Question about sling tension affecting AR accuracy

[Ironbar]

This is a question that's been burning in my brain since I bought my upper a couple days ago. The prevailing opinion on virtually every forum discussing AR rifles is that free float barrels are the way to go to achieve maximum accuracy. Sling tension on a standard AR front sight will most certainly affect point of impact to such a degree that reports have been made of being several inches off center.

HOWEVER, everything I've seen so far appears to be mere parroting of things everyone else has already said, and not based on actual field testing. It's like it's become common knowledge without anyone ever having proved it.

Does anyone have any facts to back this up? I mean, I'm a strong guy and I like my sling fairly snug when I'm in position, but in reality am I causing so much tension on the barrel that I'm warping the thing? It doesn't seem possible that I could bend it so much that I'm throwing my rounds that far off my point of aim.

What say you?   

[eaglescouter]

I say go prone and shoot a group without a sling, then shoot one with a very taught sling. 
Measure the difference in groups, center to center and report back with your facts.

[hogfamily]

In my personal experience, and in observing others, I believe it depends on the rifle and how stout the barrel is.

My personal experience with S&W 15/22s is that I am positive that if I put  too much tension on the sling it distorts the barrel and causes inconsistent groups.  I have seen this happen with other shooters including my two older boys.

With my AR15 I can't put on enough sling pressure to change the groups.

I have seen similar results with other shooters.

Maybe with a little range time you could determine at what point, if any, is sling pressure is causing barrel distortion and inconsistent groups?

[Birdman]

Without doubt, with a tight sling, my AR will drop 1/2" or more at 27 meters. It is a RRA Entry/Tactical. I added a quick-release sling swivel to the front of the quad rail, problem solved.

[Maximum Ordinate]

Ironbar,

My comments are applicable to Appleseed shooting, including the KD AQT. 

The short answer is yes, a shooter can put enough tension on a sling that he gets a significant shift (to Appleseed standards) between POA and POI.  In that situation, something is not right.

In Appleseed, we're not snipers or benchrest shooters craving sub-MOA performance.  We're Riflemen - field shooters.  Our goal is to consistently hit a man-sized target out to the Rifleman's Quarter Mile.  If you and your USGI sling are deflecting the barrel so much it's taking you off target, either it's way too tight or there's a problem mating the barrel to receiver.  While free-floated uppers are nice, they aren't needed to excel at the Known Distance AQT (400 yards).

Think of you and your rifle as a single integrated "system".  Your goal is to get that system operating with consistency and repeatability.  As you shoot more using a sling, you'll develop a feel for your sweet spot in sling tension.  You won't need to mark the sling - you'll just feel what's right for you.  As you learn to do the same thing, the same way, every time - you'll get the same results.  That's consistency and repeatability.  Might you have a tiny amount of deflection in your barrel?  Perhaps, but your system as taken that into account.

You can spend time analyzing the differences in zero between shooting sling-supported or off a rest.  What will you do with that data?  It won't change what right feels like when wearing your sling.  It won't affect the muscle memory you develop to be consistent and repeatable.

All this said... there will likely be a change in zero when moving from sling-supported position to a rest or bench.  Why?  It's probably not the barrel deflection, but that the system of rifle & shooter has changed significantly.

Good luck,
Rusty

[maxwell]

I was having problems with sling tension affecting accuracy on my Palmetto AR upper (16" M4 (lightweight?) profile barrel), and some deflection was actually visible. When I drank the Kool-Aid and put a free-float rail on it, I then discovered that Palmetto hadn't properly torqued the barrel nut, and it was little more than finger tight . I'm not sure which was the bigger issue, but it does happen.

[Agrivere]

Will sling tension affect point of impact on an AR? If your sling is attached in the standard spot under the front sight, absolutely. When I hang my Magnetospeed on the barrel it changes the point of impact. Anything that affects the way that barrel vibrates will affect the point of impact. Remember you don't actually need so much force as to deflect the barrel; it only takes a few ounces of force to change the harmonics and change the point of impact as well as the size and shape of your groups.

The question isn't whether or not it will affect your shots, it's whether or not it will affect your shots enough to matter. In my opinion it will, but it does depend on how well you can shoot as to whether or not you'll see it or care. You asked for personal real world info, so I'll share mine. Last year I went to an Appleseed with a non-floated 22 upper on a standard AR lower.  My position is pretty consistent in prone, and I can generally shoot groups around 1 MOA in prone with a good rifle and good ammo. Using the non-floated upper in prone my groups would move about 1 MOA every time I slung up. Different directions each time, but it was definitely there and definitely noticeable.  In sitting of course you have a somewhat different sling angle and different sling tension. Groups for me moved about 2 minutes. Standing I don't use the sling, and when taking all the tension off the barrel groups moved up about 10 minutes. Yikes!

The next day i switched to another upper with a floated barrel and all of a sudden my zeros quit wandering and my groups went back to normal. No change in zeros when changing positions.

So back to the question of "does it matter"? You'll have to decide that for yourself. If you're generally shooting 4-5 minute groups in prone you may not notice it, and it likely won't matter. For me, it drives me nuts if the bullets don't go where I pointed the rifle, and I would not dream of having an upper without a floated barrel. Can you shoot a rifleman score with a non-floated barrel? Absolutely. It's been done thousands of times.

When you consider that you can buy an AR float tube on eBay for like $50, to me it's a no brainer. And while I generally agree with Rusty's "system" analogy, when you can dramatically improve your system with a small investment of time and money that seems like an easy choice. And as I've said many times, the more accurate your "system" the faster you will learn, as you'll know those off call shots were you and not your rifle.