheek piece.
I've never shot "nose to charging handle", nor have I seen it done. I'll have to look that up. Thanks to all for the responses.

Coal Dragger · Mar 11, 2019

Across the course shooters often find that they need different dope on the sights for different positions. I learned this back in 1998 shooting iron sights on a beat to hell M16A2 at Edson Range in USMC boot camp.

A 3” deviation at only 25 yards is pretty significant though, my suspicion is that your head position is creeping up on the stock a lot more in prone than from the bench, as well as your cheek position. So your angle on the sights is considerably different in prone.

As long as your groups are good from prone, I’d zero for prone, check sitting, kneeling, and standing and note the changes to POA/POI.

TheotherMikeG · Mar 11, 2019

Skylerbone said:
And what was supporting the forend while at prone? If when shooting from a front rest at the bench the rifle is relaxed without pressure, then fired prone with say a preloaded bipod, you could be adding deflection to the rail and raising the front sight.

Just my hand supporting the forend, no bipod.

Coal Dragger said:
A 3” deviation at only 25 yards is pretty significant though, my suspicion is that your head position is creeping up on the stock a lot more in prone than from the bench, as well as your cheek position. So your angle on the sights is considerably different in prone.

The more I think about it the more I believe that's true. Thank y'all for your help!

POI/POA Discrepencies with New Rifle

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