Barrel Trends

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AlanF
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Barrel Trends

#1 Postby AlanF » Sun Oct 11, 2020 6:50 pm

In the last few years, I've heard of more F-Open shooters in particular, changing from 5 groove canted land barrels to 4 groove square lands. What is it about 4 grooves that makes them preferred by a significant number of leading shooters? Is it a general impression about their accuracy, or are there more specific reasons e.g. ease of cleaning, higher velocities etc?

Quick
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Re: Barrel Trends

#2 Postby Quick » Sun Oct 11, 2020 7:14 pm

Ive had a bunch of 4 Groove barrels, 2x square land 5 groove and a 5R. The square land barrels all shot very well. My 5R was a pain to get to shoot. I trust 4 groove and the square land 5 groove.
Shaun aka 'Quick'
Yanchep, Western Australia

308 Win F/TR & F-S
7mm F-Open Shooter.

Gyro
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Re: Barrel Trends

#3 Postby Gyro » Mon Oct 12, 2020 3:34 pm

AlanF wrote:In the last few years, I've heard of more F-Open shooters in particular, changing from 5 groove canted land barrels to 4 groove square lands. What is it about 4 grooves that makes them preferred by a significant number of leading shooters? Is it a general impression about their accuracy, or are there more specific reasons e.g. ease of cleaning, higher velocities etc?


Ya takn the piss Alan yeah ? Considering how many variables there are re why the gun is or isn't shooting surely it's going to be bloody hard to know if it's barrel type x or y that's responsible ? If it's a "hummer" then ya got a good one ......

bruce moulds
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Re: Barrel Trends

#4 Postby bruce moulds » Mon Oct 12, 2020 5:09 pm

what i don't like about canted lands is the possibility that cleaning patches and brushes tend to skid over them, rather than rotate with the twist.
square rifling takes the patches and brushes with it.
canted lands will show you how good the bearings in the rod handle are!
in terms of trends, there are more brand choices now, and there is a trend towards faster twists.
the main trend is the upward spiral in cost relative to earning capacity.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880
http://youtu.be/YRaRCCZjdTM

KHGS
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Re: Barrel Trends

#5 Postby KHGS » Mon Oct 12, 2020 5:17 pm

I was going to let this one pass, but what the hell!!! In my 40 + years as a full time gunsmith, I have fitted them all and just like everyone I have a favourite rifling form. However having said that I can assure everyone that the rifling form has no effect on raw accuracy in a no or light wind condition. However there is no doubt in my mind rifling form has an effect on the way a projectile is affected by wind in flight. I am sure most experienced shooters have owned or seen a barrel that seems less affected by wind, this is caused by the form of the rifling in the barrel launching the projectile, by the way the number of lands and grooves make little difference. These are my observations for what they are worth.
Keith H.

Tim L
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Re: Barrel Trends

#6 Postby Tim L » Mon Oct 12, 2020 5:39 pm

bruce moulds wrote:what i don't like about canted lands is the possibility that cleaning patches and brushes tend to skid over them, rather than rotate with the twist.
square rifling takes the patches and brushes with it.
canted lands will show you how good the bearings in the rod handle are!
in terms of trends, there are more brand choices now, and there is a trend towards faster twists.
the main trend is the upward spiral in cost relative to earning capacity.
bruce.

Totally with you on brushes riding up the side of canted lands, maybe only the first inch or so until enough bristles are in to drive the brush round especially if using a tube style bore guide that's tight on the brush. I did find mine was much easier to clean though.
I'm running a 3 groove, square, 1:9 30cal atm. It is also easier to get clean than a 4 groove square cut.
All the barrels shot as well as one another though so I agree with Keith too.

bruce moulds
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Re: Barrel Trends

#7 Postby bruce moulds » Mon Oct 12, 2020 5:44 pm

keith,
what type of rifling is better in the wind?
i think stability can have that effect too.
precession and nutation are not your friend in the wind.
but we have to live with it.
another trend that comes to mind.
when i started, i used heavy varmint profile at 28" because that was max length before paying extra per inch.
those lighter barrels gave more pronounced oscillations in ladders, making picking a node really easy.
then barrels became straight approx 1.25"diameter at 30'
now 32" straight seems to be the go.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

KHGS
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Re: Barrel Trends

#8 Postby KHGS » Mon Oct 12, 2020 6:24 pm

bruce moulds wrote:keith,
what type of rifling is better in the wind?
i think stability can have that effect too.
precession and nutation are not your friend in the wind.
but we have to live with it.
another trend that comes to mind.
when i started, i used heavy varmint profile at 28" because that was max length before paying extra per inch.
those lighter barrels gave more pronounced oscillations in ladders, making picking a node really easy.
then barrels became straight approx 1.25"diameter at 30'
now 32" straight seems to be the go.
bruce.


My preference would be for a three grove form with shallow lands, lands and grooves of similar width. My second (close) choice is for polygonal rifling. Both of these forms while requiring diligence with cleaning rod control, will not foul as much as other forms while reducing bullet engraving (deformation) so projectile performs better in wind. The trade off is rod rotation must be carefully controlled, as someone once said there are no "free lunches". Again, my observations so make of it what you will.
Keith H.

Gyro
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Re: Barrel Trends

#9 Postby Gyro » Tue Oct 13, 2020 6:45 am

Clocking up a 3 groove barrel with an indicator rod for a "thru the headstock" install is a bit wierd and much harder to get the DTI to run still. Guess it's still gonna be within a bulls roar.

williada
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Re: Barrel Trends

#10 Postby williada » Tue Oct 13, 2020 11:32 pm

Bruce, what you say about precession and nutation is true. Boatright corrected the theory as to how this occurs which has him a nose in front of another ballistician often used in dispatches. People follow fashions until they are tested. Early field class shooters initially followed shortrange benchrest winners until thinkers dispelled some some practices that were not optimum for long range shooting e.g. where the lower end of gyroscopic stability was all the rage and of course we know boat tailed bullets offer less drag. In long range, with Boatright's more accurate analysis of how bullets fly, a tad faster spin has since proved more desirable for gyroscopic stability in long range shooting in a variety of environmental conditions.

Let's tease out some variables. Back in the day, (1980's), I conducted experiments for a barrel manufacturer where we tested all sorts of internal configurations. Suffice it to say, opposing lands and grooves (even numbered lands and grooves) was thought be relatively detrimental to jackets and cores (in theory) compared to non opposing lands and grooves (odd numbered lands and grooves). I could not see any statistical justification on the target with the issued ammunition we used at the time between odd an even configurations. Now, that ammo had harder jackets than what we use today and chronographs had up to 5% error factor. It may need re-examination with better technology.

Technically, you only need sufficient rifling to rotate the projectile. Perce Pavey gave me a two groove .303 barrel. Keith's reference to 3 groove is sound. Denis Tobler was an early advocate of 5 grooves. Whatever land configuration, manufacturers vary the volume of lands and groves according to a land bore volume ratio which tends to remain constant for a given projectile. Harder jackets of military projectiles require deeper land to engrave effectively. To prove the effectiveness of the land bore ratio I used a barrel we made with a shallow land height of .0015" and won a championship with it. The barrel life was short lived.

What is critical, in a good barrel is that the bore dimensions do not open over the length of the barrel and that the twist rate is constant. Keith's 3 groove barrel would be easier to lap to dimension and so maintain gas seal and if measurable, maybe less jacket distortion and more stability. We used a special tool to measure for twist variation. I am not a fan of gain twin barrels using high velocity ammunition. That's a another story.

When remediating worn barrels, and lapping to dimension, I have found the square land shape to be more responsive. Nothing wrong with 4 groove traditional barrels which can out shoot the pilot anyway.

While canted lands may offer slicker velocity, fouling removal may be problematic with age as the barrel wears. That narrow leading edge wears more quickly and may present cleaning issues depending on the guy doing the cleaning. I note with interest, Bartlein is offering a harder barrel. Like that shallow land barrel I used, they are a delight to shoot before wear sets in which can alter critical dimensions that match the bullet. It becomes a rich man's sport at the top level using fresh gear.

Length matters because it affects fundamental harmonics.

Gyro, the trade trick is to insert a firm pilot into the bore and indicate on the inside of it. Takes out the wobbles.

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Re: Barrel Trends

#11 Postby Gyro » Wed Oct 14, 2020 4:01 am

I hear u williada. Just out of curiosity were your barrel installs "back in the day" done thru the headstock with attention being paid to the bores curvature or between centers, with no accounting for same ?

williada
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Re: Barrel Trends

#12 Postby williada » Wed Oct 14, 2020 9:53 am

Gyro, I started using headstock chambering around the time I was engaged by the NRAA to conduct Project Penumbra early 2000's some 3 years before a Palma Match which was a supplementary study into .30 cal barrels I was doing in the 1980's, specifically to find the most appropriate internal dimensions and twist rates suited to the Sierra projectile used at the time. Those dimensions have stood the test of time were used by international competitors in TR. With regard to barrel indexing, and curvature, been doing that from 1980's and written about it for years. Chambering between centres does not account for barrel curvature. I qualify that by saying it is the last six inches that matters and where that is pointing. Allied to that is the bore may wander internally and the wall thickness of the barrel may vary a tad. That may be caused internally by drilling and reaming, but I would say mostly by tapering the outside with wrong rake angles and pressure and depth of cut. I prefer straight taper barrels for good reason and they also produce a more even sine wave for tuning purposes. Some barrels have variable land height for numerous reasons and care has to be taken by simply looking at the job at hand and where you indicate from or centre from on setup. But I can say, early masters were onto it a century before. My goal in providing information over the years has been to level the playing field, where technology was not an advantage over marksmanship. Too many have claimed skill when the rifle was doing the talking. With the gear we use now, the differences have become marginal, and as Alan has been advocating, to win, more attention has to be paid to reading conditions.

I omitted from the previous post, that when a projectile is in flight, it has a boundary layer of air surrounding it and the number of lands and grooves have no impact on drift once the bullet has stabilized. The issue is one of bullet imbalance caused by setup. Also did testing back with project Penumbra on leade angle and I see advocates in FTR using a specific whizz bang angle that we settled on way back and was used by some members of the Ozzie team. But in those days the best gear was not mandated for the team. Individuals did their own thing in ignorance. Does not happen today. The lead angle also affects barrel lift and harmonics. So when teasing apart cause and effect on group, there are a lost of variables and trade offs to make even to the point the shooting platform needs to be considered in relation to the individual's body mass and size of limbs and head position i.e. where that mass is distributed. All affects barrel lift and that can be made specific for distance. The "Sticky" post on this site discusses some of those issues. There is something new to learn everyday, that is why the sport is so challenging and rewarding.

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Re: Barrel Trends

#13 Postby Gyro » Wed Oct 14, 2020 3:56 pm

So can I presume williada your gravitating to the “thru the headstock” barrel install was due to your greater understanding of its benefits ?

williada
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Re: Barrel Trends

#14 Postby williada » Wed Oct 14, 2020 6:27 pm

Gyro, there are lots of subtleties with the setup including the type of reamer holder, whether you pre bore or not, whether you use the tailstock for alignment or an adapter in the toolpost. Each to their own. I am of the philosophy the bullet should start straight at the throat, and that the shoulder should be perpendicular to the bore axis in that area and likewise the threads. It may likely assist a smooth flow of barrel vibration which may impact on harmonics. The easiest way for me to achieve that alignment was to chamber through the headstock in a four haw chuck with a cat's head attached to the spindle at the other end, indicating at the throat.

RDavies
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Re: Barrel Trends

#15 Postby RDavies » Wed Oct 14, 2020 7:14 pm

Sounds like I am falling behind in trends. I think pretty much all of the 15 or so barrels I have had fitted in the last 7-8 years or so have been 5 groove canted lands. The vast majority have gone on to shoot great, with I think only one not performing (copper fouling). Maybe I just got lucky?


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