Rifling types and perfomance

[Tesoro]

I have always been curious if different quality levels of riflings can impart different levels of spin to the bullet with everything else kept constant. I know this cant be measured but could be interpolated maybe by performance on paper.
ie: could a very precise made rifling actually spin the bullet faster than a less precise one with the same twist? Can a bullet hypothetically slip over the lands as it is being spun creating different exit rpm's depending on the trueness of the bore and evenness of the lands?

The reason I ask is because I have a HS 6.5cm with 1:9 made for hunting with 120-130gr. However the guys at HS, who all shoot competitively, told me that my gun will shoot 140's lights out when I asked out of curiosity. They werent bs'ing me and I didnt go into it further at that time. But I do know they make top quality cut barrels so maybe the performance with theirs is not 'rule of thumb'. Or maybe 'rule of thumb' is exactly what it means and there are exceptions but I am a sceptic!

 

[butchlambert]

A good barrel is a good barrel. Mfg. produce what the raggedy A$$ Masses ask for as they are primarily out to make money.

 

[Stan Taylor]

Well what chambering is that 9 twist if you want good an bad answers.

 

[msinc]

The only way to know with your barrel in particular is to try it. As far as bullets slipping on the rifling and loosing twist....if you had a rifled barrel that was that bad, by the time it actually did slip over the rifling it would be shooting bad for other reasons.
I have tried them all, as far as performance {accuracy??} I cant tell any difference. If there was a difference that was quantifiable that would very quickly be the only method of rifling a barrel, because that would be the only type anyone would bother to buy. Based on what I have seen, even rifling types touted for less fouling and ease of cleaning are a fallacy.
I had a 1-in-9 twist 6.5mm barrel that did not shoot 140 grain bullets very good. It was pretty decent with 120's. I can guarantee you it was not this way because the bullet was "slipping" over the rifling. It simply didn't have enough twist. You would not see this stabilization problem at 100 yards. In fact, I suspect many barrel twist are insufficient for the bullets being used, but believed to be okay because they are not being checked at the range where it will show as a problem.
In example, the Army AMU figured out many moons ago that optimum twist for an M1A shooting 168 grain 7.62X51 was 1-in-11.25. They contracted Maremont to make a batch of match grade heavy barrels. I managed to get my hands on one of these barrels in 1987. The barrel did shoot that bullet just fine, but in windy conditions when shooters tried to use the 190 BTHP Match bullet they would tumble at 600 yards. Looked good on paper at 100, even at 200, but beyond that they started to destabilize.

 

[Alex Wheeler]

When you get to a high level of accuracy like in Benchrest you will see different styles of rifling out perform others. Even the shapes of the top of the lands and bottom of the groove withing the same style of rifling (cut vs button) seems to make a difference.

 

[butchlambert]

S

When you get to a high level of accuracy like in Benchrest you will see different styles of rifling out perform others. Even the shapes of the top of the lands and bottom of the groove withing the same style of rifling (cut vs button) seems to make a difference.

So, What is best then? We would all like to know before our next order.

 

[Alex Wheeler]

Well if your shooting LR BR with 105 class bullets a 4 groove cut will out perform a 5r cut 90% of the time. I'll tell you that much.

 

[butchlambert]

Well if your shooting LR BR with 105 class bullets a 4 groove cut will out perform a 5r cut 90% of the time. I'll tell you that much.

The 5R is a marketing tool.

 

[Alex Wheeler]

Well, go chamber a pile of each. Put them in the hands of the best shooters then give me your opinion. I bet you'll be able to form one. I read alot of "theres no difference" as the answer to so many questions. Just because you have not seen a difference does not mean others have not. I have seen a lot of data from guys that shoot smaller then me. They find things I could not because they shoot smaller. If I didnt work with those shooters I wouldnt know a lot of things. Im fortunate in that regard. I'll put it this way, if you send me a 5r cut barrel to chamber in a 6br or imp version I will call you and talk you out of it if I can. Thats how strongly I believe in the difference. In the larger bores like a 7mm or 30 I have no issues with 5r cut barrels. Theres a difference in the shape of 5r barrels as well. A rock creek is a little different looking and it will shoot the 6mm bore, Id say its the exception.

 

[butchlambert]

Alex, a good barrel is a good barrel. I know quite a few guys that shoot smaller than me. They don't all shoot the same barrel in their 6PPC or their 5.56-223 SR.

 

[Tesoro]

Well what chambering is that 9 twist if you want good an bad answers.

Its a 6.5 creed.

 

[Stan Taylor]

Its a 6.5 creed.

Honestly can't say that 9 twist will get the job done wouldn't be my preference I would rather have an 8 twist.

 

[Alex Wheeler]

Alex, a good barrel is a good barrel. I know quite a few guys that shoot smaller than me. They don't all shoot the same barrel in their 6PPC or their 5.56-223 SR.

Butch that would imply that the different bore volumes, land and groove shapes and the pressure curve changes that go along with them have no effect on the accuracy potential of a case/bullet combo. I cant agree with that, and thats not what I have seen.

 

[JBT47]

I had a 9 twist .260 Krieger. Shot nice at 1-200. Past that it would not shoot the 140’s.

 

[carlsbad]

OP's question was whether types of rifling affected bullet stability. I believe the answer is NO. Doesn't matter how many grooves you have, the spin rate of the bullet is the muzzle velocity x 12/twist rate. The bullet follows the grooves, no mater how many there are, or really bad things happen.

Use Berger's stability calculator to get some insight into what twist is needed to stabilize what bullets. But the bullet, temperature, elevation, and other atmospheric conditions matter more. --Jerry

 

[Tesoro]

Well thx. As there has never been any talk about diff rifling qualities imparting more of less rpm with the same then its probably because it is not worth talking about anymore!

I am going to put on a 22" 1:8 bbl and quit worrying about my twist. end of story.

 

[dcali]

The answer to the question you actually asked is ‘no’. The type of rifling does not change the spin. The twist rate is what determines spin. The next question is does it impact internal or external ballistics.

I don’t know about internal, but logic tells us there ought to be a small change, even if it’s just due to variation in engraving force. I think this is the source of the debate in terms of accuracy.

External ballistics have been studied in depth. There is a small, barely measurable difference in some aerodynamic coefficients between rifled and unrifled bullets. Small enough that military ballisticians ignore the effects of rifling. The differences between two types of rifling, you could safely assume matter even less.

 

[Tesoro]

Well thanks for putting the rifling myth to bed for me. As I mentioned, my 6.5cm is a lighter hunting rifle intended for the 120-130gr class. I am not sure why the HS guy told me that 140 will perform well but then I just realized he must have been referring to a 140 hunting bullet like the proven shorter Hornady interlock flat base spire point. According to my calcs 1:9 is more than adequate. If I had the choice I would prefer a 1:8 bbl and I can readily fix that with some money. But at this point I dont think shooting out to 600 with 120-123 grainers makes it seem like I am not fully taking advantage of my cartridge's capability. At 1000 thats a diff story but I dont shoot that far because I dont have a range for that.

 

[Loggins J]

Honestly can't say that 9 twist will get the job done wouldn't be my preference I would rather have an 8 twist.

I don't always agree with Stan but I agree with him on this I don't know anyone that said they shoot 140s out of a 9 twist ever one use's a 8 twist or faster

 

[Stan Taylor]

I don't always agree with Stan but I agree with him on this I don't know anyone that said they shoot 140s out of a 9 twist ever one use's a 8 twist or faster

Thanks young man