2 versus 5 groove barrel

[w8lftr]

Is there any accuracy differance between these two? I know some studies with the 1903A3 with the two groove barrels didn't show a differance.

w8lftr

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[finloq]

Alot of debate there.
2-grooved barrels, seemed to wear faster?
Most folks will agree that 2-groove barrels prefer flat based bullets as opposed to boat tailed.
I am sure that if you are patient, some experienced blokes will chime in.

[Peter Laidler]

we did many tests and trials on the differences between the two and I wrote about it in a previous thread. Someone will resurrect it all hopefully.

[RJW NZ]

My range experience has been is that 2 groovers can have surprisingly decent accuracy, always a pleasure to find out.

[Peter Laidler]

One thing I do remember from the trials we did was that the amount of grooves was really academic because it was the pitch of the spin imparted to the bullet that gave the bullet its accuracy and not the amount of grooves. The two groovers also lasted longer but gave more friction. Absolute accuracy was a judgemental thing with a lot of variables but all in all, one was as good as the other

You can get into deep technicalities too but as I said, the two groovers were as good as the five

[Bruce_in_Oz]

If you read through comments from some of the most highly regarded barrel makers on the planet, a few common thoughts appear.

As Mr. Laidler already pointed out, the number of grooves is not the key determinant of down-range performance, but the precision and ccuracy of the manufacture of those grooves. More than 6 grooves results in very narrow lands and thus reduced throat life. Interestingly, three-groove barrels have started to appear in match-winning rifles, but there are too many variables in play once you move away from a set cartridge specification.

On the point of friction, it seems to be that if the bore and groove are polished to less than a 0.25 micro-metres (10 micro-inch) roughness, then metal fouling tends to become a problem. There seems to be a surface grade reminiscent of "lemon peel" in the .25 - .75 micro-metres range that works very well. Interestingly enough, in the electrical business, several manufacturers offer cables with outer PVC sheathing that has a “grainy” orange-peel like texture. This is designed to reduce friction and subsequent damage when cables are pulled through conduits and ducts. Note that barrels with a hard chrome lining automatically get this "orange-peel" surface due to the peculiar "clumping" and micro-fracturing of the chrome layer as it forms on the parent steel.

Conversely, of course, if the barrel is too rough, then this just acts like sandpaper on the bullet

A 5 groove barrel that bells a few thousandths of an inch at the muzzle will not shoot as consistently as a perfectly parallel 2 groove job.

A 2 groove barrel will suffer proportionally less from gas erosion at the throat than a 5 or 6 groove job, especially using cordite ammunition. Theoretically, a two groove barrel (un-plated) would have been better for "hot" applications like machine-gun barrels.

Speaking of which, if you gauge an original barrel for a a General Electric 7.62mm Minigun, the chrome-lined bore is TAPERED down towards the muzzle. This is specified on the drawings. Groove diameter seems to be constant. Given the amazing lightness of these barrels in general and especially at the muzzle, I suspect this feature is to ensure workable bore size, allowing for expansion at raised temperatures.

[charcoalburner]

I do not remember which magazine author I read this from (Charles Kershaw?) but the G&A author stated that the two groove barrels seemed to stabilize a .308 jacketed bullet in his reloads much better than the five groove barrels would. I assume he tried this due to the fact that .308 bullets were more available (at that time anyway) and came in a larger selection of weights and types. Food for thought anyway.

P.S. First time post for this newbie to the board. Thanks for the opportunity to learn more about my favorite bolt rifles.

[Badger]

Old thread discussion about this subject ...

Merits of 2 and 5 groove rifling

Regards,
Badger