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Rifle barrels, how many grooves?

captjm

Plastic
Joined
Jan 23, 2009
Location
Temecula, CA USA
Maybe this is not the proper forum for this question and if so I will apologize now. With all the choices on rifle barrels, materials and rifling processes out today I am wondering if there has been any research done on how many grooves is sufficient to stabilize the bullet? The fewest amount required would be my guess but what is that number and would it very according to barrel diamater and twist rate? A close up photo of a tank barrel shows too may lands to count. Springfield 03 rifle barrels were available with two groves.
What would be the ideal number for 338 Lapua with a 28 inch 10 twist barrel shooting the 300 grain Sierra matchking? Opinions are ok!
 
I have read that there was little practical difference in accuracy between the two groove and four groove 03A3 barrels.
 
rifle grooves

Hello, give Pac-Nor barrel company a call. They are in Oregon last I knew. They offer groove options and have a great product. I bought a few barrels from them with different groove and twist rates. Cheers, Alan
 
The number of grooves doesn't affect stability, only the twist rate does. The number of grooves and depth of grooves affects drag, blowby, and tendancy to foul. For something different, take a look at polygonal rifling. No grooves. According to an associate of mine who worked with the development of that in Germany, polygonal rifling reduced blowby 40%, while increasing velocity 10% during their tests. It can only be used with jacketed bullets though. Pac-Nor used to offer them. I think the Marlin microgrooves work in a similar way. I don't think they're very sharp, which reduces fouling. They work good in my experience. Love my Marlin 60!
 
I gather that 3 groove barrels are in presently fashion for 1,000 and 1,200 yard shooting. From what I can make out, the bigger lands are supposed to be better at resisting erosion from the big loads of slow burning powder used.

Lots of small lands are supposed to be able to give the same contact area for spinning the bullet (rather than it skidding down the bore) but with less distortion of the bullet and less likelyhood of giving you little fins on the bullet base.

With big military stuff, the projectiles often have just one or two short gliding metal bands to take the rifling, so they probably need lots of lands to grip the bands rather than putting say three 1/2" slots in them.

Again with big military stuff, you have sufficient room in the rifling head for some complex multiple cutters to form lots of grooves. I'm assuming that the smaller, 20mm and 30mm and simmiller are cold forged over carbide mandrels now? so large numbers of grooves and fancy forms of rifling becomes much less expensive to achieve.

Lindsay reprinted a small booklet of ordnance articles from 1880 or 1890, in that there are descriptions of rifling big guns with both gain twist AND with grooves that became shallower towards the muzzel (the pull rod for the rifling head was a tube, and an inner rod controled the protrusion of the cutter this was turned by a pin running in a helical track).

Addition:
The US traditionally seemed to favour even numbers of groove (easy to mike), while the Brits seemed to prefer odd numbers (pita to mike) which allowed the rifling head to be supported by a land opposite the cutter.
 
Odd Number Grooves

An odd number of lands and grooves is supposedly more accurate with an open based FMJ bullet. The theory being that the bullet is not squeezed as much between two lands, so less lead is pushed out of the base of the bullet affecting the accuracy. This is why the M24 has a 5 groove barrel to shoot FMJ bullets.
 
Number of grooves is apparently not very important. The width of the lands definitely would affect how long they last although the only place they wear significantly is in the throat where the heat from the powder burn is greatest. If you want to experiment, try a gain twist from zero for a few inches in front of the chamber to whatever you need for stabilization at the muzzle.

The logic here is that you don't want to engage the rifling with the bullet at speed or it will skid before taking up the spin. With straight rifling to begin with, you can ramp up the spin with the bullet already in the grip of the rifling.
 
If you want to experiment, try a gain twist from zero for a few inches in front of the chamber to whatever you need for stabilization at the muzzle.

Only one issue with this. If the grooves in the bullet start out straight (0 twist) and then the grooves change to angled grooves (say 1 turn in 10" for a 200 gr .30 cal) the grooves will end up tapered in the bullet (wider at the back of the bullet) and stability will suffer. Gain twists were popular with patched balls and soft lead bullets, but the amount of gain twist is minimal (ie from 1-30 to 1-26 twist). The lead or patch deformed enough to follow the rifling. Variations in twist rate up OR down over about 3/4" have been PROVEN detrimental to accuracy in benchrest barrels. That is why some benchrest shooters have a barrel scan done before wasting money threading and chambering to ensure consistent rifling.

BTW, Pac/Nor is in Brookings, OR (about 3 hours drive from my shop), and I have one of their polygon rifled stainless match barrels on my scratch-built 6ppc bolt action. I picked 1-10 twist so I could shoot heavier bullets for deer hunting (std for the PPC is 1-14 for 68 gr boat-tails). I have developed loads with H322 for 55gr Ballistic Tips, 70gr BTs, 90gr BTs and 95gr Partitions that ALL shoot consistently under 1/2" at 100 yds. One barrel doesn't prove anything positively, but if your twist is fast enough for your heaviest bullet, and the chamber work is perfect, generally accuracy will be at least varmint/ hunting good, but not benchrest good with all bullet weights. This combo has accounted for 2 3pt bucks, 2 does, a few rock chucks and innumerable sage rats. No deer has needed a 2nd shot with the Partitions, and the diggers positively EXPLODE with the 55gr ballistic tips.:D
Back on topic though, Pac/Nor's polygon barrels actually still have lands and grooves, but instead of sharp 90degree corners, the lands have angled sides. This does allow a little more velocity with lower engaving pressure, but you must help your cleaning rod follow the twist when you clean or the patch will just cruise straight down the barrel without turning:nutter:. Copper fouling is greatly reduced, though, as it tends to accumulate in the corners of conventional rifling. I have been pleased with this setup, and will probably replace it with the same when it wears out. As for number of grooves some cartridges seem to be picky, some don't. The .300 WSM was proven in early tests to strongly prefer 4 or 5 grooves to 6. The .30/06 seems to perform about the same from 2 grooves to 6. Your best bet is to talk to the guys making the barrels as they get LOTS of feedback if a particular twist or groove count is not working in a particular caliber. Google Pac/Nor for a phone number and Penney will put you through to whoever has the most experience in your caliber. Do them a favor, though and if they give you the info you need, ORDER ONE OF THEIR BARRELS. I am not affiliated with them other than as a customer, but there is nothing I hate worse as a business owner than someone who calls and picks my brain for an hour and then buys a gun at Whale-mart because it is 20 bucks cheaper:angry::angry:
Hope this helps!
Tom
 
The purpose of the experiment would be to see if the life of the barrel would be prolonged due to the rifling remaining intact as throat erosion proceeded, which is the normal cause of loss of accuracy in barrels. The twist would be a true gain twist with no abrupt change in pitch at any point. That would completely defeat the idea. It would start with infinite pitch and increase in pitch to whatever was necessary based on the heaviest bullet to be used or the standard pitch for the caliber.

While not intended for benchrest use, if proved, the process could be used for any application that it provided sufficient accuracy for. There are many applications where .5 minute groups are more than adequate, but benchrest is not one of them (except at 1000 yards.) :-)
 
Tom,
If you will take the time to actually visit with the barrel makers you will find they produce what their customers want. Nothing has been proven that says one way is any better than others. Pac Nor makes good barrels and are good people, but they are not used by the long or short range competition shooters. If you get a good barrel, you get a good barrel.
Butch
 
Tom,
If you will take the time to actually visit with the barrel makers you will find they produce what their customers want. Nothing has been proven that says one way is any better than others. Pac Nor makes good barrels and are good people, but they are not used by the long or short range competition shooters. If you get a good barrel, you get a good barrel.
Butch

I wasn't saying that the way they make a particular barrel is the only way, indeed they offer MANY options on twist rates and rifling styles in any given caliber. I only meant to point out that the barrel makers are in touch with what the shooters are finding success with.
It is true that with any barrel maker some barrels shoot better than others, even if they are produced sequentially on the same machine with the same tooling and gauge the same. As far as competition shooters using Pac Nor barrels, I recall that several Precision Shooting writes have used their barrels (Geza Nagy comes to mind for one) and maybe it is somewhat of a regional thing, but quite a few short range (100 to 300 yds) shooters on the West coast shoot their barrels. I know the owner's son campaigns a .22/6mm Rem wildcat in competitions with some success. There are quite a few barrel makers who are capable of making a high percentage of their barrels more accurate than their owners can shoot them ( Bartlien, Kreiger, and Lilja come to mind) but even this can change over time as employees change, owners retire, Etc. Barrel makers must constantly prove they are competitive TODAY to stay at the top of the list.
Tom
 
Geza has been gone for a long time. As I said, Pac Nor hasn't been on an equip list of winners in many a year if ever.
Certainly not meaning to put you down, just need to clear the air.
Butch
 
"Gain twists were popular with patched balls and soft lead bullets, but the amount of gain twist is minimal (ie from 1-30 to 1-26 twist)."

moaprecision, if this is true, why does my S&W460Magnum have 1in100 down to 1in20 twist in a 8-3/8" barrel? It is built for jacketed rounds or lead. It holds a better group with 460 jacketed bullets, than with 45LC cowboy rounds(though they're almost the same). Younger eyes or more than 7X would probably make my 3"@75yd pattern look bad, but I believe it's the most accurate pistol I've ever shot, and it's the first one that had graduated twist.
Maybe the short distance it's graduated in makes the difference, I don't know. Just food for thought.
 
"Gain twists were popular with patched balls and soft lead bullets, but the amount of gain twist is minimal (ie from 1-30 to 1-26 twist)."
moaprecision, if this is true, why does my S&W460Magnum have 1in100 down to 1in20 twist in a 8-3/8" barrel? It is built for jacketed rounds or lead. It holds a better group with 460 jacketed bullets, than with 45LC cowboy rounds(though they're almost the same). Younger eyes or more than 7X would probably make my 3"@75yd pattern look bad, but I believe it's the most accurate pistol I've ever shot, and it's the first one that had graduated twist.
Maybe the short distance it's graduated in makes the difference, I don't know. Just food for thought.

More so than the length of the barrel, the length of the bearing area on a handgun bullet is what's important. It is much closer in profile to the old conical rifle bullets to which I was referring than a modern rifle bullet. If the length of rifling contact is much longer than the diameter of the bullet, variations in twist rate deform more of the jacket. The next time you recover a bullet at the range, look at the rifling marks on the bullet and imagine how much the angle of the rifling would have to change to go straight along the length of the bullet. Compare a .223 with a 1-7 twist and a long bullet to a .45 cal with 1-20 and a bearing area less than its diameter. Also, likely the reason the cowboy rounds don't shoot as well is the huge unsupported jump between the shorter case and the throat of the chamber:nutter:. The bullet from the .460 case is already in the throat before the base of the bullet leaves the case. One reason for the graduated twist on your .460 may be that the high velocity from full .460 loads would likely strip the rifling off the bullets (esp lead bullets) if they went from no rifling (in the cylinder and forcing cone) right into a fast twist:eek:. Colt used to be very fond of gain twist barrels in the pre SAA days, but I don't believe any of their current revolvers use it. I may be uninformed on the state of the art for revolver cartridges, my experience is mostly in precision bolt action rifles. Feel free to set me straight if I am mistaken!
Tom
 
Geza has been gone for a long time. As I said, Pac Nor hasn't been on an equip list of winners in many a year if ever.
Certainly not meaning to put you down, just need to clear the air.
Butch

I stand corrected;) I see a lot of their barrels at the local matches, but I looked back at the last few regionals, and don't see any in the winner's circle. They seem to shoot well enough to keep the local Tactical type rifle shooters happy (my rifles generally average 1/4 to 1/2 MOA in the larger calibers they prefer). I haven't shot competitively in a while (too busy:D), so I guess I'm the one out of touch!
Tom
 
I find 5 groove barrels takes me much longer to indicate then the 4 groove. The 4 groove, when timed with the chuck jaws, or 6 groove in a 6 jaw is a lot less frustrating to get dialed right in.

I have had very good luck with 4 groove kriegers and 5 groove Broughton canted land barrels. I've chambered a 6 groove Shilen that shoots hole over also. I will note that # of grooves is about the last concern I have, except in terms of planning my time to fine indicate. (<.0003 TIR goal)

Ben
 
"my experience is mostly in precision bolt action rifles. Feel free to set me straight if I am mistaken!
Tom"

I believe you're right, and I hadn't considered bullet contact length. The 460 was only graduated so lead bullets could also be used, if my memory serves me right. It certainly doesn't hurt the short contact area of a 200gr .452 bullet. Probably best it is graduated even for copper jacketed @2300fps, might strip that too.
 
The number of grooves doesn't affect stability, only the twist rate does. The number of grooves and depth of grooves affects drag, blowby, and tendancy to foul. For something different, take a look at polygonal rifling. No grooves. According to an associate of mine who worked with the development of that in Germany, polygonal rifling reduced blowby 40%, while increasing velocity 10% during their tests. It can only be used with jacketed bullets though. Pac-Nor used to offer them. I think the Marlin microgrooves work in a similar way. I don't think they're very sharp, which reduces fouling. They work good in my experience. Love my Marlin 60!

Polygonal rifling wasn't invented in Germany, nor was it invented recently, Joseph Whitworth first made cannons with it then later he made rifles with it, many of which found their way to America. Many other people, other than HK, have played with it too.
 








 
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