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question about bullet length to twist ratio (Read 36748 times)

westerner Frequent Elocutionist Offline deleted posts and threads record holder. Posts: 12333 Location: Why, out West of course Joined: May 29^th, 2006	Re: question about bullet length to twist ratio Reply #45 - Dec 7^th, 2011 at 12:10am	Print Post
	400 gr, .410, 1.5, 22 twist Joe.

	A blind squirrel runs into a tree every once in a while.
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frnkeore Frequent Elocutionist Offline Posts: 7650 Location: Central Point, OR 97502 Joined: Jun 16^th, 2010	Re: question about bullet length to twist ratio Reply #46 - Dec 7^th, 2011 at 12:26am	Print Post
	hmmmmmm, I guess your just lucky, Joe. That's a awful long 400 grainer. Mine is 1.375 lg. Could it be possible that you have a little gain in your rifling? Is that rifle your Ballard? Frank

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frnkeore Frequent Elocutionist Offline Posts: 7650 Location: Central Point, OR 97502 Joined: Jun 16^th, 2010	Re: question about bullet length to twist ratio Reply #47 - Dec 7^th, 2011 at 12:34am	Print Post
	When I was trying to shoot the 1.165 lg RL bullet in my 16 twist rifle (that comes out at SG 1.197) it would group about 2.5 inches at 200 and throw a flier here and there. 4 to 5 out of 5 would always be tipped noticably. They didn't keyhole though. Frank

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westerner Frequent Elocutionist Offline deleted posts and threads record holder. Posts: 12333 Location: Why, out West of course Joined: May 29^th, 2006	Re: question about bullet length to twist ratio Reply #48 - Dec 7^th, 2011 at 12:53am	Print Post
	I miss spoke. The bullet is 1.350 long. Original Ballard and barrel. If I had to rely on one of these calculators I'd be even more screwed up, lol. Joe.

	A blind squirrel runs into a tree every once in a while.
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joeb33050 Frequent Elocutionist Offline Posts: 2613 Location: Marathon, FL Joined: Apr 20^th, 2004	Re: question about bullet length to twist ratio Reply #49 - Dec 7^th, 2011 at 5:08am	Print Post
	John, I didn't change anything. "FIRST" is the original worksheet. "FIND TWIST" calculates twist using the original Miller formula. One must enter all the data marked "ENTER", you didn't enter Sg. Try it, you'll like it. JLouis wrote on Dec 6^th, 2011 at 5:56pm: Joe here is an example: If I change the bullet length to 1.2 and the bullet weight to 215 keeping everything else the same your program tells me that I need a 12.94522606 twist. The Miller program tells me I need a 14 twist with an SG of 1.56 and as long as the SG falls between 1.4 & 2.0 the gyroscopic stability is where it needs to be. Miller, .321, 215gr., 1.2", 14" twist, 1450 fps, 59 degrees, 29.92" Sg = 1.47 You've changed something other than .321, 215, 1.2, 14. To use a 12.94522606 or to make it simple a 13 twist the SG is 1.81 of which is still fine but it might require a special barrel to be made with that twist so it over complicates things just a tad. Your program dictates the twist per say and with Millers you just type in the twist rate for the rifle on hand and you change the bullet length and weight to find the proper bullet for that particular twist and it makes life allot simpler. Nay. It ain't my formula, it's the original Miller formula found all over the net, algebra applied to solve for twist. Plug in the data, get twist. I changed nothing. Everything works correctly so far, my rearranging didn't screw up anything as far as I can see. It's algebra, not any change. J.Louis


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joeb33050 Frequent Elocutionist Offline Posts: 2613 Location: Marathon, FL Joined: Apr 20^th, 2004	Re: question about bullet length to twist ratio Reply #50 - Dec 7^th, 2011 at 5:18am	Print Post
	frnkeore wrote on Dec 6^th, 2011 at 6:27pm: For the record, it is my understanding the the Greenhill formula is, 150 X bullet dia. squared ----------------------------- = Twist Bullet length Frank; the G formula is Twist = CD^2/L * (S^/10.9)^(1/2) or, multiply what you have by the correction, which is the square root of s.g of the bullet/10.9 10.9 is the s.g. of lead. Check the net, see the correct formula. As I said, I'm looking for a picture or drawing of the standard G bullet. joe b. As I remember, the cannon formula involved either a 2 or 3 caliber ogive, also. Any other formula is not the Greenhill formula. When I started messing with bullet lengths, I found that if I used the number 175, it would solve for 1400> fps out to at least 200 yards. That is where the bullets stopped tipping and I used that formula with success until I found the DM program. We've come a long way since Greenhill, Dave Corbin has a program that deals with every aspect of stabilization, at least more that I had thought of, it includes CG, ogive and some others. I tried to use it but, it was to much work, even as a computer program. Air temp, SD and velocity DO effect bullet stabilization and over stabilization CAN effect accuracy. Such as the gyroscopic effect of the bullet trying to remain in the attitude that it was released from the barrel, creating lift on the nose when it's descending. Science and reality do intersect from time to time. Frank


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joeb33050 Frequent Elocutionist Offline Posts: 2613 Location: Marathon, FL Joined: Apr 20^th, 2004	Re: question about bullet length to twist ratio Reply #51 - Dec 7^th, 2011 at 5:25am	Print Post
	The G correction should read ((s.g./10.9)^(1/2)) so G should read T = (CD^2/L) * ((s.g./10.9)^(1/2)) C=150, D=diameter, L=length, T=twist, s.g. = specific gravity These parentheses get away from me sometimes, more often as I get older. joe b.


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joeb33050 Frequent Elocutionist Offline Posts: 2613 Location: Marathon, FL Joined: Apr 20^th, 2004	Re: question about bullet length to twist ratio Reply #52 - Dec 7^th, 2011 at 5:43am	Print Post
	In preparing the articles in the book dealing with twist, a few things became clear. The slowest twist that will stabilize the bullet at the longest range shot gives the best accuracy. Using longer bullets gives less wind deflection, requires faster twist and increases recoil. So, there is an array of twist/bullet length combinations that may be selected from, and the shooter must select his choice with the negative aspects of that choice understood. It ain't just twist and bullet length. joe b.


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joeb33050 Frequent Elocutionist Offline Posts: 2613 Location: Marathon, FL Joined: Apr 20^th, 2004	Re: question about bullet length to twist ratio Reply #53 - Dec 7^th, 2011 at 5:46am	Print Post
	Right-my problem with the DM formula is that it does not give a unique twist answer. What's that ringing? joe b. westerner wrote on Dec 6^th, 2011 at 7:11pm: Biggi and I have been messing around with the DM spread sheet. She has Excel. We can put in all sorts of different numbers to stay within SG 1.4 and SG 2. So how does one come up with the correct bullet length? All the bullets I have been using for almost thirty years in SS rifles fall within the 1.4 and 2 SG. I somehow managed this without an online twist calculator. Joe.


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John Boy Ex Member	Re: question about bullet length to twist ratio Reply #54 - Dec 7^th, 2011 at 1:13pm	Print Post
	Gentlemen - Gentlemen ... let's get back to oughtsix's original question ... Quote: If I were to order a bullet mould for a 32-30 Rem, is there a ratio for bullet length to barrel twist rate that is optimum? I have a .314 diameter barrel with a 1:24 twist. Accordingly, the original designed bullet for the 32-30 Remington was the Ideal 31356, a 125gr bullet. It is a FN 3 GG bullet. An exact look alike is the Rapine 319125, 125gr bullet with 3 GG's. Dimensions are: * 125gr * 0.319 base diameter * 0.680 length So, I plugged the dimensions into the Powley Bullet Stability Calculator using a 1:24 twist and a base at 0.316 * Calculated the Minimum Velocity = 1194 fps * Calculated the Stability Factor (SF)= 3.71 which is very maximally stabilized The minimum Twist Rate is 1:24 using these factors: SF - 3.71 Velocity - 1194 Length - 0.68 Wt - 125gr Dia - 0.316 OK oughtsix, now the deal is to find or have made the Rapine 319125 mold. If it has to be a custom mold, have the base diameter to be 0.316 - load em and shoot them ... and believe that's IT! If you want some to try - send me a PM. You'll only have to resize the bullets


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screwloosetc Ex Member	Re: question about bullet length to twist ratio Reply #55 - Dec 7^th, 2011 at 1:21pm	Print Post
	Education does not guarantee intelegence. From the very begining my formula has been slow twist for light bullets fast for heavy. Nothing to do with length. A wise man once told me the heavy bullets created an undesirable torque condition in the barrel which I am not sensitive to notice. It has also been my observation that the cast bullets performed better with the slower twists. weight and twist are a fixed condition velocity is the variable. True for both cast and jacketed. Same wise man also told me i only needed 2 powders 2400 for the straight cases 3031 for bottleneck black powder only gets the gun dirty. There now this is my opinion. Tom


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JLouis Frequent Elocutionist Offline Posts: 10625 Joined: Apr 8^th, 2009	Re: question about bullet length to twist ratio Reply #56 - Dec 7^th, 2011 at 3:12pm	Print Post
	Light bullets are shorter and heavier ones are longer so it does have to do with length. Length and weight directly relate to twist there is just no getting around it. J.Louis

	" It Is Better To Now Have Been A Has Been Than A Never Was Or A Wanna Be "
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BP Frequent Elocutionist Offline Posts: 8039 Location: Westside Joined: Aug 27^th, 2006	Re: question about bullet length to twist ratio Reply #57 - Dec 7^th, 2011 at 5:52pm	Print Post
	Joe (westerner), Frank and screwloosetc, You've provided a number of things to keep in mind. This topic reminds me of a chat I had with an aeronautical engineer who said programs and formulas are useful tools, but there is a reason we use wind tunnels, and will always need them. The results on the target, like Joe (westerner) and Frank obtained are what count. Reality will take a chunk out of theory's butt whenever it can. Remember, computer programs and their outputs gave us global warming.

	There are three kinds of men: The ones that learn by reading, the few who learn by observation, and the rest who have to pee on the electric fence and find out for themselves. Proud Noodlehead
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John Boy Ex Member	Re: question about bullet length to twist ratio Reply #58 - Dec 7^th, 2011 at 6:15pm	Print Post
	Quote: Remember, computer programs and their outputs gave us global warming. And also remember, shooters hang onto the Greenhill Formula like a starving dog hangs onto a meat bone


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BP Frequent Elocutionist Offline Posts: 8039 Location: Westside Joined: Aug 27^th, 2006	Re: question about bullet length to twist ratio Reply #59 - Dec 7^th, 2011 at 8:57pm	Print Post
	John Boy, And a whole lot of other things too!

	There are three kinds of men: The ones that learn by reading, the few who learn by observation, and the rest who have to pee on the electric fence and find out for themselves. Proud Noodlehead
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