Optimum twist for a . 225 bullet .666" long

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  • Last Post 21 September 2013
Wayne S posted this 17 September 2013

 Looking for thoughts & opinions on the optimum twist for a .225 bullet  that is .666” long with a speed of 1750-1850 FPS.  It seams if you want a barrel maker or gun smith/shooter to roll his glazed over eyes back into his head just use “I want it so shoot cast bullets” and “stability programs” in a sentence . http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi this one says 1-12 ???

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LBD posted this 17 September 2013

SAECO 221?

I don't think it's that simple. I think these formulae need to account for center of gravity too, especially because of the myriad of nose configurations mold makers utilize. At least incorporating a BC would provide a useful parameter.

I started a thread a couple weeks back (IIRC) about molds for the 222Mag (1:14") and there were a couple posters who said SAECO 221 works well at higher (not sure how to quantify higher) velocities.

http://www.castbulletassoc.org/view_topic.php?id=9922&forum_id=72>http://www.castbulletassoc.org/viewtopic.php?id=9922&forumid=72

You were there too.

LBD

P.S. Come to think about it... a higher BC is not going to promote stabilization to an unstable model.

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frnkeore posted this 17 September 2013

This is a better program. it accounts for CG (nose shape) and it also shows what twist rate the bullet needs for traveling in the trans sonic range.

http://www.border-barrels.com/barrel_twist.htm>http://www.border-barrels.com/barreltwist.htm

I only use spitzer bullets and because of their CG being farther to the rear, they also need a little less twist.

Frank

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Wayne S posted this 18 September 2013

frnkeore wrote: This is a better program. it accounts for CG (nose shape) and it also shows what twist rate the bullet needs for traveling in the trans sonic range.

http://www.border-barrels.com/barrel_twist.htm>http://www.border-barrels.com/barreltwist.htm

I only use spitzer bullets and because of their CG being farther to the rear, they also need a little less twist.

Frank Frank, never could get that thing to show anything regarding  twists  AND how many SPITZER  cast bullets have you found to shoot good groups ??   LBD, and what velocities did I specify ??

 YOU had a chance to find out for your self about your 1-14 twist when I offered to send you a few samples of the NOE 55 FN and the MX-3-55.   Since barrel makers decided to  skip 1-11 twists and go from 1-10 to 1-12, and as soon as I can lock down and confirm they can and will cut the length of throat I want.  

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pat i. posted this 18 September 2013

I know it's old school and doesn't require a computer program but I always used Greenhill to decide on twist. Greenhill says an 11 1/2 twist will work for a .666 long bullet so you should be safe with 12 in the velocity range you're talking about.

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John Alexander posted this 18 September 2013

Wayne,

Here are my radical thoughts but I don't mean to offend folks with different opinions.

I believe that looking for the “optimum” twist is the wrong approach. The dreaded “overstabilization” is a phantom. My 8 and 9inch twist Tikka and Savages shoot good 35 grain bullets better than most 14 inch twist rifles of the same weight. And the “optimum” twist for those shorties is probably north of the Hornet's 16” twist. Maybe worrying about optimum twist is appropriate for jacketed benchrest shooters where you need under quarter inch groups but us cast bullet shooters have other more important things to worry about. Just get the twist fast enough and quit worrying about it being too fast.

Don't worry about about all the esoteric hocus pocus about twist. The best fancy methods are no doubt better than Greenhill and really needed for some projectiles but Pat is right for cast bullets the Greenhill formula is reliable (and a bit conservative) for both blunt and spitizer cast bullets in the velocity ranges that we usually shoot. At least it is for 22 caliber cast bullets.

I have shot 22 cast bullets in lengths from .43"(Lyman 225107) to .90 (Mos custom 85grain). In rifles with 8, 9, 10, 10.7, 12, 14, and 16 inch twists and have looked at a lot of oblong and worse holes in targets. (And some of the oblong holes made good groups but obviously were on the edge.) I have never found anything that Greenhill didn't predict if the constant was increased from 150 to about 160.

I have a custom NEI mold that drops blunt bullets .654 long (not much shorter than your .666” (isn't that the devil's phone number or something?) My bullet is stabilized in a one in 14 inch twist. I would be very surprised if a 12” twist wouldn't work with your bullet and a 14' might. There are a lot of 14” twist guns around -- try it.

John

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LBD posted this 18 September 2013

Wayne S wrote:YOU had a chance to find out for your self about your 1-14 twist when I offered to send you a few samples of the NOE 55 FN and the MX-3-55. The offer was greatly appreciated but I was only considering the purchase of a 222Mag.  To date I have no .224” center fire.

LBD

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frnkeore posted this 19 September 2013

AND how many SPITZER  cast bullets have you found to shoot good groups ??  Wayne,

Most all the spitzer bullets that I shoot, shoot well. Take a look at my HV PB thread in this section. That was just a test with the 323366 mold. I have many tapered match bullets that do much better.

Spitzer bullets shot from the case are harder to (but not impossible) to get shooting accuractely.

Frank

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John Alexander posted this 19 September 2013

Wayne,

I only shoot spitzers in competition. When shooting a 22 in competition you need all the ballistic coefficient you can muster because you start with a disadvantage in BC compared with 30 caliber shooters shooting a bullet of the same sectional density.

Many competitors shoot bullets that are spitzers or close to it.

I believe the reason there aren't more is that many custom mold makers don't have the skill to make them.

John

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Wayne S posted this 19 September 2013

John,  care to share pictures of 225 SP bullets &  mold maker that makes a SP .225 ?? There has been a “bit” of a discussion on the  Boolits floum reguarding the 311365 And there has to be any posted groups shot at 100 yds that were impressive. I just cast up a bunch of the 311365's I'll heat treat them this weekend and between an M1A, AR-10T, and a “goofy footed"  M-40, they will get a good test  against semi SP bullet {311299}

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frnkeore posted this 20 September 2013

Wayne, Do you have a link to the 311365 discussion?

Frank

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John Alexander posted this 20 September 2013

"John,  care to share pictures of 225 SP bullets &  mold maker that makes a SP .225 ?? There has been a “bit” of a discussion on the  Boolits floum reguarding the 311365 And there has to be any posted groups shot at 100 yds that were impressive.

I just cast up a bunch of the 311365's I'll heat treat them this weekend and between an M1A, AR-10T, and a “goofy footed"  M-40, they will get a good test  against semi SP bullet {311299}"

Wayne S, If you are a CBA member look in your old Fouling Shots. The bullet I am using has been pictured there several times, August and October 3011 to name two. It is not too surprising that 311365 may be difficult to shoot well if it has as much non bore riding nose hanging out in front as it looks to have in the picture. Not all bullet designs are created equal. The 311299 is an excellent design and most bullets will probably come up short in a comparison.

John

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Ken Campbell Iowa posted this 20 September 2013

3011, eh ? john ...geez no wonder the rest of us can't catch up with you.

ken, still in 2013 ( barely ) ..

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Wayne S posted this 21 September 2013

 John, when you say SP I think 311365, if you were to say semi SP then I think 311299.  taking a 311365, marking it's bore length contact in the muzzle I get 64% of it's total length as being in contact with the rifling. The 311299 comes out to be about 73%

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frnkeore posted this 21 September 2013

While the 311365 ogive makes contact with the rifling, it still has to be forced into it with the powder charge. Here you need a freebore (ball seat) of band diameter and length (2 band length would be better)to align it.

The 311299 uses it's bore riding section to align the bullet to the lands, before the powder charge forces the aft section into the lands and grooves.

Frank

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