Change in POI from bench to offhand

[Aero Denezol]

..Offhand is hitting about 8-12" lower than the bench at 100 yards. What is the solution for this? Taller mount?

The scope is an ACOG with the factory TA51 mount. The mount is on tight.

I apologize for my ignorance, I usually shoot iron sights and don't have significant experience shooting magnified optics. The only other magnified optic I have on a sporter is a Vietnam era Colt carry-handle scope (4x) which shoots the same POI whether standing or seated.

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[Koda]

something is loose or its your technique. Your group size would be larger but your POI should not change.

 

[Xaevian]

If on a bench, you are resting the barrel on a bag, that will change the POI like that. That would be my 1st thought.

 

[po18guy]

+1 Take note of where the barrel/fore end pressure is off the bench. Then try supporting the barrel at the same point off-hand. Conversely, from the bench, you can place the front bag in the same position as your off-hand is on the forearm.

 

[American123]

If something isn't loose, your barrel harmonics are being significantly effected by however you are using the bench.

 

[P7M13]

Cheek position, parallax, eye box.
The first always needs to be the same, makes a difference in parallax, and if your eye position is different (as it will be), that also affects POA/POI.
I may be using parallax incorrectly, but I'm specifically talking about the optical image centered in the scope, with the black outer ring being the same width as when you are on the bench and completely concentric.
Also, 8-12" lower may be an anticipatory compensation to the recoil. I'll do dud drills with non-firing rounds to test whether or not I am anticipating.

 

[Aero Denezol]

+1 Take note of where the barrel/fore end pressure is off the bench. Then try supporting the barrel at the same point off-hand. Conversely, from the bench, you can place the front bag in the same position as your off-hand is on the forearm.

That could be it. In the offhand my support hand holds close to the magwell but when I benched the gun it was supported closer to the muzzle, because the stupid VFG was in the way. I'm going to remove that thing and re-zero.

Cheek position, parallax, eye box.
The first always needs to be the same, makes a difference in parallax, and if your eye position is different (as it will be), that also affects POA/POI.
I may be using parallax incorrectly, but I'm specifically talking about the optical image centered in the scope, with the black outer ring being the same width as when you are on the bench and completely concentric.

If that's the case this is disappointing. I though Trijicon ACOG were supposed to have little or no parallax inside 100 yards.

I built a CAR15 clone with a Colt 4x scope and that one shoots the same every which way. So I was baffled why the ACOG was shooting low. But it makes sense it could be the way I zeroed vs. the way I was holding offhand.. Thank you all for your help.

 

[jjfitch]

It would be nice to mention the cartridge and rifle!

Most likely you are pushing against recoil which results in driving the muzzle downward causing lower POI!

When shooting from a supported bench position the support limits the downward movement!

 

[jjfitch]

It would be nice to mention the cartridge and rifle!

Most likely you are pushing against recoil which results in driving the muzzle downward causing lower POI!

When shooting from a supported bench position the support limits the downward movement!

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[Aero Denezol]

SOLVED: I re-zeroed by supporting the barrel in the same place my support hand holds the fore-end in the offhand position. Now POI from the bench = POI offhand. Thank you gentlemen for pointing this out. I've never had this happen before. Lesson learned.

Thank you @P7M13 for pointing out the parallax issue. I'm not sure why I thought ACOGs were parallax free. It turns out they are highly parallax sensitive. I've heard of people using the shadow of the front post to "index" the reticle and get a consistent cheek weld. Otherwise groups can move around quite a bit.

I've spent almost my entire shooting career with iron sights, which I am good at. This has been an adjustment but I am determined to learn how to use it.

 

[bbbass]

That could be it. In the offhand my support hand holds close to the magwell but when I benched the gun it was supported closer to the muzzle, because the stupid VFG was in the way. I'm going to remove that thing and re-zero.

SOLVED: I re-zeroed by supporting the barrel in the same place my support hand holds the fore-end in the offhand position. Now POI from the bench = POI offhand. Thank you gentlemen for pointing this out. I've never had this happen before. Lesson learned.

Yep, I learned the hard way not to support the rifle by the barrel on a bench rest. The barrel will jump up and will be falsely zero'd in for that amount of jump. As we now know, all rifles are intended to be supported by either the forestock or the handguard.

 

[Xaevian]

If they aren't free floating barrels, resting the handguard differently than where you hold it can do the same thing, as those guards typically have a pressure point at the end, as Aero found.

 

[308]

SOLVED: I re-zeroed by supporting the barrel in the same place my support hand holds the fore-end in the offhand position. Now POI from the bench = POI offhand. Thank you gentlemen for pointing this out. I've never had this happen before. Lesson learned.

Thank you @P7M13 for pointing out the parallax issue. I'm not sure why I thought ACOGs were parallax free. It turns out they are highly parallax sensitive. I've heard of people using the shadow of the front post to "index" the reticle and get a consistent cheek weld. Otherwise groups can move around quite a bit.

I've spent almost my entire shooting career with iron sights, which I am good at. This has been an adjustment but I am determined to learn how to use it.

uR pretty good if your bench POI is the same as your offhand POI. I'd encourage you to get involved in a NRA Highpower Match out at DRRC.

 

[Aero Denezol]

uR pretty good if your bench POI is the same as your offhand POI. I'd encourage you to get involved in a NRA Highpower Match out at DRRC.

Very kind, thank you. I notice not many people shoot offhand. I find this type of shooting very rewarding.

I had a goal to do a Highpower Match before family and work got in the way of my Saturdays. It's still something I want to do one day, time permitting.

 

[Aero Denezol]

If they aren't free floating barrels, resting the handguard differently than where you hold it can do the same thing, as those guards typically have a pressure point at the end, as Aero found.

That's what I did, I rested on the front part of the handguard and the up pressure gave me a different zero. It is a KAC RAS, definitely not free-floated.

 

[Xaevian]

That's what I did, I rested on the front part of the handguard and the up pressure gave me a different zero. It is a KAC RAS, definitely not free-floated.

I found this out myself through a bad experience that could have turned out much worse.

I have only 1 non free floating hunting rifle, a Savage M99 in .308. A deer presented itself broadsided about 300 yards away in a 30 mile crosswind. I decided to use my pack and take a resting shot as I was too cocky to walk closer for an offhand shot. Now this rifle is about 1.5 MOA normally, typical for a vintage hunting rifle. (It was made in 1957).

My vitals shot turned into a headshot. I was like, WTF? It was a 1 shot kill, but luck made it so. I was not happy, but this was the reason as I found out later. Would've been different with any other rifle of mine, as I have no problems hitting an 6 inch plate at that distance with them.

Wotan guided my bullet that day and made sure the animal didn't suffer and I learned a valuable piece of knowledge.

So, I wanted to pass that along to others.

 

[308]

Very kind, thank you. I notice not many people shoot offhand. I find this type of shooting very rewarding.

I had a goal to do a Highpower Match before family and work got in the way of my Saturdays. It's still something I want to do one day, time permitting.

My daughter and I went through the CMP course at DRRC and I found out how hard offhand is and truly appreciate those who can steady and time their shots. Even though we were taught how to properly sling up the Garand and AR, I still sucked…lol

 

[powermad]

Offhand rifle shooting and a red dot on a pistol is pretty much the same.
You'll never hold it still, trying to is effort
and concentration wasted that can be used elsewhere.
Hats off to those good at it, I need a lot more practice.

 

[41mag]

I learned of forearm pressure some time back using my first breakdown carbine.