*A Service Rifle Master Armorer's perspective on fluting:*

We do not flute, nor recommend it, for Service Rifle and Match Rifle applications.

Here's some of the reasons why:

First, it reduces the strength of the barrel, so you pay more for less;

Second, the added weight of the Heavy Barrel is generally considered a good thing for service rifle/match rifle shooting;

Third, the added money spent on fluting is better spent on a better quality barrel, like a Krieger;

Fourth, the very process of fluting can disturb the bore's internal, and actually diminish the quality of the bore. Again, you pay more for less.

Fifth, The actual amount of weight savings is generally rather small in most gas guns, since many areas cannot be fluted.

However, if weight is a key criteria, fluting, properly done, can be a valuable process, and should be considered.

--Clint McKee

*A engineer's perspective on fluting:*

These discussions on fluting are guaranteed to produce lots of controversy!

All you really need to know is that as you take material off you reduce the stiffness.

So long as the material properties remain unchanged (specifically, the material strength), you CANNOT remove material from ANY shape, and make it stronger! A clever engineer, however, can *move* material to make the part stronger...

Anyhow, in a humble attempt to end this controversy for once and for all, I've decided to try a cold, hard, mathematical analysis of a typical real-world situation.

**Given:**

* Weight is directly proportional to cross-sectional area. (Specifically, the weight is equal to the cross-sectional are times the length, times the material density.)

* Rigidity (stiffness) is directly proportional to Area Moment of Inertia.

* Surface area is directly proportional to the outside perimeter. (Specifically, the surface area is equal to the perimeter times the length.)

Both "givens" are per every basic engineering Statics text.

**Test subject barrels:**

**Remington 700VS:**- outside diameter: 0.850"
- bore: .300 bore with six .308 grooves, 50% grooved
- flutes: none
- Cross-sectional area: 0.493 sq.in.
- Area Moment of Inertia: 0.02489
- Perimeter: 2.666"

**Remington 700VSF:**- outside diameter: 0.850"
- bore: .300 bore with six .308 grooves, 50% grooved
- flutes: six, 3/16" wide, 3/16" deep, full radius
- Cross-sectional area: 0.312 sq.in.
- Area Moment of Inertia: 0.01411
- Perimeter: 4.276"

**Hypothetical barrel for comparison:**- outside diameter: 0.7005"
- bore: .300 bore with six .308 grooves, 50% grooved
- flutes: none
- Cross-sectional area: 0.312 sq.in.
- Area Moment of Inertia: 0.01127
- Perimeter: 2.197"

**Comparisons:**

**0.850" Fluted vs. 0.850" Plain:**

- Cross-sectional area (weight): 36.7% less
- Area Moment of Inertia (rigidity): 43.3% less
- Perimeter (surface area): 60.4% more

**Conclusion:** the fluted barrel is much lighter, much less rigid, and has much more surface area than a solid barrel of the same
**diameter**.

**0.850" Fluted vs. 0.7005" Plain**:

- Cross-sectional area (weight): *same*
- Area Moment of Inertia (rigidity): 25.2% more
- Perimeter (surface area): 94.6% more

**Conclusion:** the fluted barrel is significantly more rigid, and has much more surface area than a solid barrel of the same **weight**.

**Notes:**

* All section properties are courtesy of the 2D Properties module of Ashlar Vellum 3D version 2.70 (my favorite CAD program), based on my layout of the sections.

* Measurements of the 700VS were taken from an actual 700VS from my personal collection.

* I didn't actually have a 700VS on hand, but have recently compared one to a 700VS side by side (while deciding which to buy), and verified that the barrel outside diameters are the same. Flute dimensions are approximate, but should be fairly accurate. After ten years as an engineer, I have a good eye for dimensions; I know for sure that the flute width was much more than 1/8", and definitely less than 1/4"; 3/16" should be quite close. Likewise, I noted for certain that the flutes were full radius, and deep enough that the radius started approximately 3/32" below the outside diameter. Despite any minor errors, the fluted barrel described is certainly representative of the Real World, and the trends are quite clear from the analysis; the effects of fluting are significant. A 1/16" here or there would not noticeably change the results.

* The weight and surface area comparisons hold true only for the *fluted portion* of the barrel. On every fluted barrel I've seen, the fluting does not begin until well forward of the chamber (6"-9"), and ends from 1"-4" from the muzzle. For example, on the Remington barrels presented, only approximately 65% of the barrel is actually fluted, so you will only realize ~65% of the weight savings and surface area increase. Also, I've seen some fluted barrels where the fluting is more shallow and/or narrow than the examples presented. Hence, the effects of the fluting would be less than reported above.

* I also did a quick analysis of a fluted barrel with shallower flutes; I won't present the entire analysis here, but in summary, a barrel of the same weight also had a larger diameter, and the differences in stiffness and surface area were simply less pronounced than the barrel detailed above. Extrapolating: as the flutes become smaller, the effects diminish; as the flute dimensions approach zero, the fluted barrel (and the barrel of the same weight as the fluted barrel) simply becomes the original bull barrel, and there's no effect. Conversely, as the flutes get larger, the effects become more pronounced; eventually, though, one would run up against a geometrical limit (the flutes colliding, or reaching the bore). Under **NO** geometrically possible conditions can flutes make a barrel **MORE** rigid than a plain, unfluted barrel of the same diameter.

* Before someone asks: no, the *number* of flutes has no real effect on these conclusions. Four (or fewer) flutes of the same size would simply remove less material and hence reduce the effects shown. Eight (or more) flutes might increase the effects, but would tend to collide more easily (less room for material between the flutes), so in reality they would tend to have less depth, and hence limit the effects achievable.

--Gryffin

gryffin@gryffnet.com

*Editor's Note: A fluted barrel has much less rigidity than a plain barrel of the same diameter, and more rigidity than a plain barrel of the same weight. But those comparison barrels are not, cannot, be the same. The plain barrel of "same weight" will have a necessarily smaller diameter than the corresponding fluted barrel. The material in the fluted barrel is arranged, due to its greater major diameter, more advantageously to resist bending than the plain barrel's material. So you can have your cake or you can eat it, but not both!*

Hope this helps!