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To Flute Or Not To Flute?

Few things are as controversial as barrel fluting.  There are both facts and theories that give good reason why to flute and why not to flute your barrel.  The first thing is to dismiss some of the misconceptions of what fluting can accomplish.  It is widely thought that fluting a barrel will make it stiffer.  This is not true.  Now your thinking that if fluting my barrel will not make it stiffer and more accurate than why in the world would I want to flute my barrel?  The answer would be to make your barrel lighter.  So if I want to build a very light rifle I should have the barrel fluted? 

No, in fact you cannot build a very light rifle with a fluted barrel.  In order for a barrel to be safe you must have a certain amount of material completely around the bore.  We will call that “The Minimum Safe Thickness”.  If a barrel is at this minimum, fluting it would reduce that dimension beyond the minimum and destroy it’s integrity.  The barrel would bulge or even burst.  Since a barrel can only be as strong as its weakest part than the bottom of the flute cannot be closer to the bore than the minimum safe thickness, which is the same as a round barrel with no flutes.  This makes the round barrel lighter.

What makes a barrel stiff?

When something flexes whether it is a barrel or a piece of paper there are 2 opposing sides.  One side gets longer and the other side gets shorter.  More exact terminology would be that one side is under tension and the opposing side is under compression.  When a barrel flexes it forms an arc.  The closer the two sides are together or the smaller the diameter of a barrel, the easier it will flex.  The outside of the arc only needs to get a little bit longer, the inside arc only needs to get a little bit shorter and you have a whole degree of deflection.  There is way more to it than just opposing sides.  There are all the points between the two sides.  As a barrel flexes there are compromises between all of these components.  I’m using an over simplification to illustrate a point.

 

On a thicker barrels in order to get the same amount of deflection the outside arc must get much longer and the inside arc much shorter.  So in essence to get the same amount of angular defection on a larger Diameter barrel as you get on a small diameter barrel it takes significantly more force. 

 

So why would I want to flute my barrel?  Answer: To meet weight requirements.  Instead of comparing the stiffness between say a fluted #7 barrel and a Unfluted #7 you need to compare a fluted 5 pound 26” barrel to a Unfluted 5 pound 26” barrel.  The fluted barrel will have a larger diameter and will be stiffer.  There are those that say, “fluting a barrel induces stress in the barrel metal and causes accuracy problems” this can very well be true.  Like most things, it seems like there is an easy way and a right way.  Setting up a barrel in the mill for fluting is a very exacting, very time consuming task.  Then there is the actual cutting.  The tool must be very sharp.  Cuts need to be small and go-slow.  The convex cutters designed to be used on a horizontal mill set up have a very large cutting surface that creates a lot of heat and friction that will dull a cutter in a hurry. Dull cutters will bend metal out of their way.  A burr running along side the edge of a flute is the metal that was bent out of the way.  Stress has just been introduced into the metallurgy of the barrel.  It takes lots of small cuts and all day to flute a barrel.  If the time wasn’t taken to do it right then you are better off not fluting at all.  If the price seems too good to be true then it probably is.  Personally I have and use guns with both fluted and unfluted barrels.  If weight is not an issue, do not have your barrel fluted.  Fluting a #7 barrel with eight 3/16" wide flutes will reduce its weight by 14 to 16 ounces.  I personally prefer my varmint rifle to weigh 12 pounds instead of 13 it makes it easier to heft around.

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