Posted: 9/15/2007 5:44:08 PM EDT
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I was thinking of having my 24" DPMS bull barrel fluted. Who would you guys recommend ?? |
What kind of FF tube/handguards do you have? What is the profile of the barrel? How much would fluting be vs. having the barrel reprofiled? |
Stock FF. What do you mean profile of the barrel ? What would be done if the barrel was re-profiled ? |
So you would consider that fluting increases the surface area and cooling of the barrel ? |
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Compass Lake Engineering lists fluting on their price list here. I've never used their services, but Frank White is highly respected in the Highpower community. |
| Do not fix what is not broken. I had the most kickass, accurate AR I have ever shot, a 20" ArmaLite National Match A2 that was built during the ban and had the clamp on front sight. Well, I decided after the ban ended to get the pin on sight...no big deal, right? My accuracy went from 3 shot groups at 100 yards with all holes touching, with open sights, to looking like the target was shot with a shotgun. The accuracy never did come back. |
Allow me to throw this out there. Those that tend to hang 3 lbs of steel off the end of their barrel can also benefit from the increased stiffness. |
Correct fluting does 3 things: 1. Increases surface area, thus cooling 2. decreases some weight 3. adds to the rigidity of the barrel |
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Wrong. Fluting does not increase the stiffness of a barrel. Use some common sense - how can you remove material from a barrel and expect it become stiffer? Adding fluting reduces the stiffness. Every time. It's physics. Given two barrels of the same weight, the fluted barrel can have a larger outer diameter, hence greater stiffness (if the fluting geometry and barrel length are selected correctly). Given two barrels of the same outer diameter, the fluted barrel will have more surface area and better convection of heat to the atmosphere. The unfluted barrel will be stiffer. Fluting an existing barrel is probably a bad idea because it causes the the bore diameter to become larger under the flutes. It might work if there is enough unfluted length with choke before the muzzle, otherwise accuracy is destroyed. Whether there is practical weight reduction depends on the flute geometry, but reducing the overall diameter will take off weight more effiently. Fluting a custom barrel that has been hand lapped is a bad idea. |
I dont know why it is said to increase rigidity. My buddy I went to high school with makes all of POF's barrels and he told me that. Ever heard of them? Maybe hes full of shit. |
Nope, never heard of POF. Your high school buddy is either full of shit, or he didn't adequately explain what he meant, or you mis heard what he said. The thing is, I have no shit mechanics on my side, not hearsay or marketing hype. |
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I assume AeroE stands for aerospace engineer. So Im not going to argue with a rocket scientist about building rockets. I was just making a statement. Thats all. It doesnt make sense to me why fluting would add to rigidity of a barrel. Your explanations seems plausible to me. I was just repeating what I learned from a trusted source on my end. |
My physics degree will stand behind AeroE's statements 100%. UNLESS the fluting was forged, which they never are. |
While also causing it to heat up faster. |
Explain how forging changes the stiffness. The stiffness of metals is not affected in any siginificant way for engineering purposes by the processing method. The strength at yield or fracture may change in conjunction with the correct heat treat process, but not the stiffness, expressed as Young's Modulus for our needs. Forging can produce favorable grain orientation in some shapes, particularly where good mechanical properties transverse to the length of the stock material are required. Whether a fluted barrel heats up faster than a plain barrel depends on the geometry and rate of fire. There is some equilibrium point where two barrels of different geometry can maintain the same temperature at different rates of fire, and another set of geometries where one is fluted and the other not that will maintain the same temperature at the same rate of fire. |
| If your gun is not fluted from the factory I would say forget it, it is not worth the trouble/expense for some small gains. Outfits like Quality Parts Corp/Bushmaster machine the longitudinal grooves before they ream/rifle the barrel. Fluting the barrel after the ream/rifle-ing the barrel could distortion in the bore which could lead to inaccuracies. |
Yep |
| I'm on the side of fluting a heavy barre. However it is worth the expense of having it Chryo treated afterwardfs though. DPMS did a great job of both on a setup for me. Good price, great service. I don't know what it was shooting beforehand, but it's now sub-MOA. |
You'll have to get that photo hosted on a server. |
Flute fight?! -Hmm...  No, fluting does not increase, or for that matter, retain the stiffness of the major barrel diameter (despite what you may have seen in print from certain prominent gun-writers); it can only decrease stiffness. Also, with the majority of fluted barrels, weight loss is minimal. How the myth that fluting somehow increases, or retains, the stiffness of a given barrel's major diameter, managed to hijack common sense -is beyond me. What fluting can do; dissipate heat, was already correctly expounded upon in previous posts in this thread. The pics show an extreme example of this principle, where radically deep, radial fluting, is utilised to rapidly disperse heat before it can distort a relatively light (.710" groove diameter/1.000" major diameter, un-tapered) barrel. By turning the entire barrel into a hyper-efficient radiator, its accuracy is preserved, without adding barrel mass for the purpose of resisting distortion. |
Regarding your original question: Select a maker of good quality barrels, have it headspaced to a fresh receiver, then purchase the entire, brand-new upper. It could well be that, as others have implied, that you'd likely be out of about the same money. |
+1 Any machining done on the barrel after it's rifled is FAR more likely to have a negative effect on accuracy than a positive or neutral effect. |
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+1 what AeroE and Troy said. Stiffness will be less than the original barrel. The actual increase in stiffness over an unfluted barrel of the same weight is very small. Decrease in weight vs. the original barrel is also very small. Let me add that heat is transfered by conduction. convection and radiation. Surface area is important only when there is a convection effect, such as air or liquid actually flowing over a surface. Since most rifle barrels will be cooling by radiation, only projected, not actual, surface area is important. Projected area is the same for both. Thus negating any benefits of fluting. I must admit that I have never run the actual finite element analysis of either the heat transfer or the stresses of fluted vs. unfluted. But I have done the weight and moment of inertia calculations of both, and convinced myself that fluting is worthless. My $.02. |
Radiative heating is the most inefficient mechanism in this case; the temperature difference between the barrel and the atmosphere is very small. The great majority of heat will be lost by convection to the air. Conduction will just move the heat around in the rifle components for the most part. The conductive loss to the air will be much smaller than the convective part, and much larger than the radiative part. |
Take a 20" HBAR barrel. Flute it and weigh it. Let's say it comes in at 1.75 pounds. Now, take another 20" HBAR, chuck it up on a lathe, and turn it, reducing its profile slowly until the weight of the barrel reaches 1.75 pounds. (NOTE: it won't be anywhere near as thin as an A1-profile barrel.) NOW you have comparable barrels: both are 20" and both are of the same weight. The fluted barrel is going to be stiffer than the profiled barrel, because it will have a larger overall diameter with metal extending out to that diameter. Both barrels have the same AMOUNT of metal now, but the fluted barrel will have a better arrangement of the metal for both stiffness and cooling. But... properly fluting a barrel increases costs, and it doesn't make a huge difference in usable accuracy unless you normally run your barrels very hot. The flutes add surface area for cooling, but you won't notice a great deal of difference unless you have significant airflow over the flutes to help draw away the heat. -Troy |
Depending on the weight of the tube, you may save as much weight by going to a lighter tube or rail. By profile, I meant thickness. I missed where you said bull barrel, so that is .963 I think. You might be able to get the barrel turned down to a smaller profile, say .750, and that would save a lot of weight. www.ar15barrels.com |