4 groove vs. 6 groove barrel

[mtlucas0311]

After looking around a bit it seems that the 4 groove barrels are preferred over the 6 groove barrels, but after a search (of the title of this thread) I didn't find anything as to why the 4 groove is preferred. I just recieved the parts to build my 16" upper from WOA Wednesday and it went together nicely, but I do have a 6 groove. A little help please?

[sredish]

not an expert here but I pretty sure the 4 groove has less pressure over the 6 groove, therefore allowing the bullet to build speed more efficiently.

[Strawdawg]

http://68forums.com/forums/showthread.php?t=7220

http://68forums.com/forums/showthread.php?t=840

[DocGKR]

6.8 mm was initially developed using 5 groove barrels. Both of the "parents" of 6.8 mm have recommended 1/11 or 1/12 twists from day one. In some circles, this would be seen as a clue...

[marinesg1012]

the issue is the land to groove ration, the less friction on the bullet the less preassure which is why the 4 groove is prefered.

Doc I wish more companies would get the picture, it is looking a lot better but we still have a long ways to go.

[mtlucas0311]

ok, that makes sence. Did I read something about a certain amount of friction being desirable as it allows slower burning powders more time to build pressure? Or am I confusing something from another topic?

[constructor]

ok, that makes sence. Did I read something about a certain amount of friction being desirable as it allows slower burning powders more time to build pressure? Or am I confusing something from another topic?

With other calibers that have a more lop sided case capacity to bore area ratio that may work but the 6.8 is more efficient and uses faster powders.

[Tim_W]

Even if that were true. I would never want my barrel purposely made to have the bullets go slower so as to match some powder's burn rate. It is why they make powders with different burn rates. Or get a longer barrel then.Not to mention from lot to lot burn rates vary 5 % and can go as high as 10% Play with that in quicklaod and you woudl see its a big dif. Also no matter how much a barrel bore is polished it only take one look thru a microscope to see that the metal surface is far far from smooth. There was some very good testing done on this with chambers to see the effects on bolt thrust from highly polished chambers etc.. Only when a actually coating or lubricant was used did it create a low enough friciton co to casue a neg effect as far as bullet seal and the min friction level needed for burn rates. Its one of those things that may sound logical but when its actually tested and looked at in depth it doesn't pan out. Think about all those moly coating their bullets and bores or chrome plated which has a much tighter grain thus smoother finish than steel same with Nitrided. Not to mention that carbon itself burnishes the bore and fills microscopic space.

[mtlucas0311]

Ok, thanks for the info. I'm really happy with the way my rifle turned out, it sounds like WOA is moving toward the 4 groove barrels (from what I read on another thread) maybe my next barrel will be one of those. I have a service rifle and a match rifle from WOA, I'm sure this upper I assembled from their parts will not disappoint.

[jmarston]

I am not sure I am correct in my assumption but from some of the books I have read about internal ballistics from some
well known gun experts many of them seem to believe the pressure peek occurs from the time the bullet starts to leave
the casing to the point when it starts to engage the riflings. Then the pressure goes down from there. I am definitely no
expert but it makes sense to me. I may be true that barrels with fewer grooves have less resistance and may or may not
increase muzzle velocity compared to a typical barrel with 6 grooves. I know for sure that barrels can be incredibly accurate
with four or three grooves. My 03A3 may be even more accurate than my AR. It has four grooves and was built in 1943.