What effect does the number of grooves have in magnum calibers?

[Darryle]

I have a 24" 3r groove 6.5 manbun that shoots 50-75fps faster than the same length 5r groove barrel. I recall at the time I ordered this barrel that 3 groove barrels were advertised as an easy way to pick up velocity. The Labradar appears to back that up with the various factory ammo I have used.

Now that I am in the process of building either a 270 or 7MM WSM, I am wondering if that same thought applies to magnum calibers with respect to the faster twist rates used these days? Does bore diameter have any effect?

I am also wondering if barrel longevity is affected by the number of grooves? Less grooves equals faster erosion?

Just trying to gain more knowledge on barrel characteristics, so I appreciate you sharing your knowledge with me.

Found this post talking about more grooves helping bullets remain intact, thoughts?

I like the 6 grove Harts or the 5 C Broughtons for a 7mm. Anytime I plan to use an high expansion bullet, best suited for long range hunting, I like more groves with less jacket scribing going on. I feel this will let the bullet hold together better when taking game at closer distances and also why I only use enough twist rate to effectively stabilize the bullet of choice. With all the 7's I have put together the Harts and Broughts have been very accurate to very long distances.

Jeff

 

[aushunter1]

Interesting subject, more groves more spin = less fps or just more groves = more accuaracy??

Would be good to see some side by side comparisons with the same loads!

 

[Tiny Tim]

Tagging in. Great question.

 

[MagnumManiac]

My 4 groove and 3 groove barrels are faster than my 5 groove or 6 groove barrels.
Twist rate does not appear to affect velocity.
As I have shot all of the above in the same calibre/cartridge side by side with differing twist rates and the test can be done on different days with the same results.
Can't say why twist doesn't affect velocity, but groove number all boils down to friction and the amount of bullet obturation into the rifling.
The less deformation and friction the faster the bullet goes for the same amount of pressure.

Cheers.

 

[Darryle]

Found this post by Frank Green from Bartlein discussing number of grooves, accuracy and bullet failure:

Re: 5R or 6 groove barrel

For the most part there is no accuracy difference with the number of grooves.

I don't believe a 5R the bullets seal better and you get more velocity as some claim.

What I do believe in is that the 5R (odd number of grooves) and the gentler angle on the sides of the lands help with distorting the bullet jacket less and this helps with bullet failure. Especially with some of the thin style match jacket bullets. Bullet failure is more of a problem for a long range shooter than a short range shooter.

The way I clean my guns I don't see a difference in cleaning between a 5R and conventional style rifling.

A 6mm caliber barrel and shooting light weight shorter jacket bullets like 70gr. etc....don't like the 5R style rifling. They will shoot around 1/3 moa but no better. On the short light weight 6mm bullets go with conventional style rifling. I don't care if it's a 4 groove, standard 5 groove etc....they will shoot better. If shooting a 6mm barrel and shooting the 100gr. and heavier bullets go with the 5R. Again no accuracy difference there just with the light bullets.

Later, Frank
Bartlein Barrels

 

[338 dude]

Found this post by Frank Green from Bartlein discussing number of grooves, accuracy and bullet failure:

Sounds like good advice from a trusted source to me

 

[Tiny Tim]

Gonna show my ignorance on the subject here. Are the lands on a 3, 4, 5, and 6 groove al the same relative width? Is that how they reduce friction? Is it simply that the grooves are wider?

 

[milo-2]

Gonna show my ignorance on the subject here. Are the lands on a 3, 4, 5, and 6 groove al the same relative width? Is that how they reduce friction? Is it simply that the grooves are wider?

On say a 3 groove, the rifling or lands would be wider, not the grooves. So there would be more bullet to actual surface bore dia contact.
My experience with 3 groove barrels are the opposite of the above posters, they were quite a bit slower, not that anything was was equal in how I came to my determination.

 

[milo-2]

Interesting subject, more groves more spin = less fps or just more groves = more accuaracy??

Would be good to see some side by side comparisons with the same loads!

Twist rate is just that, not sure how the number of grooves would make a bullet spin faster.

 

[milo-2]

Found this post by Frank Green from Bartlein discussing number of grooves, accuracy and bullet failure:

I am not here to disrupt a discussion, but right now, my newest barrel, a Bartlein 6mm gain twist, 7.7-7tw, is looking like it may be the most accurate barrel I have ever shot. One would think a gain twist is disrupting jacket the whole way down the barrel, deforming jacket more than normal.
Now whether I am qualified, or better yet equipped to make that claim may be questionable as there are a lot of variables that need to be factored in.

 

[elkaholic]

Lands can be different widths and contours depending on manufacturer. For example, A 5r Rock lands are narrower than most others and they often produce more velocity.The amount of friction produced is determined, at least in part, by total surface area of the lands, so it isnt just a matter of number of lands. Three groovers like Lilja have wider lands, but not necessarily more total surface than a barrel with more lands.
The 3 groovers tend to have a little slower throat eroision because the wider lands erode a slower rate.
5c Broughtons were known to be fast barrels
with their canted land design. I hope someone continues manufacturing them since they have recently gone out of business. The amount of polishing and bore tightness and consistency also affect speed so just comparing lands to speed isnt always the last word either.

 

[gillettehunter]

Broz has some interesting thoughts on some 3-4 groove barrels here:

Effects of 3 and 4 Groove Barrels on thin Jacketed Bullets

OK, much of this is related to what I have seen first hand and how we were able to fix some problems. The rest is from some research I have done over the years. It started years and years ago with reports of some jacketed bullets "blowing up" on impact with little to no penetration. Back then...

www.longrangeonly.com

Read and decide if it applies in any way shape or form to what your doing.
Bruce

 

[elkaholic]

Broz has some interesting thoughts on some 3-4 groove barrels here:

Effects of 3 and 4 Groove Barrels on thin Jacketed Bullets

OK, much of this is related to what I have seen first hand and how we were able to fix some problems. The rest is from some research I have done over the years. It started years and years ago with reports of some jacketed bullets "blowing up" on impact with little to no penetration. Back then...

www.longrangeonly.com

Read and decide if it applies in any way shape or form to what your doing.
Bruce

I agree with his post.

 

[David Emerson]

I have a 24" 3r groove 6.5 manbun that shoots 50-75fps faster than the same length 5r groove barrel. I recall at the time I ordered this barrel that 3 groove barrels were advertised as an easy way to pick up velocity. The Labradar appears to back that up with the various factory ammo I have used.

Now that I am in the process of building either a 270 or 7MM WSM, I am wondering if that same thought applies to magnum calibers with respect to the faster twist rates used these days? Does bore diameter have any effect?

I am also wondering if barrel longevity is affected by the number of grooves? Less grooves equals faster erosion?

Just trying to gain more knowledge on barrel characteristics, so I appreciate you sharing your knowledge with me.

Found this post talking about more grooves helping bullets remain intact, th I do not know about particular groove count adding velocity. I had a 243 catbird 8 twist 3 groove lilja that would blow 105 amax. The jackets were too thin. 107 sierra no problem. I know with the lilja the lands in a 3 groove are twice as wide as the 6 groove. Dan says they last about 20% longer. Same land to groove ratio but with 3 they are double the size. And I have never had one that did not shoot very well. But it makes sense they are harder on thin jacket bullets. I know the navy only wants 4 groove barrels. Must have something to do with the bullets they use.