i was looking on the Pac-Nor site at a barrel for a 6.5x55 project. i notice that they have several different barrels with different numbers of riflings from 3 to 6, as well as a "polygonal" (?) twist, whatever that is.... they have a 3 groove as well as a 5 groove, both with a twist of 8 and 9.

what should guide my decision as far as the number of grooves is concerned? in other words, what is the difference between a 3 groove with an 8 inch twist and a 5 groove with an 8 inch twist?

Being an ex employee of PAC-NOR, I have some experience here. The land to groove ratio is usually about 1 to 1.5, meaning the groove is a little wider than the land. Some people think it is better to have an odd number of lands and grooves so the bullet experiences less stresses when swaged into the lead. How important that is is debatable. I have had rifles shoot very well with 3 to 8 L&Gs. The poly barrels are a little hard to explain, but in a nutshell, the lands do not have steep sides going into the groove. The lands are a sort of wide trapazoid. When looking at a bore with a 90 degree borescope, it is all facets rather than distinct L&G. There is a better explanation on the Shrotmag.org site in the news section. You might need to go back a page or two. For you deciding what way to go, thnk about having less lead edges on the rifling with fewer lands. People say their 3 L&Gs clean very easy. I use them all, so I cannot say one is better than the other. I know cast bullet shooters seem to like fewer L&Gs. They are all good, and you had it right goiung to PAC-NOR. They are great and so are the barrels.

[ 12-02-2003, 07:36: Message edited by: jnrifleworks ]

From what I've been able to figure out over the years a barrel with more grooves will put more grooves into the bullet. That's it. I've not been impressed with any of the polygon barrels I've tried.
The most accurate barrels I've ever used had six lands and grooves because that's what Hart made at the time. The best long range barrel I have now has four. The bottom line is, it matters mostly in the mind of the shooter. Regards, Bill.

I copied this from Dan Lilja's site...

Q. What are the differences between 3 Groove and 6 Groove Barrels?
A. Almost all of the caliber and twist combinations in the rifle barrels we make are available with 6 lands and grooves. A few years ago we started to make barrels in a 3 groove configuration too at the request of some varmint hunters who were looking for longer barrel life. They were chambering barrels for hot 22 caliber varmint rounds and shooting the throats out of conventional 6 groove barrels fairly fast. We reasoned that if we reduced the number of grooves to 3 but kept the ratio of land to groove width the same (ie. the lands are twice as wide in a 3 groove barrel as compared to a 6 groove) that there would be more land area to resist heat erosion.

Well, it turned out that barrel life did increase and that accuracy stayed at least the equal of comparable 6 groove barrels. It is hard to put a percentage increase on barrel life but a conservative estimate might be 20%.

Benchrest shooters are always experimenting and looking for a competitive edge. Before long a few shooters, including Dan Lilja, were putting 3 groove barrels in 6PPC and 22 Waldog on their light varmint and heavy varmint class benchrest rifles. And these barrels proved to be very accurate. They started winning benchrest matches and soon became popular among the benchrest shooters. .

On the right is Dan with a .193" 200 yard group fired at a benchrest match in Billings Montana in 1998.

This was with a 6 mm PPC 13" twist 3-Groove Barrel.

And we found that as a side benefit the 3 groove barrels seemed to foul very little and clean up quickly. We attributed this to the reduced number of corners inside collecting powder and copper fouling.

This answer to 3 groove - 6 groove question is not meant to discredit the 6 groove barrels. They have consistently shoot extremely well over the years. Dan continues to shoot both 6 and 3 groove barrels on his benchrest rifles. But if you haven't tried a 3 groove you might consider one the next time you need a barrel. We do not offer them in all of our caliber and twist combinations. Our page with caliber and twist listings indicates if a 3 groove barrel is available. And we are frequently adding 3 groove buttons to our offerings. If you don't see that a 3 groove version is offered in the caliber and twist you're looking for, ask, we might soon be making it.

I have heard you get more velocity with fewer grooves, and better accuracy with more grooves.

Marlin marketed their microgroove....and maybe still do....it's all marketing hype as far as I'm concerned.

Many of the old Springfield 2-groove rifles shot very well......

The number of lands and grooves is not relevant to me...the twist rate is only relevant to the weight of bullet I want to shoot.....accuracy is dependent on many many more parameters than the number of lands and grooves.

I have a 2 groove Springfield. Bought it in 1959. It still shoots just sub-MOA. The barrel bore looks kinda weird, but it clearly gets the job done.

BTW: It really likes cast bullets. Less bullet deformation? Maybe. DB

My 03-A3 has a 2 groove barrel, and shoots wonderful groups. I too have noticed it likes cast bullets, but other than that I can tell no difference between it and a 6 groove barrel.

Good luck and good shooting,
Eterry

My only thoughts on the subject are that the less you deform a bullet as it engages the rifling the better off you are, regardless of the number of grooves. The balancing act is thus: more grooves means more opportunities to screw it up with machine marks etc. Too, more grooves allows the opportunity to use shallower rifling. I do not doubt Lilja's assertion about throat life in regards the 3 groove barrels one iota, but he builds fine barrels so why wouldn't they shoot?

The only downside to barrels with odd numbers of grooves is that computation is required to ascertain bore/groove dimensions, rather than simple measurement.