Two groove vs. Four Groove

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  • Last Post 09 March 2018
John Alexander posted this 07 March 2018

In 1957 when new condition O3A3 Springfields were $15 from the DCM a hot topic by CB shooters was whether the 2 groove barrels would shoot cast bullets better than 4 groove barrels.  Those favoring the 2 groove (Which if I remember right included Col. Harrison.) said that because the 2 groove had much of the circumence of the bore at bore diameter, that gave more support to the nose of bore riding bullets and improved accuracy. This always sounded logical to me but of course logic without testing to back it up means nothing.  Both of my O3A3s were four groove so I couldn't test.

If we knew the answer we might be able to design a better rifling configuration for CB rifles. 

Question: Since our military shooters shoot a lot of bore riding bullets and most of them in O3A3s, what have they found out about whether that old contention that two groove Springfield barrels shoot bore riding bullets better than the four groove ones. Is there anything to it?

John

 

 

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RicinYakima posted this 07 March 2018

John, you learned to be an Oregonian real quick! Poke that stick in the rattlesnake den and twirl it around and see what comes out.

Used barrels that have been fired a few hundred times with ball ammo (especially AP); I would have to say the edge goes to the two groove.

New barrels that are of pre-WWII specifications: four groove are better.

New WWII barrels are all the same, luck of the draw of the workman.

The two grooves real advantage is that they are much more tolerant of small noses on the bore rider design, but with a fat nose, they work in either.

FWIW, Ric

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45 2.1 posted this 08 March 2018

I've had several newly arsenal rehabbed 03s and A3s, either from bring-backs or the DCM sales in the early 60's. All had WW2 barrel dates. None of them showed any evidence of firing since rehabbing. The two grooves all out shot the four grooves to a rifle. Used rifles showed the same results. I imagine it might be the other way with somebody else's loads though.

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JeffinNZ posted this 08 March 2018

Are we talking about shooting the same bullet in both barrels for comparison? A bore rider might excel in a 2 groove and Loverin in a 4 groove but not vice versa.

Cheers from New Zealand

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RicinYakima posted this 08 March 2018

Jeff, Since I shoot neither of those in matches, only 311284 and 311291, I don't know what it would do.

45 2.1, The issue is that chamber specification were changed very early (Feb. 1942?) to increase throat diameter from .309" max to .311" max and the throat was lengthen a full .100" minimum. All .30 caliber ammo was classed in four grades; 1st aircraft, 2nd machinegun, 3rd rifle and 4th training. The Springfield was view first as a trainer (except for the USMC) so that they had to work with the poorest acceptable ammo. Clark Campbell's Springfield books have a good description of what happened. After the Korean war he spent his working life as an engineer at Remington and had access to all their records from WWII.

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Ken Campbell Iowa posted this 08 March 2018

... we tried a match shilen 2 groove in 22 rimfire ... in several chambering variations .... it shot not quite good enough to win regional matches.  around 0.6 moa, need 0.5 to be in top 10.     one lone sample with factory shaped bullets.  oh, it also shot better indoors relative to ( 3,4,6 ) grooves than outdoors ..

ken

 

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John Alexander posted this 08 March 2018

Of course Jeff is right.  There is little reason to think  that a O3A3 two groove barrel would shoot a Lovern style bullet any better.  As I remember it, the argument went that the good performance of a bore rider like the 299 style in the 03A3 (some apparently went on M-1s as well) two groove is because the long nose riding on the tops of the lands aligns the bullet well by resting on the tops of the lands when chambered.

The point isn't that two grooves is better than four grooves but that A3 2 groove barrels were made with the same width of cutter as the 4 groove resulting in two huge lands in the two groove barrel providing about .6 inches of land width or about 2/3 of the circumference.  The 4 groove barrels only provide about .2 inches of land width.  Tests before adoption with ball ammo showed that accuracy was about the same for jacketed bullets.

The question is will that three fold increase in land width to guide a bore riding nose provides better accuracy for a 299 (or more extreme) style bullet?

If a style of rifling proving a higher percentage of land width (the number of grooves is probably irrelevant) gives better accuracy with bore riding CBs.  Maybe we should be trying to convince a good barrel maker to make us a few barrels for testing with very wide lands.

John

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BHyett posted this 09 March 2018

Three and five groove barrels are usually equal land and groove width. These barrels have the lands and groove directly across from each other and still seem to shot well. This supports the theory of maximizing the bore-riding nose giving greater accuracy.

Country boy from Illinois, living in the Magical Pacific Northwest

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Wineman posted this 09 March 2018

No production M1 rifles were fitted with 2-groove. There were some experimental ones and there are some that have been resurrected from demilled receivers and 03A3 barrels that may have a two groove (Santa Fe?). M1917 and M1903A3 got the 2-groove barrels as did some 7.62x51 NATO Chile Mausers (again with ex M1903A3 barrels) Not sure about M1903's though. As Ric so aptly put it a den of pit vipers. Up close and personal (300 yards) the differences are small. After that range I believe that most will agree that more grooves are more accurate. Modern barrels seem to like more rather than less. In the original 30 caliber 5-groove, they are even but they are not true 308's more like 310's if you use a V block. I see better results from my M1917 with the 0.3105's made for the 303 Brit and 7.7 Japanese (yeah right) than with 0.308 diameter of similar weight.

Dave

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lotech posted this 09 March 2018

I bought two new in-the-cosmoline 2-groove barrels thirty or more years ago. I had one installed on a Krag and the other on an '03 that had a pitted barrel. I had another 2-groove on an '03 sporter. All these barrels shot cast bullets very well.

I never did a side-by-side comparison, but I doubt these barrels were any more accurate than the 4-groove barrels on another '03 and an '03-A3.  

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45 2.1 posted this 09 March 2018

 Up close and personal (300 yards) the differences are small. After that range I believe that most will agree that more grooves are more accurate.

Dave

I've shot both with several style bullets out to 600 yards (both low and high velocity)........... Two groove won! I don't agree with untested conjecture or with conventional wisdom. Test things before relying on what everybody else has written......... sometimes it is wishful thinking.

 

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John Alexander posted this 09 March 2018

Wineman: Thanks for correcting my mistake about the M-1 and two groove barrels.

After the testing of 2 groove vs. 4 groove by Remington and Government engineers In 1942 to see if the 2 groove (which could be make quicker) would be satisfactory for military service, the recommendation was:

When the approval was received, the following rifles were designated to receive the new barrel.

  • U.S. Rifle Caliber .30 M1
  • U.S. Rifle, Caliber .30 M1903A1
  • U.S. Rifle, Caliber .30 M1903A3
  • U.S. Rifle, Caliber .30 M1917

I wonder what happened that nixed their use for the M-!?  My bet would be that some hidebound general (not an unknown type in the military) who "knew" that more grooves were just "logically" better prevented the adoption of the cheaper barrel for the M-1.  The tests showed that that the two groove raised the chamber pressure a bit, was somewhat more accurate with ball ammo, and held that accuracy for about as many rounds.  But none of these differences were considered to  interfere with satisfactory use.

John

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John Alexander posted this 09 March 2018

Wineman wrote:

"Up close and personal (300 yards) the differences are small. After that range I believe that most will agree that more grooves are more accurate. Modern barrels seem to like more rather than less."

I don't agree that more grooves are better because I don't know and have never seen a study showing this. It would just be an assumption on my part. 

But if this were true, it seems very odd that barrel manufacturers making barrels for competitive jacketed benchrest shooting haven't gone to many groove barrels as Marlin's microgroove or the early Sakos.  Instead, at least one of them is staking their reputation on three groove barrels. It is doubly odd because most of them are using button rifling which couldn't raise prices much, if any, to turn out 10 or 12 groove barrels.

John

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JeffinNZ posted this 09 March 2018

From my experience with Lee Enfield two groove barrels I am aware that they were made with proportionally deeper grooves.  This was to reduce pressure due to the bullets having significantly less area in which to engrave as 5/8 of the internal barrel area was now bore (.303) diameter for a .311-.312 bullet.  Bullet material can only displace into two deeper directions and not 4 or 5 shallower grooves.  That's why we hear of folk reporting their two groove Lee Enfield barrel is .318 in the groove etc.   With a bore riding bullet such as the 314299 this wouldn't be such an issue as so little of the bullet is groove diameter but I suspect using a jacket bullet with long bearing surfaces in such barrels could produces stresses negative to good accuracy.  Maybe two groove barrels are just as accurate BUT when matched to a suitable cast bullet only.

Cheers from New Zealand

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45 2.1 posted this 09 March 2018

I have one of those two groove Lee Enfield rifles Jeff speaks of. It is not the same set up at American two grooves (and I've shot the 03, A3 and 1917 two groove barrel rifles a lot). Accuracy wasn't that great with the Lee Enfield.

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JeffinNZ posted this 09 March 2018

You must have a bad one.  This is 50m with my .303 Pygmy.

 

Cheers from New Zealand

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45 2.1 posted this 09 March 2018

That's is not the original chamber in your rifle as I've read the genesis in your FS articles! MY rifle had a like new bore and crown otherwise I wouldn't have bought it....... could be bad HOW exactly as I'm not pouring anymore time, components and money into it without something definite? It wasn't the poorest Lee Enfield I've shot, but it was close.

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joeb33050 posted this 09 March 2018

Reading this, I think about barrels and accuracy. If you want some accuracy, use a Winchester/Remington, Savage barrel. I've screwed a lotta Savage barrels on actions, and they all shoot jbs, all .30s or > shoot cast, =/< 1", bigger with cast--smaller with jacketed.

Production factories make more accurate barrels than Pope, Peterson,  Schoyen et al ever did. And they'd be the first to agree.

 

 

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