Rifle Lands and Effects on Bullet and Group Dispersion

[VA_XTC_Shooter]

I know there has been discussions here especially about 5r barrels, but I came across more information that touches on more than just what I think has been discussed here before, maybe I missed if it was.

I was recently introduced to the work of Jeff Siewert from the Hornady Podcast #78 - Barrels. (43) Ep. 078 - Let's Talk Barrels with Jeff Siewert - YouTube


Mr. Siewert has a book out, Bullets Demystified, I have his book on order to read, but have read through his work available on his website, bulletology.com. One article in particular, Gun Barrel Considerations Gun Barrel Configuration Info v2.pdf (storage.googleapis.com)

There are multiple barrel aspects discussed in this article and podcast, I would like to keep this thread focused on the rifling design aspect. I will make other threads to discuss other aspects of this article for better housekeeping and reference.

Starting on p. 5, Mr. Siewert discusses "Number of Lands and Grooves," "Groove to Land Width Ratio," and "Land Profile." I found his findings/assertions very interesting. As you will see below, each are discussed separately, but are interrelated.

Number of Lands and Grooves - "The higher the number of lands and grooves, the lower the peak bearing stress on the projectile and barrel, and the lower the wear on the driving surfaces acting to spin the projectile while it’s in-bore.” - Siewert

Frank Green of Bartlein Barrels has indicated in a podcast with Erik Cortina (43) Test results - 5 groove vs 6 groove barrels | Bartlein Barrels - YouTube he thought the 5R was gentler on bullets because each land is opposite a groove instead of another land, so in his opinion, exerted less pressure on the bullet. This is also mentioned on the Bartlein Barrels website Rifling | Bartlein Barrels

TC Encore indicates the same sentiment.

http://accurateshooter.net/Blog/krieger5r02op.png

Groove to Land Width Ratio - "Since all projectiles are tipped in-bore relative to the bore centerline, the wider the land (e.g. the smaller the groove-to-land width ratio) the more support the projectile has and the smaller the in-bore angle the projectile will attain in-bore for an equivalent clearance...Since the smallest diameter feature in the barrel (e.g. the land tops) controls the in-bore angle of the projectile relative to the bore centerline, having lands that are narrow is not conducive to keeping the in-bore angles small." - Siewert

He also mentioned in the podcast that the consistency of the groove depth is not as critical. The leakage that could occur is minimal. However, he did indicate that the dimensions of the lands, width, is more important to not affect stability. He also mentioned the same as stated above in his article the importance of having wider lands than grooves.


What is interesting is that Frank Green was discussing 6 groove to be slightly less accurate than the 5R. Well, comparing the profile and land/groove widths, the 6 groove barrels have wider grooves than lands. Could this along with the geometry of the 5R vs 6 groove be a factor? What about comparing to a 4 groove with wider lands than grooves?

riflingprofiles-zps0f29dd06.jpg (800×785) (faxonfirearms.com)



Land Profile - Mr. Siewert, seems to indicate similar sentiment when he discusses land profile "The contact stress generated by rotational acceleration of the bullet stays constant with increases in the direction cosine of the land driving surface, but a considerable shear stress develops relative parallel to the land face, increasing the total stress on the contact surface between the land driving surface and the engraved surface on the projectile jacket...There does appear to be a distinct difference in dispersion (group size) performance between barrels with standard lands versus polygonal lands." - Siewert

While not specifically related to polygonal, in the same podcast mentioned above, Frank Green said that the testing he has seen, the 5R were in that testing "barely" more accurate than a 6 groove. Perhaps this is in line with Siewert’s view on the better accuracy of polygonal, the 5R has “smoother” geometry than traditional grooves, but not as smooth as polygonal.

I am only aware of available polygonal rifle barrels in the US from Schneider and PacNor, any others?



If you read this far, thank you. I know it was a lot, but they are all interrelated. I am anxious to see the discussion ahead.

 

[jackieschmidt]

I think in order to ascertain exactly how the number of lands and grooves and their dimensions affects accuracy, we need to determine the yardages being shot. That is, will the Rifle be used in Short Range Group or Score, or at a longer range, such as those encountered in High Power, Palma, F Class, PRS, and ESLR.

In the Short Range Formats, (100/200/300 yard), decades and decades of trial and error has determined that the number of lands and grooves, their depth and even their shape have little to do with the accuracy and precision potential of a barrel.

We have all seen the “fads” come and go. Someone would start winning with a 3 groove, and all of a sudden everybody wanted a 3 groove. The same can be said of 4 grooves, 5 grooves, 6 grooves, polygonal rifling, ratchet rifling, rifling accidentally produced when the hook tool wasn’t ground correctly. You name it, we have seen it.

In the end, it turns out that the various barrels were just “great barrels”and the number and shape of the lands and grooves had nothing to do with it.

At this time, I would venture a guess that the vast majority of Short Range Group and Score Competitors are using some brand of a 4 groove barrel. Why? Easy to work with, it is a time proven concept, and nothing else in the real world of The Competitive Arena seems to be any better.

Of course, it can be determined that the shape of a given land/groove combination might exert a different amount of stress on a bullet when the initial engraving occurs. But after the bullet takes that initial hit, I doubt it knows the difference.

As for the longer range Disciplines, where down range ballistics plays a much bigger roll in determine where the bullet ends up in the target, that is a much more complicated subject. Since I am not a Long Range Shooter, I have little knowledge of that.

As for any of these configurations affect on a bullet designed for superior terminal ballistics, I would think that it would be a moot point. In a bullet designed to bring down Game in a efficient and humane manner , the shape of the lands and grooves probably is of no consideration. These bullets are designed to have superior terminal ballistic performance combined with sufficient accuracy potential for the shooter to hit the animal at a reasonable distance.

If you think about it, when contemplating everything that can affect a bullet‘s path from the instant the primer is struck to the time it hits the target, the shape or number of lands and grooves are really insignificant.
THAT IS, as long as those lands and grooves are produced to the highest standard and held to the exacting dimensions required in a premium barrel.

 

[VA_XTC_Shooter]

You are correct, I should have mentioned the shooting I am interested in.
I am interested in general knowledge of the subject, but for specific disciplines - highpower, 600-1000 yd shooting.

 

[Acyr]

One point no one talks about is groove depth and its relationship to bullet diameter.
I wonder if he mentions it in his book.
I do agree about his belief that wider lands have benefits.

 

[VA_XTC_Shooter]

As I stated above, he did mention in the podcast groove depth consistency was not a major factor, but not in relation to bullet diameter.
Obviously a groove depth can only be soo deep, I guess the better question is what parameters of land height are a factor?

 

[Acyr]

I am a barrel maker. I make cut rifled barrels for a small barrel company.
Groove depth determines land height. Groove width determines land width. Pretty basic stuff.
My concern with groove depth is that the end user almost never measures it. Everyone measures the bore but how do you know what the groove depth is? The reason I think this is really important is because the bullet needs to fit the groove correctly to perform as expected. Deep grooves are not uncommon in the barrel world.
If you have a bullet with an OD of .3081 and the bore is .3000 but the groove measures .3085 how well do you think it will seal?
I would like to know if anyone has studied this in depth?
Ever wonder why some barrels are fast and some are slow? I think this is why.

 

[sdean]

I am a barrel maker. I make cut rifled barrels for a small barrel company.
Groove depth determines land height. Groove width determines land width. Pretty basic stuff.
My concern with groove depth is that the end user almost never measures it. Everyone measures the bore but how do you know what the groove depth is? The reason I think this is really important is because the bullet needs to fit the groove correctly to perform as expected. Deep grooves are not uncommon in the barrel world.
If you have a bullet with an OD of .3081 and the bore is .3000 but the groove measures .3085 how well do you think it will seal?
I would like to know if anyone has studied this in depth?
Ever wonder why some barrels are fast and some are slow? I think this is why.

Is there an easy way to measure groove depth?

 

[Acyr]

Is there an easy way to measure groove depth?

Not without a good quality tenth reading internal mic. 3 point for 6 groove, 2 point for 4 groove etc.

 

[VA_XTC_Shooter]

I am a barrel maker. I make cut rifled barrels for a small barrel company.
Groove depth determines land height. Groove width determines land width. Pretty basic stuff.
My concern with groove depth is that the end user almost never measures it. Everyone measures the bore but how do you know what the groove depth is? The reason I think this is really important is because the bullet needs to fit the groove correctly to perform as expected. Deep grooves are not uncommon in the barrel world.
If you have a bullet with an OD of .3081 and the bore is .3000 but the groove measures .3085 how well do you think it will seal?
I would like to know if anyone has studied this in depth?
Ever wonder why some barrels are fast and some are slow? I think this is why.

I guess you could cast or slug the bore to measure the groove depth?

There are a couple things we are talking about. You are talking about groove depth and being too deep, it allows leakage around the bullet, or maybe bullet in its plastic form expands to it. If there is one deeper groove than all the others, this could create and imbalance in the bullet, no?

I was talking about similar idea, but the inverse. Could the bore diameter be smaller or larger, thus making the lands shorter/taller?

Then we toss in the number of lands/grooves. I am curious now of the various compression, for lack of a better word, on the bullet from these various combos....does it matter?

 

[gunsandgunsmithing]

Lots of speculation and hard to prove much beyond what the target says but there are some established attributes and qualities that have known values..or changes. One is how pressure builds. Both Bartlein and the(for now) out of business Broughton barrels advised against their 5 c or r rifling in a 6ppc with n133 specifically. After discussing this with Tim North a fair bit, his findings were related to how the pressure builds with that specific combination but said no worries at all with say a 6br and n135, for example. I do know that some are out there and performing well, but this is just what two barrel makers in fact said about that. It was somewhere on Bartlein's site for a while. Not sure if it's still there or not.

Another is land to groove ratio. I don't want to spit incorrect numbers but I think there are well accepted small ranges of this ratio that several makers adhere to, for whatever particular reason with their 4 groove stuff. Not saying there aren't exceptions to this either but iirc, it was Boots Obermeir(sp) that came up with this and it has stayed around the same ratio for a long time.

All that said, I think there may be benefits from testing some less conventional approaches. There's only one way to know what works for sure...testing.

 

[VA_XTC_Shooter]

All that said, I think there may be benefits from testing some less conventional approaches. There's only one way to know what works for sure...testing.

Agreed. I am always looking at things, again, and again. It's like when you read a book again, you pick up new things. I am just doing some research to see which direction I'd like to go and test.

 

[Acyr]

I guess you could cast or slug the bore to measure the groove depth?

There are a couple things we are talking about. You are talking about groove depth and being too deep, it allows leakage around the bullet, or maybe bullet in its plastic form expands to it. If there is one deeper groove than all the others, this could create and imbalance in the bullet, no?

I was talking about similar idea, but the inverse. Could the bore diameter be smaller or larger, thus making the lands shorter/taller?

Then we toss in the number of lands/grooves. I am curious now of the various compression, for lack of a better word, on the bullet from these various combos....does it matter?

In cut rifling you can make the grooves as deep or shallow as you want. The bore size is determined first. You can also make that big or small if wanted.
I don’t know how it’s possible to make one groove deeper than the others. At least not in single point cut rifling.

 

[jackieschmidt]

In cut rifling you can make the grooves as deep or shallow as you want. The bore size is determined first. You can also make that big or small if wanted.
I don’t know how it’s possible to make one groove deeper than the others. At least not in single point cut rifling.

We have to rely on quality barrel manufacturers to insure us what the groove diameter is. As you probably know, Krieger guarantees what the groove diameter will be, and says it will never be larger at the muzzle end than the chamber end.
I can compare one barrel to the next. I have deltronic pins to ascertain the exact bore diameter. When I chuck a blank up, and indicate the lands and grooves, I can watch the tenth indicator drop as it passes from land to groove. When I get the blank running dead true, I can determine, probably within a tenth, the exact diameter of the grooves.
Both Krieger and Bartlien cut rifled barrels are so consistent from barrel to barrel on the groove diameter that it just about becomes a moot point.

The only way a cut rifled barrel could one deep groove is if for some strange reason the machine failed to index and the hook tool took several swipes through that groove. Knowing how yjis process works, I doubt that could happen.

By the way. Do you index your barrels with a CNC head, or do you have Sine Bar Machines.
?

 

[Acyr]

I use a sine bar machine. 6 groove.

 

[D-4297]

Mr. Obermeyer gained much of his knowledge of this , and the 5r design from Russian Barrel-makers during a trip there in the late 1950's . Which is not to say he didn't refine and redesign the whole concept . He did .

 

[Acyr]

Mr. Obermeyer gained much of his knowledge of this , and the 5r design from Russian Barrel-makers during a trip there in the late 1950's . Which is not to say he didn't refine and redesign the whole concept . He did .

The story I got recently from a friend of Boots and also a barrel maker from Wisconsin was the US Gov't asked Boots to study the barrels on some Russian rifles and ammo they had acquired. Boots went on and made a few for himself and a couple of friends who were local sling shooters. They shot so well he started making them.

 

[357Mag]

I know there has been discussions here especially about 5r barrels, but I came across more information that touches on more than just what I think has been discussed here before, maybe I missed if it was.

I was recently introduced to the work of Jeff Siewert from the Hornady Podcast #78 - Barrels. (43) Ep. 078 - Let's Talk Barrels with Jeff Siewert - YouTube


Mr. Siewert has a book out, Bullets Demystified, I have his book on order to read, but have read through his work available on his website, bulletology.com. One article in particular, Gun Barrel Considerations Gun Barrel Configuration Info v2.pdf (storage.googleapis.com)

There are multiple barrel aspects discussed in this article and podcast, I would like to keep this thread focused on the rifling design aspect. I will make other threads to discuss other aspects of this article for better housekeeping and reference.

Starting on p. 5, Mr. Siewert discusses "Number of Lands and Grooves," "Groove to Land Width Ratio," and "Land Profile." I found his findings/assertions very interesting. As you will see below, each are discussed separately, but are interrelated.

Number of Lands and Grooves - "The higher the number of lands and grooves, the lower the peak bearing stress on the projectile and barrel, and the lower the wear on the driving surfaces acting to spin the projectile while it’s in-bore.” - Siewert

Frank Green of Bartlein Barrels has indicated in a podcast with Erik Cortina (43) Test results - 5 groove vs 6 groove barrels | Bartlein Barrels - YouTube he thought the 5R was gentler on bullets because each land is opposite a groove instead of another land, so in his opinion, exerted less pressure on the bullet. This is also mentioned on the Bartlein Barrels website Rifling | Bartlein Barrels

TC Encore indicates the same sentiment.

http://accurateshooter.net/Blog/krieger5r02op.png

Groove to Land Width Ratio - "Since all projectiles are tipped in-bore relative to the bore centerline, the wider the land (e.g. the smaller the groove-to-land width ratio) the more support the projectile has and the smaller the in-bore angle the projectile will attain in-bore for an equivalent clearance...Since the smallest diameter feature in the barrel (e.g. the land tops) controls the in-bore angle of the projectile relative to the bore centerline, having lands that are narrow is not conducive to keeping the in-bore angles small." - Siewert

He also mentioned in the podcast that the consistency of the groove depth is not as critical. The leakage that could occur is minimal. However, he did indicate that the dimensions of the lands, width, is more important to not affect stability. He also mentioned the same as stated above in his article the importance of having wider lands than grooves.


What is interesting is that Frank Green was discussing 6 groove to be slightly less accurate than the 5R. Well, comparing the profile and land/groove widths, the 6 groove barrels have wider grooves than lands. Could this along with the geometry of the 5R vs 6 groove be a factor? What about comparing to a 4 groove with wider lands than grooves?

riflingprofiles-zps0f29dd06.jpg (800×785) (faxonfirearms.com)



Land Profile - Mr. Siewert, seems to indicate similar sentiment when he discusses land profile "The contact stress generated by rotational acceleration of the bullet stays constant with increases in the direction cosine of the land driving surface, but a considerable shear stress develops relative parallel to the land face, increasing the total stress on the contact surface between the land driving surface and the engraved surface on the projectile jacket...There does appear to be a distinct difference in dispersion (group size) performance between barrels with standard lands versus polygonal lands." - Siewert

While not specifically related to polygonal, in the same podcast mentioned above, Frank Green said that the testing he has seen, the 5R were in that testing "barely" more accurate than a 6 groove. Perhaps this is in line with Siewert’s view on the better accuracy of polygonal, the 5R has “smoother” geometry than traditional grooves, but not as smooth as polygonal.

I am only aware of available polygonal rifle barrels in the US from Schneider and PacNor, any others?



If you read this far, thank you. I know it was a lot, but they are all interrelated. I am anxious to see the discussion ahead.

As I stated above, he did mention in the podcast groove depth consistency was not a major factor, but not in relation to bullet diameter.
Obviously a groove depth can only be soo deep, I guess the better question is what parameters of land height are a factor?

VA -

Howdy !

One thing not mentioned a lot so far, is bullet jacket thickness....

I called all of the US barrel makers could find last week, to find out which of them do gain twist rifling. I am considering a new rifle project, intended to propel a .224" cal 55gr varmint bullet w/ a .009" thick jacket @ elevated velocity. I would use a gain twist barrel that features a gain amount presented within an appropriate twist rate range; to keep bullet' rpm @ a level it has already proven able to tolerate....while a!so being hyper-accurate.

Of the two manufacturers that do "gain twist ", I spent the most time talking w/ Bartlein.
My thought is that use of a gain twist barrel could help keep forces exerted on the thinner jacketed bullet @ an acceptable level. The Bartlein rep did not say anything to correct my thinking. In fact, he had owned/ shot multiple gain twist barrels in various calibres.
We spent more time on how to choose the gain rate, and how to spec' the barrel blank; so that finished barrel would feature the gain twist desired....located at correct points along its length.

We also talked about number of lands/grooves, and I was left w/ the impression a
6 groove was recommended over a 5 groove; for use in my accurate varmint rifle project.

Unsolicited, the barrel tech did float the idea of my going w/ a .219" bore diam.
I took that as a suggested adjunct to use of a gain twist, the intended outcome of course being...to reduce stress on the bullet. The representative did not have concerns about ability of the chosen .224" cal bullet to "seal" the bore.


With regards,
357Mag