Do the number of lands / grooves matter when it comes to accuracy?

[scythefwd]

Guys, I just checked the number of grooves / lands in my barrel. 8 of each. So I started to question, does the number of lands / grooves matter in a barrel after a certain extent? I know that Ed Shilen has some 5 land barrels, so whats with the high number? Any one care to educate me more on the purpose of them (besides adding spin and stability to the bullet)?

 

[taliv]

that's an interesting question I haven't heard before. I've heard a lot of discussion about the geometry of the lands and canting them, etc but not the actual number.

The only effect I can think offhand would be that more lands/grooves means more surface area, right? which means more friction

 

[rbernie]

I would ordinarily have thought not. However, several recent efforts to increase the performance of 6.8SPC have decreased the number of lands/grooves as well as reduced the twist rate. Both of those changes were touted as reducing resistance and shot-to-shot consistency.

 

[rcmodel]

The military used two lands and grooves on the 03A3 Springfield during WWII.

I have one I sporterized in 1964 that will shoot well under 1 MOA with various handloads it likes.

There was some thought that they would last longer before losing accuracy then the earlier four land & groove barrels.

My feeling is that the number of lands & grooves is far less important then if the hole is the same diameter all the way through, and very very smooth.

rc

 

[Carl N. Brown]

Theoretically, more, narrower and shallower grooves distort the bullet less than fewer, deeper and broader grooves. The excellant accuracy I have gotten with Marlin rifles in .30-30 and .22 with Microgroove barrels seems to bear this out. On the other hand, Julian S Hatcher makes a convincing argument that the economy measure of producing .30-06 barrels in WWII with only two grooves did not result in a significant loss of accuracy. I suspect that attention to consistency has more to do with accuracy than the number of grooves.

 

[Slamfire]

The skill of the barrel maker counts for more than the number of grooves.

Hopefully a machinist can comment, but I believe an even number of lands/grooves would be easier to cut with a button or a broach. Rifling is a cut spiral, I can imagine that asymmetry in a cutting tool would cause issues.

For hammer forging, I would guess that symmetry in the bore would help keep the bore circular. But I don't know.

Even lands/grooves were probably easier to measure with a mechanical gage. (Remember "Star Gages"?) Probably not an issue once air gages came out.

From what I read, the british ran erosion tests with various rifling configurations. They picked five groove rifling for the P13 rifle as the best. I know the US military ran erosion tests, but I don't know what their conclusions were.

I have seen rifling at the end of 16" cannons, there was a lot of rifling in those tubes.

 

[jerkface11]

Fewer lands and grooves will make it easier to clean. Nothing to do with accuracy though.

 

[highorder]

Hopefully a machinist can comment, but I believe an even number of lands/grooves would be easier to cut with a button or a broach. Rifling is a cut spiral, I can imagine that asymmetry in a cutting tool would cause issues.

Actually, asymmetry in tooling is often desirable, as it reduces the possibility of tool failure along a symetrical axis.

You will frequently encounter milling cutters with 37teeth, 85 teeth, etc.

 

[MCMXI]

Both of my Krieger barrels are the four groove variety. Here's what Krieger has to say about the number of grooves.

Q: Does a barrel with more grooves shoot better or last longer than a barrel with less grooves?

A: No. Virtually none that we can find though it might make a difference in a button-rifled barrel. But a button-rifled barrel still on average will not last nearly as long as a single-point cut-rifled barrel.

The only effect I can think offhand would be that more lands/grooves means more surface area, right? which means more friction

The increase in surface area (as a % of the smooth bore) would be minuscule at best. The increase would be something like 2 x land height x barrel length.

 

[MissouriCrowinMass]

You guys ever hear of a rifle barrel that could change from 6 lands & grooves to 4?

I know one.

 

[Carl N. Brown]

A friend of mine had an antique 11mm rifle that had been sleeved at the chanber and throat to fire .45 ammo using a section of .45 pistol barrel. It too had an abrupt change in number and depth of grooves as the bullet went down the sleeved barrel and transitioned into the original barrel. The .45 chamber/barrel insert had been turned down on a lathe to sleeve the original rifle chamber and as I recall was removable. We suspected it had only been used with .45 blanks as a ceremonial gun.

 

[rangerruck]

as mentioned, marlin uses microgrooving, for less bullet deformation as it moves downt the bbl, which on paper translates to better accuracy.
Remmy makes a custom shop sniper type rifle, that guarantees sub moa accuracy, and it is a 5r, as opposed to their normal 4.
i would say myself, the answer is yes and no: it more depends on anything, that you keep the depth/height of the l's and g's , super consistent. And secondly, the twist; you do not want the twist speeding up, then slowing down, inside the bbl. either keep it super duper the same speed, or slowly gain twist it, but again, you need to be really consistent in the gain.

 

[Jim K]

The change from 4 to 2 grooves in WWII was strictly to speed production, as most barrel makers were still using scrape cutting, and going to 2 grooves cut rifling time in half. With a button or hammer forging, it doesn't matter once the button or mandrel is made, rifling the barrel takes the same time whether there are 2 grooves or 20.

Jim

 

[Maverick223]

My feeling is that the number of lands & grooves is far less important then if the hole is the same diameter all the way through, and very very smooth.

I agree...as long as the lands and grooves are equal in number you are good to go...if not somebody really messed up.

as mentioned, marlin uses microgrooving, for less bullet deformation as it moves downt the bbl, which on paper translates to better accuracy.

I don't believe that it makes a great deal of difference, with the exception of rimfire cartridges. I have always figured that the microgroove barrels should wear quicker too...but that too is not a really big concern with the rifles that it is likely to be chambered in.

 

[MCMXI]

My Marlin 1894 has Ballard rifling.