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maccluer
08-11-2013, 05:54 PM
I drew a certificate for a Hart barrel at the 2013 IBS Group Nats last week. I thought it might be interesting to take a flyer: What has been the experience with fluting a HV contour barrel in order to make LV weight? The increased stiffness would decrease max longitudinal displacement but increase muzzle tip frequency. Surely someone has tried this before?

B.Larson
08-11-2013, 07:17 PM
Skip Otto fluted all barrels in later yrs. except for rail gun barrels....It works....

alinwa
08-11-2013, 09:22 PM
HOW you flute may make a difference. Some are wide, some narrow. Some are straight, some helical. Some use a ball end mill, some a sidecutter and some a fiber blade. Others grind the flutes. I don't think they all yield same results.


opinionby



al

Charles E
08-11-2013, 11:05 PM
One thing about Skip -- he had his own horizontal mill & barrel fluting operation, so it didn't cost him anything...

You can probably argue about whether it hurts or maybe helps until the bovines settle down. General consensus *probably* is, not worth it unless you already have the barrel & need to make weight. Meaning fluting follows an "oops" moment rather than an "ah" one.

FWIW

Boyd Allen
08-11-2013, 11:23 PM
A couple of thoughts:

Just because stiff is good does not necessarily mean that stiffer is better...does it?

If we are trying to have all of our bullets with the barrel in the same segment of its vibration pattern, given that this is a timing thing, and that short range benchrest loads are not known for their small ESs, wouldn't increasing the frequency of vibration make the target segment harder to stay within?

maccluer
08-12-2013, 12:00 AM
If I understand what Boatwright says, the dominant effect is not tip deflection but the vertical velocity imparted to the bullet as it exits. Additional stiffness moves the (first mode) node outward and increases frequency. These work in opposite ways on vertical imparted velocity. A computation is in order.

Damon
08-12-2013, 12:16 AM
The trouble is that the flutes decrease the stiffness faster than they decrease the mass, and so you get a decrease in frequency.

I'm not smart enough to know if that's good or bad. Could be either or neither, but it is certainly different.

Boyd Allen
08-12-2013, 12:43 AM
I would think that if two barrels weigh the same, and are the same length and caliber, the one that is fluted, and larger in diameter, should be stiffer than the one that is not fluted and smaller in diameter...and that resonant frequency, of a given length, should vary with stiffness. On the other hand, if you flute to a lighter weight....I don't know. I do know that one of the better shooters around the short range benchrest game has a steel and rubber lump threaded on the end of his barrel that undoubtedly slows something down, and does not seem to be hurting his results. I seem to remember something being said about broadening nodes.

Damon
08-12-2013, 08:02 AM
I would think that if two barrels weigh the same, and are the same length and caliber, the one that is fluted, and larger in diameter, should be stiffer than the one that is not fluted and smaller in diameter...and that resonant frequency, of a given length, should vary with stiffness.

That's correct. If you make it lighter instead of keeping the weight the same, then you lose stiffness faster than mass, and the frequency goes down.

mks
08-12-2013, 09:22 AM
I would think that if two barrels weigh the same, and are the same length and caliber, the one that is fluted, and larger in diameter, should be stiffer than the one that is not fluted and smaller in diameter...and that resonant frequency, of a given length, should vary with stiffness.

Correct, the resonant frequency scales like the square root of EI/M, where E is Young's modulus, I is the moment of inertia and M is the mass. A fluted barrel has higher I compared to an unfluted one of the same weight. Increasing frequency is not necessarily a good thing if we want to tune a barrel. In fact, decreasing frequency seems to be better for the typical centerfire BR rifle. Increasing mass by adding a tuner can help by decreasing frequency.

Also, the dominant factor in tuning is not muzzle displacement or muzzle velocity imparted to the bullet, but muzzle angle. The muzzle is typically displaced by only a few thousandths when the bullet exits and the muzzle velocity is small compared to the gravitational acceleration that acts on the bullet after it leaves the barrel. But a small change in muzzle angle makes a big difference at the target. A minute of angle (1/60 of one degree) changes point of impact by about an inch at 100 yards. The angle change needed to tune a barrel over a typical ES is 'way less than a minute.

Greg Walley
08-12-2013, 10:18 AM
I drew a certificate for a Hart barrel at the 2013 IBS Group Nats last week. I thought it might be interesting to take a flyer: What has been the experience with fluting a HV contour barrel in order to make LV weight? The increased stiffness would decrease max longitudinal displacement but increase muzzle tip frequency. Surely someone has tried this before?


Years ago, I asked a top BR barrel maker about fluting barrels for short-range BR competition. He said he didn't like the idea at all. When I asked him about fluting being the only option for a particular situation, he said "take off as little as possible".

If you think about how a BR barrel is made, it only makes sense not to flute. Worrying about vibration and stiffness is barking up the wrong tree.

Greg Walley
Kelbly's Inc.

Damon
08-12-2013, 12:56 PM
In fact, decreasing frequency seems to be better for the typical centerfire BR rifle.

Do you have any more info on that? In Rifle Accuracy Facts, Harold Vaughn described some experiments that involved sleeving barrels with lead for exactly this reason. Unfortunately, he did not go into much detail, and he ran into mechanical problems with the lead. Ever since reading that, I've wondered about what's going on there. Is it just a matter of being easier to tune if you can get the frequency down?

SGJennings
08-12-2013, 02:09 PM
"mks", Keith Sharp, is a sharp cookie, if you'll pardon the pun.

We had an email discussion about this recently. The bottom line is as stiff as possible in the horizontal plane and less stiff in the vertical.

Damon
08-12-2013, 03:00 PM
"mks", Keith Sharp, is a sharp cookie, if you'll pardon the pun.

We had an email discussion about this recently. The bottom line is as stiff as possible in the horizontal plane and less stiff in the vertical.

So when are we going to see oval cross sections?

mks
08-12-2013, 03:03 PM
Do you have any more info on that? In Rifle Accuracy Facts, Harold Vaughn described some experiments that involved sleeving barrels with lead for exactly this reason. Unfortunately, he did not go into much detail, and he ran into mechanical problems with the lead. Ever since reading that, I've wondered about what's going on there. Is it just a matter of being easier to tune if you can get the frequency down?

Decreasing frequency may not help every rifle, but when you get down to it, every HV and LV contour barrel is pretty much the same, only the length varies. And there are not huge differences in stiffness of the stocks that are typically used. Thus their responses are likely in the same ball park. That's why VarmintAl's simulations are probably fairly universal for short range BR rifles. The points of impact in the simulations have been validated against a real rifle, so Al's model is as reliable as the available data allows.

The results show that without a tuner, the bullets exit near the peak of the muzzle projection curve. Not a bad place, but the best is on the upward slope. To get to the upward slope, we need to slow down the rifle's response, which means reducing natural frequency. (An alternative is increasing bullet speed, but that may impact accuracy.) Adding the mass of a tuner gets us to the upward slope.

Furthermore, we would really like the upward slope to be steeper for full positive compensation. But that is a different discussion.

Boyd Allen
08-12-2013, 03:39 PM
Another modification that Varmint Al did a simulation of was removing some material from the middle of the barrel. To move the bullet release to the left there were three things that got the job done, holding velocity constant; adding weight to the muzzle to slow the barrel's swing; using a longer (24") barrel (not practical for a LV/S); and thinning the middle of the barrel, an idea that I had suggested to him, that was not original to me. Merrill Martin did an experiment that was published in the pre-color days of PS where he combined that, and shaft collars at the muzzle to tune out the vertical difference between standard and HV .22 rimfire ammo at 50 yards. Also if you look at a picture of one of Calfee's xp100 .22 rimfire conversions, you may see that he thinned down the barrel in the center, which I believed allowed him to use a lighter tuner, which helped the balance of the pistol. Some years back, he was involved in a thread on this site in which I pointed this out, and liked my use of the term "hinge point" to describe what he had done. Take a close look at post #3.
http://benchrest.com/showthread.php?67074-xp-100-pistol

Steelhead1
08-12-2013, 05:33 PM
I have two barrels that came with my Teddy Action that are fluted. Both barrels were done by Dwight Scott, and I put a new heavy varmit barrel on as soon as I got the Teddy, never shot either of the fluted barrels.
While at the Springville Utah shoot I had a major problem with my 3L Bat (Case Rupture during practice) which broke the extactor. So I pulled the heavy varmit barrel off the Teddy and screwed on one of the fluted barrels, I had to bum 15 rounds of brass as my brass would not fit. On saturday morning that light varmit barrel shot very well for having no time on friday to find a tune on it. Wound up 8th in 100yd LV. So I would conclude that the flutes had no effect as far as I am concerned and these are deep flutes .150. I think with a little more time in practice and things would have been better!

skeetlee
08-12-2013, 05:53 PM
i just fluted a heavy varmint 30br cut rifled barrel so i could use my NF scope on my score rifle. The barrel shot extreamly well before i fluted it, and the barrel still shoots extreamly well after. I see no difference what so ever. Point of impact did change a bit as exspected, but no issues at all. Now this is just one situation, so its hard to draw a solid picture at his point. Lee

zippy06
08-12-2013, 08:00 PM
Chuck,
Maybe you could trade the HV for a LV barrel ???

maccluer
08-12-2013, 09:19 PM
Greg:
That's probably good advice. But last winter I built up a match-quality AR upper using a White Oak 20-inch fluted squad designated marksman barrel that weighs only 41 ounces. It out shoots at 200 a White Oak heavy service match upper, although to be fair I used the much stiffer DPMS competition receiver. I'm tempted to give the fluted HV to LV a try.
Chuck

maccluer
08-12-2013, 09:28 PM
Chuck,
Maybe you could trade the HV for a LV barrel ???

At this point I haven't ordered the barrel from Hart. Waiting for Dwight S. to return from Bonneville flats.

jlcprec
08-12-2013, 10:07 PM
I've fluted a lot of barrels the last few years with the advent of the heavy scopes. I've taken off anywhere from 2 oz. to 12 oz. I never had a barrel that was really bad after all that. Some were fluted before shooting and some after I saw how they shot. I've never seen that fluting hurt the barrels potential. I can flute my own, so my situation is different from most, but I would rather flute to remove a few ounces that cut the muzzle off. I think you have more potential to make a good shooter into an average barrel doing that than by fluting. (on the other hand, cutting some off might make it better, who knows?)

I like to do a lot of small flutes vs. fewer deep flutes. I do 10 flutes on a varmint barrel.

Jim Carstensen

maccluer
08-14-2013, 12:23 PM
If I understand what Boatwright says, the dominant effect is not tip deflection but the vertical velocity imparted to the bullet as it exits. Additional stiffness moves the (first mode) node outward and increases frequency. These work in opposite ways on vertical imparted velocity. A computation is in order.

I disremembered some basic facts: 1) the modal nodes are not moved when stiffness is changed. 2) the first mode has no nodes. (I was thinking by false analogy to a fly rod.) Stiffness affects only frequency and tip excursion. I refer to my favorite source, a must-own: "Boundary Value Problems and Fourier Expansions" in a low-cost Dover paperback, eqns 8.30--8.33.