Rifling rate of twist (Round Ball )

[wtilenw]

Almost all of us have rifled barrels, ignition systems vary. That is why I chose to post this here. I have picked up on what seems to be some " tongue-in-cheek " comments about rifling twist rate for round balls, particularly when referencing the 1-48" twist.. I understand that a fast twist is for conicals and a slow twist is for round balls so we dont have to get that basic. The person that won the 3x5 card competition was given some flak about winning with a 1-48" twist. I dont know any of you well enough to tell if this was just a joke, or if, in fact that is true. I personaly had only marginal performance with my .54's with a 1-48" twist. I now get what I would consider exceptional accuracy with a green mountain 1-70" and a lyman 1-60". Are there those of You out there that are getting target class accuracy with the 1-48" twist? I would be very interested to hear your experiences .
Idaho PRB

 

[roundball]

IMO, there's a few parts to the answer:

First, I understand and believe the ballistic theory that faster twists serve elongated projectiles better, and that slower twists serve round balls better.

Subsequently, the "middle" or "compromise" 1:48" twist gets tagged with the assumption they're pretty good for both but not outstanding for either.

Unfortunately, after being told and retold for decades the discussion tends to get reduced down to snippets or sound-bytes repeated by some people that "1:48" twists don't shoot round balls well"...when in reality, that's not the case at all.

The issue really is:
What is meant by well and for what purpose?

If you're a bullseye shooter and measure group size with a micrometer in match competition, you'll probably want every advantage you can get and use a round ball barrel.

If you're a hunter and can shoot a 2.5" groups semi-off-hand at 50-75yds with full power hunting loads in poor shooting conditions at uncertain distances out of a 1:48" barrel, it obviously shoots very well.

After finding good load combinations of powder, patch, and ball in my 1:66" round ball barrels, I've actually experimented with the same loads in my 1:48" standard barrels, caliber by caliber, and frankly, while there was a slight difference between the two sets of targets, it was not enough to write home about.

So IMO, whenever this discussion comes up, it has to be properly framed to really be of specific value:

1) Is the question a theoretical comparison between twists...if so, yes, all theory points to slower twists shooting round balls better...(but how much better?);

2) Is the question regarding a competition shooter, off the bench, using a micrometer to measure group size at fixed, known distances...if so, a round ball barrel would be preferred, if for no other reason than the theoretical answer to question #1;

3) Will round balls shoot accurately in 1:48" twists for general shooting, hunting, etc...without question the answer is yes...and put another way, I believe 1:48" twists shoot round balls more accurately than most people's shooting skills allow anyway...and 1:48" twists have been taking game for years and years.

I bought round ball barrels when I got started because I read "they shoot better"...after shooting both twists in different calibers for a number of years now, if I had to do it again, I'm not sure I'd bother buying replacement RB barrels now that I know first hand how accurate 1:48" barrels are...for me as a hunter / general purpose shooter.

 

[wtilenw]

WOW! Thanks for all that information. This is exactly what I was after.
Idaho PRB

 

[Old40Rod]

Its all the fault of some joker named Magnus.

http://www.pitching.net/mechanicsofabreakingpitch.htm#Physics

For spherical objects, the Magnus effect is directly proportional to the rate of spin. The more spin, the more effect. In theory, all other things being equal, you should do better with a 1-66 than 1-48 with roundball. This doesn't mean you will notice any difference. Like Roundball said, there are other variables that probably overcome (shot to shot/shooter to shooter) any differences in Magnus.

The nice thing about the Laws of Physics is you can't break them :master:

 

[SquirrelsaurusR]

That's why he took a ribbing for winning the shooting match with a 1:48 rifle, and yes, everyone was just joking with him. Mostly, they were just jealous because they wanted that turkey call. ::

My flint longrifle is 1:48 and shoots round balls very accurately. How accurate? I dunno, I never really bother to measure groups, as I'm not a competitive shooter. If the group on the paper is small enough to hit a deer's vital area, it's small enough for me.

Easy to please, ain't I? ::

 

[SquirrelsaurusR]

Before anyone starts giving me flak for suggesting sloppy shooting is a good thing...that was meant as a joke.

 

[Terry Zboril]

Almost all of us have rifled barrels, ignition systems vary. That is why I chose to post this here. I have picked up on what seems to be some " tongue-in-cheek " comments about rifling twist rate for round balls, particularly when referencing the 1-48" twist.. I understand that a fast twist is for conicals and a slow twist is for round balls so we dont have to get that basic. The person that won the 3x5 card competition was given some flak about winning with a 1-48" twist. I dont know any of you well enough to tell if this was just a joke, or if, in fact that is true. I personaly had only marginal performance with my .54's with a 1-48" twist. I now get what I would consider exceptional accuracy with a green mountain 1-70" and a lyman 1-60". Are there those of You out there that are getting target class accuracy with the 1-48" twist? I would be very interested to hear your experiences .
Idaho PRB

Idaho,
:imo:, As a general rule,(per caliber), fast twists will shoot well with a lighter charge, slower twists seem to like a heavier charge.

Your .54 1x48's might do well with a 50 or 60 gr. charge, for example, while the same barrel in 1x70" may need 100+ grains to group well. My .54 1x72" twist needs 115 grs of 3f to shoot 1" bench groups at 50 yds.(sometimes!)
:results:
Only range time will tell.
Regards,
Terry

 

[rayb]

How about the rifling twist formula I think it was Greenhills or something like that. ?anybody remember?


rayb

 

[Stumpkiller]

Are there those of You out there that are getting target class accuracy with the 1-48" twist? I would be very interested to hear your experiences .

50 yards offhand 1:48" .50 cal. T/C New Englander .490 PRB with 0.021" patch (castor oil moose snot lube dipped and allowed to dry several days before use). Spit damp wipe between shots and 84 gr FFg.

This after eight months of HARD trying to come up with an accurate load. I estimate I tried 40 other combinations of powder amount, patch thickness and lube before I got here. This gun was 6" at 50 yards with round ball and Bore Butter when I started. Now it's 2" at 50 yards. It has always liked Maxi-Hunters, but now I've sworn off them. :winking:

 

I had a Pedersoli Jaeger .54 with a 1 in 24 twist in a 27 inch barrel. I could bust charcoal bricketts and tootsie roll pops off a stick at a small time rondy novelty shoot. Heck, I was using 80 grains of fff. Not exactly a light load. I'm no Sam Fadala or Sgt. York but a fast twist worked for me. Dunno why or how.

 

[RussB]

How about the rifling twist formula I think it was Greenhills or something like that. ?anybody remember?
rayb

The Greenhill Formula is far from perfect, but it is still the "handiest tool" available for quick reference.
Researching the Greenhill formula you will find three constants. The original constant was 150, it was later modified for smokeless powder by using 180, then in the last few years has been revised again to meet the standards of todays muzzleloaders....or, so I'm told.

..........................................................
One of the first persons to try to develop a formula for calculating the correct rate of twist for firearms, was George Greenhill, a mathematics lecturer at Emanuel College in Cambridge, England. His formula is based on the rule that the twist required in calibers equals 150 divided by the length of the bullet in calibers. This can be simplified to:
Twist = 150 X D2/L
Where:
D = bullet diameter in inches
L= bullet length in inches
150 = a constant
This formula has limitations, but works well up to and in the vicinity of about 1,800 f.p.s. For higher velocities most ballistic experts suggest substituting 180 for 150 in the formula.
...........................................................
Using the above formula, lets work out a couple of quick "rate of twist's" for a .54 caliber round ball.

D2= Diameter .535(squared=.286225)
L= Length .535
C= Constant of 150 (original constant)
So.... D2 (diameter squared) times constant of 150 = 42.93
over, or divided by length of .535 = 80.25
Therefore; the best ROT (Rate of Twist) for the .54 caliber round ball is 1:80.25

...........................................................
If we substitute 180 as the constant for the .54 caliber round ball, we will see......
D2= Diameter .535 (squared = 0.286225)
L = Length .535
C = Constant 180 (modified constant)
So....Diameter squared x constant of 180 = 51.5205
over, or divided by length of .535 = 96.3
Therefore; The best ROT (Rate of Twist) for the .54 caliber round ball is 1:96.3
...........................................................
One can readily see the differences the constant makes. Most Black Powder shooters, as least the ones that I know, prefer to use a constant of 130 to more closely match the twist of modern rifle barrels available today.
Using a constant of 130 we see that;
D2...is the same @ 0.286225
L....is the same at .535
C....is changed to 130 (most likely best constant for ML)
So....D2 x 130 = 37.20 divided by L = 69.55
Therefore the best twist rate, using todays standard barrels, would be 1:69.55 for the .54 cal round ball.


Note; The use of the Greenhill formula is much better served when using conicals in muzzleloaders. Then you can we see why a slow twist is recommended for a RB, and a fast twist for conicals.....I personally hold more faith in the Greenhill for this purpose than any other.


Russ

 

[bob1961]

being that person that won and yes i think they were joking....my T/C hakwen 1/48" 28" barrel in .50 was the culprit....and i didn't do much with load development....pretty much just bought T/C's round balls, T/C precut and prelubed patch's in .15, and shulzthen powder for this shoot....and just powder mesurments....go fig maybe just lucky this time....was out at the range and last time and two holes covering each other by half a bullet dia and one flier 3" away on a 3x5 card at 50 yds that we use for the shoot....haven't been back out to shoot at 25 yds like the shoot in dec....can't enter but would like to see if i could tell if there was 3 holes on the card after 3 shots :crackup: ....but on a level answer i can't figure out why i get groups like i'm getting................bob

P.S....wait i know now what it was....it was the new curly maple stock i put on the gun....