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

[Mc Fraser]

My gunsmith suggests that there is not much difference between the # of grooves. He noticed that some small caliber target bullets tend to lose their jacket mid-air when shot from a barrel that has 5-6 grooves.
I don't know much about modern military cannons, but old ones used in past world wars have lots of grooves.
My questions are towards grove-less barrels, will they shoot better, more velocity because the gas cannot escape around the bullet?
I guess it all boils down to the area of friction vs area through which the gas can escape ahead of the bullet, how that affects bullet speed and accuracy and of course the cost of manufacturing barrels.

 

[Tank308]

I saw this on this site under a 3 groove thread. It's bullet contact %.

 

[TXAoudadKlr]

From what I was told lesser groove counts can be harder on the jackets in a more extreme chambers, high velocity and high twist rate

 

[9x23w]

" I have a 24" 3r groove 6.5 manbun that shoots 50-75fps faster than the same length 5r groove barrel "

I think if you tested multiple identical barrels (same length and no. of grooves) you would see that much variation.

 

[J E Custom]

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?

The three grove has a longer throat life for the smaller calibers because of the land thickness. (Wider) so there is more land to wear off. the downside is that the three grove can be tough on some bullet jackets depending on thickness. On heavy bullets of large calibers .400 + more lands and grooves normally engrave better, so there is a land count that works best for a certain bullet diameter and weight. (There is no one land count that works best for all. the barrel manufacture will normally make a recommendation as to what land count works best based on twist rate, bullet diameter and weight.

It does to appear that the 3 grove barrels are faster if they are premium quality barrels. and I recommend them for the varmint shooter that shoots hundreds of rounds a day. but after bullets reach a certain caliber and weight, the 5 and 6 groove seam to work better. for the really big bore magnums I prefer the 8 grove barrels.

For the ultra high velocity with slow twist rates, the 3 grove works great and doesn't hurt most premium bullet jackets. But I don't recommend fast twist on this type of rifle using the 3 groove design.

Just my opinion based on experiences with different land count barrels.

J E CUSTOM

 

[MagnumManiac]

There are also equidistant grooves/lands and non-equidistant lands/grooves.
Most equidistant barrels have what is called Ballard style rifling, Kimber use this in their 4 groove barrels.
Rugers have skinny lands and wide grooves.
3 & 5 groove barrels have equidistant lands in relation to their number of grooves.
I have found barrels with skinny rifling, such as Remington & Ruger barrels are faster than those with Ballard style rifling, BUT if the number of grooves is less then there is a speed increase as well.

Clear as mud?

Cheers.

 

[bigngreen]

I try real hard not to build magnums with 3 groove barrels, the number of times I've seen them start shredding jackets on normal bullets after a few hundred rounds is ridiculous, then you end up shooting ballistic rocks to try to keep jackets together so you might as well just shoot a regular chambering with a normal bullet and barrel and save recoil and powder.
Not a fan of the three groove at all!!!

 

[MagnumManiac]

I like my 4 groove Ballard barrels and my 5R barrel. Had little chance shooting it this year, but it looks like a shooter with less than 40 rounds through it.

Cheers.

 

[skipglo]

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!

I'm thinking more grooves more drag!

 

[David Emerson]

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.

Broughtons are no longer being made?

 

[TXAoudadKlr]

Broughton 5c with canted lands sounds golden

 

[bigngreen]

Broughton 5c with canted lands sounds golden

It was!