Which Twist for a 9.3X64?

29 January 2012, 18:13

Ray,

quote:
Come back down to earth and get back on this thread regarding the 9.3x62 barrel twist!

I did that in my first post: "If you are building a rifle, go with the tightest twist you can get."

quote:
I'm not picking at you. I posted that info above to help so we could have some FACTS to discuss rather than just opinions and theories.

Your facts are based on the Greenhill method and are wrong. Not your fault, as I pointed out. My opinions and theories are based on the work of Bob McCoy and others and based on the latest information - well, at least the previous century and not the 1800s. 30 Years of designing and making bullets may also have something to do with my opinions and theories.

quote:
I'm most interested in Nolser 286 PT, the Swift 300 "A", and the Barns 286 Solid. AND am willing to listen.

To get the right numbers for the NPT and Barnes bullets, go to the links I gave or download McGyro and go to work.

quote:
Show us how the Greenhill formula would compare to the links you posted.

It would be better that you do it yourself. You do not believe what I post and, in any case, I have no interest in the bullets you want to use. I would use something else (but of course I am wildly biased).

29 January 2012, 19:16

ALF

It's a wonder the 9.3x62 in it's original, " stock--out the box- slow twist rate" and the 9.3 x64 ever got to kill anything ?

Perhaps they, and those who owned and hunted with them never got the memo ? They need fast twist barrels and super bullets to make em work?

So if there is anyone out there with a 1:14 9.3x62 or 9.3x64 please let me know I will gladly take them off your hands, especially if it's a old Mauser or better yet and genuine long octagonal barrelled Brennecke

29 January 2012, 20:33

Gerard

That is as hackneyed a statement as "you can load it again", "during which part of the animal's death did the bullet fail" and "animals don't read tables". Come on Alf, don't play dumb.

29 January 2012, 21:00

RaySendero

Ok Gerard,

Let's try this again. Don't put words in my mouth - I never said I disagreed with anything. Even offered to truly listen if you would show us the difference between the various formulas you linked.

Whether you recognize it or not - You come across as just "lobbing shots over the bow" but provide no substance and deflect reasonable requests. All I asked was that you demonstrate your knowledge of both formulas and provide an example showing that there is a practical difference for picking a 9.3 barrel twist so that we could come away with some new knowledge from this thread.

So far you seem like a child that has found a new toy and wants to show it everyone but really does know how it works, much less explain it to others.

29 January 2012, 21:32

Gerard

Hello Ray,

quote:
show us the difference between the various formulas you linked.

Classic Greenhill:

T' = 150 / L'

Modified Greenhill:

T = 150 * D^2 / L

Bowman:

T = 3.5 * V^0.5 * D^2 / L

Since then Don Miller has done variants of the modified Greenhill such as the Miller formula below:

Sg=(30*C5)/((C7/C4)^2*C4^3*C6/C4*(1+(C6/C4)^2))*(C8/2800)^(1/3)*((C9+460)/(59+460)*29.92/C10)

All of these are inadequate. An entry level system to use is McGyro or one of the calculators at JBM Ballistics or Border Barrels. Both are based on McGyro below.

McGyro:

10 REM MCGYRO, APRIL 1986, BY R. L. MCCOY.
20 REM ESTIMATE OF GYROSCOPIC STABILITY FACTOR (SG)
30 REM FOR A UNIFORM DENSITY PROJECTILE. USES THE
40 REM MCDRAG INPUT FORMAT, WITH TWO ADDITIONAL QUANTITIES;
50 REM PROJECTILE DENSITY (GRAMS/CC), AND RIFLING TWIST
60 REM RATE (CALIBERS/TURN). OUTPUT IS ECHO OF INPUT
70 REM FOLLOWED BY A TABLE OF LAUNCH MACH NUMBER, LAUNCH
80 REM GYROSCOPIC STABILITY FACTOR, AND RIFLING TWIST RATE
90 REM REQUIRED TO GIVE SG=1.5 (SLOWEST ACCEPTABLE TWIST RATE).
100 REM
110 REM THE STANDARD DEVIATION OF THE SG ESTIMATE IS
120 REM 5 PERCENT AT SUBSONIC AND SUPERSONIC SPEEDS, AND
130 REM 10 PERCENT AT TRANSONIC SPEEDS.
150 CLS
160 KEY OFF
170 COLOR 7, 1, 8: CLS
180 KEY ON
190 DIM M(22), N15(22), S6(22)
200 REM
210 REM define table of launch mach numbers
220 REM
230 DATA 0.5,0.6,0.7,0.8,0.9,0.95
240 DATA 1.0,1.1,1.2,1.3,1.4,1.5
250 DATA 1.6,1.7,1.8,2.0,2.2,2.5
260 DATA 3.0,3.5,4.0,5.0
270 FOR I = 1 TO 22
280 READ M(I)
290 NEXT I
300 RESTORE
310 REM input projectile dimensions
320 CLS
330 PRINT "Enter the McGyro Inputs, one quantity at a time."
340 PRINT
350 PRINT "Enter projectile reference diameter (mm):";
360 INPUT D1
370 PRINT
380 PRINT "Enter projectile total length (Calibers):";
390 INPUT L1
400 PRINT
410 PRINT "Enter nose length (Calibers):";
420 INPUT L2
430 PRINT
440 PRINT "Enter RT/R (Headshape parameter):";
450 INPUT R1
460 PRINT
470 PRINT "Enter boattail length (Calibers):";
480 INPUT L3
490 PRINT
500 PRINT "Enter base diameter (Calibers):";
510 INPUT D2
520 PRINT
530 PRINT "Enter meplat diameter (Calibers):";
540 INPUT D3
550 PRINT
560 PRINT "[NOTE: Do not enter the center of gravity"
570 PRINT "location. Program assumes the center"
580 PRINT "of gravity is at the volume centroid]"
590 PRINT
600 PRINT "Enter projectile density (grams/cc):";
610 INPUT R10
620 PRINT
630 PRINT "Enter rifling twist rate (Calibers/turn):";
640 INPUT N
650 PRINT
660 PRINT "Enter projectile identification:";
670 INPUT K$
680 PRINT
690 CLS
700 PRINT "McGyro, April 1986, R. L. McCoy."
710 PRINT
720 REM echo input data
730 PRINT "Projectile Identification: "; K$
740 PRINT
750 PRINT "DREF", "LT", "LN", "RT/R"
760 PRINT "(MM)", "(CAL)", "(CAL)"
770 PRINT D1, L1, L2, R1
780 PRINT
790 PRINT "LBT", "DB", "DM", "RHOB", "TWIST"
800 PRINT "(CAL)", "(CAL)", "(CAL)"; "(GM/CC)", "(CAL/TURN)"
810 PRINT L3, D2, D3, R10, N
820 PRINT
830 PRINT " LAUNCH", "LAUNCH", " N"
840 PRINT "MACH NO."; SG; ","; (SG = 1.5); ""
850 PRINT
860 S1 = SQR(1 - D3)
870 S2 = 1 - D2 ^ 2
880 FOR I = 1 TO 22
890 IF M(I) <= .95 THEN 930
900 IF M(I) >= 1.1 THEN 950
910 G1 = 71.73001 - 42.433 * M(I)
920 GOTO 960
930 G1 = 20.082 + 3.726 * (M(I) / SQR(1 - M(I) ^ 2))
940 GOTO 960
950 G1 = 35.079 - 24.066 * (SQR(M(I) ^ 2 - 1) / M(I))
960 A1 = G1 * S2
970 IF M(I) < 1 THEN 990
980 IF M(I) >= 1 THEN 1030
990 B1 = SQR(1 - M(I) ^ 2)
1000 B = .82112 + .36971 * B1
1010 A = 34.779 + (24.091 + (8.977 - 12.804 * R1 + 8.38 * R1 ^ 2) * L2) * S1 * B1 - A1
1020 GOTO 1060
1030 B1 = SQR(M(I) ^ 2 - 1) / M(I)
1040 B = 1.0528 + .23379 * B1 - .004884 * (M(I) - 1)
1050 A = 58.873 + (8.115 + (14.15 - 15.348 * R1 + 7.216 * R1 ^ 2) * L2) * S1 * B1 ^ 2 - A1
1060 N15(I) = (A * SQR(R10)) / (L1 ^ B)
1070 S6(I) = 1.5 * ((N15(I)) / N) ^ 2
1080 NEXT I
1090 REM Print McGyro Output
1100 U$ = " #.## ##.## ###.##"
1110 FOR I = 1 TO 22
1120 PRINT USING U$; M(I); S6(I); N15(I)
1130 NEXT I
1140 PRINT
1150 PRINT
1160 PRINT "Copy this? (Enter Y for Yes, N for No):";
1170 INPUT K2$
1180 IF K2$ = "N" THEN 1410
1190 LPRINT
1200 LPRINT
1210 LPRINT "McGryo, April 1986, R. L. McCoy."
1220 LPRINT
1230 LPRINT "PROJECTILE IDENTIFICATION: "; K$
1240 LPRINT
1250 LPRINT "DREF", "LT", "LN", "RT/R"
1260 LPRINT "(MM)", "(CAL)", "(CAL)"
1270 LPRINT D1, L1, L2, R1
1280 LPRINT
1290 LPRINT "LBT", "DB", "DM", "RHOB", "TWIST"
1300 LPRINT "(CAL)", "(CAL)", "(CAL)", "(GM/CC)", "(CAL/TURN)"
1310 LPRINT L3, D2, D3, R10, N
1320 LPRINT
1330 LPRINT "MACH NO.", " SG", "(SG=1.5)"
1350 LPRINT
1360 FOR I = 1 TO 22
1370 LPRINT USING U$; M(I); S6(I); N15(I)
1380 NEXT I
1390 LPRINT
1400 LPRINT
1410 REM CHECK FOR ANOTHER CASE
1420 PRINT
1430 PRINT
1440 PRINT "Run another case"
1450 PRINT "Enter Y for Yes, N for No:";
1460 INPUT K1$
1470 IF K1$ = "Y" THEN 310
1480 END

New toy. That is funny. See this post dating back six years.

29 January 2012, 21:55

RaySendero

quote:
Originally posted by Gerard:
Hello Ray,
quote:
show us the difference between the various formulas you linked.

Classic Greenhill:

T' = 150 / L'

Modified Greenhill:

T = 150 * D^2 / L

Bowman:

T = 3.5 * V^0.5 * D^2 / L

Since then Don Miller has done variants of the modified Greenhill such as the Miller formula below:

Sg=(30*C5)/((C7/C4)^2*C4^3*C6/C4*(1+(C6/C4)^2))*(C8/2800)^(1/3)*((C9+460)/(59+460)*29.92/C10)

All of these are inadequate. An entry level system to use is McGyro or one of the calculators at JBM Ballistics or Border Barrels. Both are based on McGyro below.

McGyro:

10 REM MCGYRO, APRIL 1986, BY R. L. MCCOY.
20 REM ESTIMATE OF GYROSCOPIC STABILITY FACTOR (SG)
30 REM FOR A UNIFORM DENSITY PROJECTILE. USES THE
40 REM MCDRAG INPUT FORMAT, WITH TWO ADDITIONAL QUANTITIES;
50 REM PROJECTILE DENSITY (GRAMS/CC), AND RIFLING TWIST
60 REM RATE (CALIBERS/TURN). OUTPUT IS ECHO OF INPUT
70 REM FOLLOWED BY A TABLE OF LAUNCH MACH NUMBER, LAUNCH
80 REM GYROSCOPIC STABILITY FACTOR, AND RIFLING TWIST RATE
90 REM REQUIRED TO GIVE SG=1.5 (SLOWEST ACCEPTABLE TWIST RATE).
100 REM
110 REM THE STANDARD DEVIATION OF THE SG ESTIMATE IS
120 REM 5 PERCENT AT SUBSONIC AND SUPERSONIC SPEEDS, AND
130 REM 10 PERCENT AT TRANSONIC SPEEDS.
150 CLS
160 KEY OFF
170 COLOR 7, 1, 8: CLS
180 KEY ON
190 DIM M(22), N15(22), S6(22)
200 REM
210 REM define table of launch mach numbers
220 REM
230 DATA 0.5,0.6,0.7,0.8,0.9,0.95
240 DATA 1.0,1.1,1.2,1.3,1.4,1.5
250 DATA 1.6,1.7,1.8,2.0,2.2,2.5
260 DATA 3.0,3.5,4.0,5.0
270 FOR I = 1 TO 22
280 READ M(I)
290 NEXT I
300 RESTORE
310 REM input projectile dimensions
320 CLS
330 PRINT "Enter the McGyro Inputs, one quantity at a time."
340 PRINT
350 PRINT "Enter projectile reference diameter (mm):";
360 INPUT D1
370 PRINT
380 PRINT "Enter projectile total length (Calibers):";
390 INPUT L1
400 PRINT
410 PRINT "Enter nose length (Calibers):";
420 INPUT L2
430 PRINT
440 PRINT "Enter RT/R (Headshape parameter):";
450 INPUT R1
460 PRINT
470 PRINT "Enter boattail length (Calibers):";
480 INPUT L3
490 PRINT
500 PRINT "Enter base diameter (Calibers):";
510 INPUT D2
520 PRINT
530 PRINT "Enter meplat diameter (Calibers):";
540 INPUT D3
550 PRINT
560 PRINT "[NOTE: Do not enter the center of gravity"
570 PRINT "location. Program assumes the center"
580 PRINT "of gravity is at the volume centroid]"
590 PRINT
600 PRINT "Enter projectile density (grams/cc):";
610 INPUT R10
620 PRINT
630 PRINT "Enter rifling twist rate (Calibers/turn):";
640 INPUT N
650 PRINT
660 PRINT "Enter projectile identification:";
670 INPUT K$
680 PRINT
690 CLS
700 PRINT "McGyro, April 1986, R. L. McCoy."
710 PRINT
720 REM echo input data
730 PRINT "Projectile Identification: "; K$
740 PRINT
750 PRINT "DREF", "LT", "LN", "RT/R"
760 PRINT "(MM)", "(CAL)", "(CAL)"
770 PRINT D1, L1, L2, R1
780 PRINT
790 PRINT "LBT", "DB", "DM", "RHOB", "TWIST"
800 PRINT "(CAL)", "(CAL)", "(CAL)"; "(GM/CC)", "(CAL/TURN)"
810 PRINT L3, D2, D3, R10, N
820 PRINT
830 PRINT " LAUNCH", "LAUNCH", " N"
840 PRINT "MACH NO."; SG; ","; (SG = 1.5); ""
850 PRINT
860 S1 = SQR(1 - D3)
870 S2 = 1 - D2 ^ 2
880 FOR I = 1 TO 22
890 IF M(I) <= .95 THEN 930
900 IF M(I) >= 1.1 THEN 950
910 G1 = 71.73001 - 42.433 * M(I)
920 GOTO 960
930 G1 = 20.082 + 3.726 * (M(I) / SQR(1 - M(I) ^ 2))
940 GOTO 960
950 G1 = 35.079 - 24.066 * (SQR(M(I) ^ 2 - 1) / M(I))
960 A1 = G1 * S2
970 IF M(I) < 1 THEN 990
980 IF M(I) >= 1 THEN 1030
990 B1 = SQR(1 - M(I) ^ 2)
1000 B = .82112 + .36971 * B1
1010 A = 34.779 + (24.091 + (8.977 - 12.804 * R1 + 8.38 * R1 ^ 2) * L2) * S1 * B1 - A1
1020 GOTO 1060
1030 B1 = SQR(M(I) ^ 2 - 1) / M(I)
1040 B = 1.0528 + .23379 * B1 - .004884 * (M(I) - 1)
1050 A = 58.873 + (8.115 + (14.15 - 15.348 * R1 + 7.216 * R1 ^ 2) * L2) * S1 * B1 ^ 2 - A1
1060 N15(I) = (A * SQR(R10)) / (L1 ^ B)
1070 S6(I) = 1.5 * ((N15(I)) / N) ^ 2
1080 NEXT I
1090 REM Print McGyro Output
1100 U$ = " #.## ##.## ###.##"
1110 FOR I = 1 TO 22
1120 PRINT USING U$; M(I); S6(I); N15(I)
1130 NEXT I
1140 PRINT
1150 PRINT
1160 PRINT "Copy this? (Enter Y for Yes, N for No):";
1170 INPUT K2$
1180 IF K2$ = "N" THEN 1410
1190 LPRINT
1200 LPRINT
1210 LPRINT "McGryo, April 1986, R. L. McCoy."
1220 LPRINT
1230 LPRINT "PROJECTILE IDENTIFICATION: "; K$
1240 LPRINT
1250 LPRINT "DREF", "LT", "LN", "RT/R"
1260 LPRINT "(MM)", "(CAL)", "(CAL)"
1270 LPRINT D1, L1, L2, R1
1280 LPRINT
1290 LPRINT "LBT", "DB", "DM", "RHOB", "TWIST"
1300 LPRINT "(CAL)", "(CAL)", "(CAL)", "(GM/CC)", "(CAL/TURN)"
1310 LPRINT L3, D2, D3, R10, N
1320 LPRINT
1330 LPRINT "MACH NO.", " SG", "(SG=1.5)"
1350 LPRINT
1360 FOR I = 1 TO 22
1370 LPRINT USING U$; M(I); S6(I); N15(I)
1380 NEXT I
1390 LPRINT
1400 LPRINT
1410 REM CHECK FOR ANOTHER CASE
1420 PRINT
1430 PRINT
1440 PRINT "Run another case"
1450 PRINT "Enter Y for Yes, N for No:";
1460 INPUT K1$
1470 IF K1$ = "Y" THEN 310
1480 END

New toy. That is funny. See this post dating back six years.

LOL - If that's how you explain it, I now understand why you’re so frustrated.

30 January 2012, 00:16

Alberta Canuck

"[/QUOTE]It is not an argument or a debatable matter, it is fact, proven many times over. [/QUOTE]

Sure, and for centuries it was a proved fact that the sun, moon, and planets revolved around the earth.

Mathematical formulae existed which could predict the movements of all of them, usually with great accuracy.

The only problem was, the formulae had all been developed to deal with movements based on a false asumption. So every time the predictions didn't work, another "sub-formula" had to be developed and added to the mix, until the whole matter was so complex as to be in some ways useless. It confused, rather than simplified understanding.

The same MAY be occuring in the field of ballistics, especially by those who criticize Greenhill's work.

That is exactly why I didn't want to debate this with you or anyone else who has a "bought into" mind set about it, now or ever, as I said earlier.

To go farther can test our most basic physics and associated ballistic assumptions.

Your statement about static stability shows you believe the important thing is spin related to distance travelled. That may be useful for relatively crude calculations, but it may be an incorrect assumption. For one thing, it shows bullets becoming more stable as they travel farther, but "more stable" only in terms of more revolutions per foot or other unit of distance travelled.

Viewed from another perspective, the important thing may be the rate of spin per unit of time, and in that sense, stability decreases as flight time increases and spin decreases.

To really get into it, we would have to go into subnanophysics, and this is not the place to do that.

Why subnanophysics?....because the farther we go in that field, the more we realize that mass and energy are two ways of looking at the same thing.

Einstein was one of the first who realized that mass, energy, AND TIME may be THREE ways of looking at the same thing....that is, three facets of the same thing.

And in there lies the reasons a "rotation relative to time" computation may be a simpler (better?)way to look at bullet stability than just postulating a spin vs. distance approach.

No one here wants to see us get into that. Especially not me, as it is hard to discuss things open mindedly when any one of the researchers is already a "true believer" in the status quo of science.

So I will end my part in the theoretical aspect of this.

As to twist rate for rhe 9.3x64, I would choose a 1-in-11" twist if that was available. As I don't think it is handily available, I'd go with a 1-in-12" twist.