Different POI with sling vs benched?

[Demos]

Hi guys,
I was out at the range sighting in my CMP M44 at 100 yards. Of a front rest and bags, I had it good and sighted in, getting consecutive "head shots" on a 25% silhouette. When I decided to practice shooting prone with a sling, I was shooting 4-5 inches low. Is it that I'm rusty shooting prone, or that slinging up tight on the front swivel, which is attached to the front barrel band, is shifting my POI? If its the latter, any advice for fixing the problem?

Thanks,
Demos

 

[wally]

You've rediscovered why barrels are "free-floated" for "match" accuracy.

 

[sixgunner455]

It's a different zero for position shooting vs. bench shooting precisely because of that phenomenon.

If it's a predictable shift, then you can just adjust for whichever way you're going to be shooting. Or shoot a group, adjust, and then do your shooting.

 

[chrome_austex]

Its definitely a POI change between positions. Bipod vs sandbag, sling vs held, even prone vs sitting. Even with NPOA, the gun will recoil differently when it's held differently.

I'd be pulling hard left in sitting position, and the bullet impacts would reflect it. Unfortunate perhaps, but true. One time I did a prone string forgetting my usual shooting glove, and it really threw my POI.

With practice and awareness you can make it a predictable POI shift.

 

[Slamfire]

I see it even in my Anschutz small bore rifle.

Sight it in on the bench, the POI changes when I shoot it prone with a sling.

It must be due to the different recoil dynamics and different position.

 

[Art Eatman]

The cause is from having a different pressure of the forearm on the barrel. If the barrel is free-floated, it shouldn't happen. If it continues, however, it's something in the style of control by the shooter.

I have low-pressure shims between the barrels and the forearm tips of my two pet rifles. On the benchrest, I always put the front sandbag in the same location as I put my hand when in the field. That way, there is consistency in the pressure between barrel and stock.

If a bipod is mounted in the same place as where the front sandbag is placed when at the benchrest, I would expect that there would be consistent pressure.

 

[plouffedaddy]

Art is correct. The harmonics of the barrel change when pressure is applied. Generally it will change in a consistent manner though and as long as you're aware of it it's workable.

 

[BCRider]

Even if the barrel is free floated in all cases it could still be a simple case of recoil dynamics, the mass of the rifle and how it is held.

If when benched there's often nothing to slow down the rise of the gun during recoil. Then when you use a prone position with sling the sling joins your hand and forearm to the fore end of the gun. So now the recoil has to lift more weight so it's not going to go as high or as fast. So the bullet tends to strike lower. It would be the same even if you shoot from the bench using a bag or bipod if you used your support hand to grasp the fore end up by the bag/bipod firmly so the mass of your hand was effectively added to the weight of the rifle.

By the same token where the butt pad rests against your shoulder and where on the butt pad you make contact will change how the recoil pivots up the gun when the round is touched off.

 

[Demos]

If I were to install a new swivel stud and swivel, that didn't interact with the barrel, would the change be less than the factory one?

 

[Cesiumsponge]

Also, folks tend to be less aggressive on the rifle when benched versus prone. They're not nearly as forward on it and that can lead to POI/POA shifts too

 

[henschman]

Yes, it would definitely help to have a front swivel that isn't attached to the barrel, but pressure on the barrel isn't the only thing at play. As others have said, the recoil impulse is different between the two techniques, and that has a big impact on POI shift too.