Free-floated or Not, It Doesn't Matter

Forums General Discussion Free-floated or Not, It Doesn't Matter

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    spinj
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    Free-floated or Not, It Doesn’t Matter

    The debate on whether a fixed or free-floating barrel system rages on.  Like many of you, I have questioned both designs, particularly on whether either type is more able to hold zero over the other.  In my opinion, a good way to acknowledge which design is superior is to understand the nature of metal and how it behaves under certain circumstances.  In this brief write-up, I’ll share at least two causes of point-of-impact (POI) shift and them being a by-product of both designs.  Such causes are temperature change and unwanted pressure.  
     
    First off, I believe that a free-floating construction lends itself particularly well to powder-burners mainly because it is much more able to offset the extreme forces firearms are subjected to during a shot cycle.   Unlike with air rifles, the barrel on firearms is exposed to harsh cycles of vibration, high pressures, and heat.  As we all know too well, metal expands when it is heated.  It is heat that is one of the great detractors of accuracy.  On air rifles heat is not naturally occurring during a shot cycle.  Therefore, POI shift, regardless of how a barrel is mounted on an air rifle, is almost a benign phenomenon or even a problem that the air rifle user shouldn’t have to worry about.  The shift is usually the result of some other problem, like for example, a faulty regulator or worn out O-ring seal.    
     
    The way I view it, a barrel can be unconventionally thicker, but it still is going to contract and/or expand in certain temperatures.  That’s just the inherent characteristic of metal.  Leave an eight-inch steel rod outside in the desert summer heat for a good couple of hours and it will bend due to the extreme temperature playing its role in altering the steel’s molecular structure.  The longer the rod the more dramatic the bend is going to be seen from a given vantage point.  It is almost impossible to detect with the naked eye, but I’m sure that with the proper instruments to check for it you would see that the rod succumbs to the heat.  So, a steel barrel, just by itself, will be influenced by temperature and thereby change the POI of the projectile, free-floated or not.
     
    But what if an air rifle is used in an environment with a stable temperature?  In attempting to answer this question, I set out to find out on my own.  I must state, though, that I first needed to accept the fact that there was no way that I was going to be able to see if something else like harmonics or vibration would change POI simply because I didn’t have expensive, high-speed cameras capable of recording in ultra-slow motion to detect them.  Albeit, I had the conception that it may not be harmonics at all but rather the change in barrel position influenced by unwanted pressure.  With that (and because I’m the kind of person who would much rather see with my own eyes the effects as they are being manifested and not just accepting results from post-test numbers-driven data), I decided that the method I was going to use to verify this would involve the use of a barrel-mounted laser.  I used my Air Arms S410 Xtra to perform the test.  With the laser I thought that I would be able to detect any dot deviation (from its superimposition) from the crosshairs of my scope.  I figured this would be one good way to prove that the POI shift was a premier result of, perhaps, something as simple as the torque setting of a stock screw.  As it turned out, and just as I hypothesized, this was indeed the result.  The slightly over-torqued stock screw on my S410 led a section of the inletting side on the stock to push the air tube up, and since the barrel (or shroud, rather) is reinforced by a barrel band its position was therefore changed.  I suspect that POI change is likely with regard to this kind of situation with either a free-floated or braced barrel.  

    Post entry: Notwithstanding the explanation above, there could also be the supposition that can be made as a result of the POI change, and that is, instead of movement caused by the pressure, the change in barrel position may have been caused by movement of the barrel at the connection juncture –the point at which the barrel and breech are attached—and not because of the barrel actually bending.
     
    Some shooters declare that using a different stock changes the gun’s impact point of the projectile by changing its harmonics or vibration pattern.  This could be one possibility, but I personally would not hastily conclude that it is a definitive cause just because the shift has been confirmed by a shot group.  In order to rule out coincidence as one factor, I believe it is imperative that testing through the use of methods that yield more concrete and observable examples (to the eyes) should be done.  I mentioned it in the beginning, I like to make sure that I see proof with my own eyes instead, and in the test the laser did not lie to me.     
     
    In my opinion, and from my experience, a good way to mitigate the problem of a POI change even though a barrel is free-floated or reinforced by a barrel band is by clamping the scope mounts as close as possible to the muzzle; however, this is not a very practical solution.  (Thus, it goes without saying, enter the bullpup air rifles.)  Not to elaborate a whole lot on it in an attempt to keep within the focus of this article, a bullpup configuration helps to an extent in this regard.  One reason why bullpup air rifles like the Cricket, Vulcan, and Mutant are so accurate is because their scope mounts are anchored midpoint of the barrel.  Think of the barrel as a lever.  If you were to exert upward pressure on one end of it while the other end is held, you may see a slight bend upwards somewhere in between each end.  Now, if you were to apply the same amount of pressure about five inches from the muzzle while the other end is still being held, you most likely won’t see any bend at all because the area becomes stiffer as the distance between them is lessened.  This is why I said in the beginning of this paragraph that this is an effective way to prevent any barrel-related POI issues.    
     
    I understand that others will have their disagreements.  However, I’ll conclude this article by stating that it is not so much that a free-floating barrel is better than one that relies on a barrel band, and vice versa.  Hopefully, I’ve shed some light on barrel integrity by placing on the bench (no pun intended) what I’ve discussed here.  Nevertheless, I think one of the things to keep in mind on maintaining zero is that your air rifle’s barrel isn’t being gorilla-handled and that it is undisturbed and free to do what it wants to do, again—for emphasis—free-floated or not.  
     
    Shoot safe … and straight, everyone!

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    Michael
    Keymaster
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    Thanks for taking the time. Some interesting points. 

    I’m no engineer, but I’ve heard that the force required to bend a barrel is very high. So if you’re just referring to temperature then I would think the temperature would have to be very extreme for a very long time.

    In a traditional rifle the weakest point would then be the connection points to the breach. Perhaps this is why tuners like AZ permanently “steel-bed” the barrel to the breech?

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    Dan25
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    I am a believer in free floating a bbl. for accuracy in conventional rifles.  Not so much in air guns.  In comparing powder burners vrs. air guns something to be taken into account is bbl attachment on air guns is feeble at best in comparison to center fire rifles.  They are also much thinner than powder burners.  This can allow minor pressure to cause point of aim movement and in the case of my Marauder a change in zero.  Accordingly, I like a bbl band out near the end of the cylinder to help stabilize air gun bbls.

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    spinj
    Participant
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    Thanks for your thoughts, Michael.  I agree with you that the juncture at which the barrel and breech are connected can also be responsible for point-of-impact issues.  Perhaps this may have been the actual cause of the laser dot moving from its original position.  Also, regarding your statement that it would take an extreme amount of force to bend a barrel, I agree with it as well, however, to an extent that pressure (which may lead to torquing of the barrel) is constant.  I have seen that even the steel of decent barrels do bend ever so slightly and just enough to affect POI a significant amount, especially at far distances.

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