Savage 10 FCP SR in .222 Remington Benchrest Accuracy

[Wm Cook]

Could anyone advice me on twist rate and barrel length to choose for a Shilen tight necked heavy varmint barrel chambered in .222 Remington for my Savage 10 FCP SR? It'll be shot exclusively from a bench with the only objective being small groups. My self imposed weigh limit for rifle and scope with be 12lbs. And I have a lofty target of breaking .5 MOA.

Bullets will range from the 51.8 grain Lyman 224415 to the ~60 grain NOE 225-60-FN-A2. To be added will be the ~70 grain NOE 225-72-RN-B1 because it looks to have good bearing surface. So the range on cast bullets will be from about 52 to 70 grains. Velocity and BHN will be driven by accuracy. Starting out lubed but may shift to PC'd this year. It'll also shoot its share of 52 grain match grade jacketed bullets.

If anyone could spare a couple of NOE 225-72-RN-B1’s so I could look at olgive to cartridge base I would appreciate it. Just PM me and we’ll work out the $.

Or if you have other suggestions for projectiles, powders, velocities, psychiatrist I would appreciate it. I've been shooting cast .22's for about 25 years and its pretty addicting. Nit picky, persnickety, PITA but addicting.

I should be posting a bunch of data on sub sonic K Hornet in the next couple weeks. Only got the NOE 60 grain to trial. Thanks for helping, Bill.

[sigep1764]

Id prolly stick with 1/9. My 1/7 ARs like heavy boolits almost exclusively. I have an Axis in 223 that is 1/9 and it seems to like 55 grain up to 70 grain. I have not gone heavier or lighter.

[Wm Cook]

Sounds positive!
1) What barrel length on your AR?
2) What velocity are you running?
3) What powders you shooting?
4) how much buildup are you getting on your gas port? I have to start up a Ruger Mini 30 and I’m a bit nervous about contamination.

Thanks. Bill.

[Thumbilly]

Looking forward to seeing the results of the K Hornet project.

Thanks,

Bill

[Texas by God]

1-14" twist is the correct twist for the .222 Remington cartridge. At least that is what it was born with. My 1-14" Tikka 22-250 shot cast bullets quite well last year but I wasn't using Bench rest loading techniques nor did I cast my own boolits. Good luck with your project(s)!

Sent from my SM-A716U using Tapatalk

[Larry Gibson]

It's the length of the bullet, not the weight, of the longest bullet that determines the minimal twist rate needed. I would net get any faster than a12" twist with a 14" twist being my 1st choice.

[sigep1764]

Sounds positive!
1) What barrel length on your AR?
2) What velocity are you running?
3) What powders you shooting?
4) how much buildup are you getting on your gas port? I have to start up a Ruger Mini 30 and I’m a bit nervous about contamination.

Thanks. Bill.

The AR's are all 16 inch with one 7.5 inch barrel thrown in. Its running right around 1800-2000 fps or so with 20 grains of W748. I have one AR that is running a test of not scrubbing the barrel, just running Hoppes soaked patches and cleaning the bolt. 1500 rounds so far and no issue. That particular AR has more than 2000 rounds of lead down the pipe with no issue.

[Mk42gunner]

It's the length of the bullet, not the weight, of the longest bullet that determines the minimal twist rate needed. I would net get any faster than a12" twist with a 14" twist being my 1st choice.

I agree with Larry.

14" should be fine with everything except maybe the 70-72 grain boolits. I'm not sure of the length of them.

Every 14" twist .222 I have shot did better than a comparable 12" twist .223, at least with jacketed bullets, I haven't tried cast in them yet.

Robert

[Wm Cook]

Tradition is 1 in 12 or maybe 14 for a caliber like the 222. But if you're running 52 grain jacketed @ 3,200 fps, or 70 grain cast at 1,700 fps are there pro and cons to a faster twist with either bullet.

Like maybe the fact that casting 22's is a challenge and running a 9 twist will accent the imperfections. Or maybe the increased rotation rate messes with bullet lube leaving the bullet after it leaves the barrel? Does that logic hold up?

Someone check my math on this. A jacketed bullet at 3,200 fps out of a one in 12 twist has a rotation of 192,000 rpm regardless of the weight/length. At 3,200 fps a one in nine has a rotation of 256,000 rpm. I think. A cast bullet at 1,700 fps out of a one in 9 twist has a rotation of 136,000 rpm. Both showing a gain of 33%

Will either the jacketed or cast bullet disappear or turn into a pumpkin with the 33% increased rotation? I'm really struggling to understand the effect of rotation on accuracy on weight/length. To be clear, I am taking the position that 70 grain cast will be helped by the one in nine and that the 52 grain match jacketed will not be hurt by the one in nine.

Throw in variables like a lubed or PC'd, the bearing surface of the bullet etc and I'm think I am way over my head and know not of what I speak.

[wmitty]

Isn’t the slowest twist rate that will stabilize the 72 gr NOE boolit the determining factor here? I’ll be watching this with interest as the heaviest boolits I have tried in my .222 ( M 788 REM) are both 55 grains and the 14” twist rate was fine with them.

[Larry Gibson]

Isn’t the slowest twist rate that will stabilize the 72 gr NOE boolit the determining factor here? I’ll be watching this with interest as the heaviest boolits I have tried in my .222 ( M 788 REM) are both 55 grains and the 14” twist rate was fine with them.

Correct

[Wm Cook]

Larry if you would take a shot at poking holes in the following I would appreciate the feedback.

I think I understand twist rate a little better. At least on the heavy/length end of the spectrum. The feedback I got from barrel and bullet makers was focused on the twist rate with heavy bullets and there is little said about light weight bullets and their optimum twist rate. Shilen said that a one in nine twist is marginally acceptable with a 70 grain bullet. That means that a 72 grain bullet being marginally unstable with a one in 9 twist. NOE confirmed this. They said that a 70 grain should stabilize but that you might have to play with the velocity to get it stabilized.

Berger has a calculator on their web site for their jacketed bullets that lets you to play with twist, weight and velocity and it spits out a “you’re ok”, or “you’re not ok” for stability. It’s called the Stability Factor and carries the acronym SG. Greater than a 1.5 is considered stabilized with the maximum SG achievable being 2.49. Variables such as bullet weight, twist rate and velocity can be played with to see how the stability optimization is effected. It can be found here: https://bergerbullets.com/twist-rate-calculator/

Example: With a one in 9 twist the 73 grain Berger BT @ 3,000fps has a SG of 1.47 and it is considered marginally unacceptable. The same twist, bullet at 3,200 fps has a SG of 1.51 and just barely acceptable for stability. But at 1,700fps with the same bullet and twist the SG tumbles to 1.22 and is unstable in the one in 9 twist (remember this is programmed for jacketed, not cast).

Example: With a one in 7 twist the 73 grain jacketed @ 3200fps has a SG of 2.49 and at 1,700 fps the SG is 2.02 with the faster velocity excellent and the slower velocity pretty good stability.

So stability is tied to both weight/length and velocity. The slower the twist the faster the bullet has to be pushed to stabilize. Within reason (above 1,400fps) the faster the twist the slower the bullet (ie cast bullet) can be shot and still reach stability.

This is somewhat supported by the CBA Benchrest results sheets showing that the very few folks using .223’s were shooting 8 twist and bullet weights of 78 to 84 grain @ 1.600 to 1,900 fps. So I'm comfortable in having the .222 barrel coming in with an 8 twist for 70 grain cast bullets. As a dedicated heavy cast bullet shooter I would go for one in 7. Since I'll be splitting time with 52 grain match jacketed bullets I'm hedging my bet and hoping that the eight twist will work for me.

[Mk42gunner]

I don't think your 52 grain match bullets are going to like being spun that fast. Regardless of how the heavy cast boolits do.

Since the rifle is a Savage, you may need to have two barrels with different twists. Or even two separate rifles.

Robert

[Wm Cook]

You might be right Robert but Sierra believes there's no issue with an 8 twist and their 52 grain Matchking in an 8 twist barrel unless you're running hyper speeds. At 4,000 fps a bullet would be turning 360,000 rpm and my guess is that a light weight varmint bullet would disappear between the bench and the target. So there is a point of no return isn't there.

But for the life of me I can't find anything definitive that says that a 3,200 fps bullet turning at 288,000 would loose stability. And to me stability is defined as .25 MOA with jacketed and my targeted accuracy with cast of .5MOA.

I've always put off reading The Bullets Flight cause I'm so old I'll forget what I learn before I can use it today.

Has anyone ever seen specific references to stabilization and twist rate recommendations for non-heavy weight bullets.

[Larry Gibson]

Larry if you would take a shot at poking holes in the following I would appreciate the feedback.

I think I understand twist rate a little better. At least on the heavy/length end of the spectrum. The feedback I got from barrel and bullet makers was focused on the twist rate with heavy bullets and there is little said about light weight bullets and their optimum twist rate. Shilen said that a one in nine twist is marginally acceptable with a 70 grain bullet. That means that a 72 grain bullet being marginally unstable with a one in 9 twist. NOE confirmed this. They said that a 70 grain should stabilize but that you might have to play with the velocity to get it stabilized.

Berger has a calculator on their web site for their jacketed bullets that lets you to play with twist, weight and velocity and it spits out a “you’re ok”, or “you’re not ok” for stability. It’s called the Stability Factor and carries the acronym SG. Greater than a 1.5 is considered stabilized with the maximum SG achievable being 2.49. Variables such as bullet weight, twist rate and velocity can be played with to see how the stability optimization is effected. It can be found here: https://bergerbullets.com/twist-rate-calculator/

Example: With a one in 9 twist the 73 grain Berger BT @ 3,000fps has a SG of 1.47 and it is considered marginally unacceptable. The same twist, bullet at 3,200 fps has a SG of 1.51 and just barely acceptable for stability. But at 1,700fps with the same bullet and twist the SG tumbles to 1.22 and is unstable in the one in 9 twist (remember this is programmed for jacketed, not cast).

Example: With a one in 7 twist the 73 grain jacketed @ 3200fps has a SG of 2.49 and at 1,700 fps the SG is 2.02 with the faster velocity excellent and the slower velocity pretty good stability.

So stability is tied to both weight/length and velocity. The slower the twist the faster the bullet has to be pushed to stabilize. Within reason (above 1,400fps) the faster the twist the slower the bullet (ie cast bullet) can be shot and still reach stability.

This is somewhat supported by the CBA Benchrest results sheets showing that the very few folks using .223’s were shooting 8 twist and bullet weights of 78 to 84 grain @ 1.600 to 1,900 fps. So I'm comfortable in having the .222 barrel coming in with an 8 twist for 70 grain cast bullets. As a dedicated heavy cast bullet shooter I would go for one in 7. Since I'll be splitting time with 52 grain match jacketed bullets I'm hedging my bet and hoping that the eight twist will work for me.

First of all it is, for a given caliber, bullet length that determines minimal twist for stability at a given velocity. It is not bullet weight.

Second, Sierra deals with jacketed bullets so their advice applies to those at the velocity level they are talking. You are talking cast bullets. It is the length of the bullet not the weight.

Couple examples where the Sierra advice is incorrect.; in a 30-06 with a 10" twist the Sierra 220 RN will stabilize at 2400 fps. The Sierra 220 gr MK is a much longer bullet and needs an 8" twist to stabilize. In the 222 Rem with a 14" twist the 55 gr Sierra SP will be stable giving excellent accuracy at 3000 fps. Same load with the longer 55 gr Blitz King will not stabilize. It is the length of the bullet not the weight.

Third, the Sg for full stability comes in at 1.4. Suggest you Google Miller Formula and use it to compute the Sg. Use a velocity of 1800 fps and the length of the bullet and vary the twist rate until you have an Sg of 1.4. Or set the velocity at 1800, the twist at 8, 9, 12, or 14 and vary the length of the bullet until an Sg of 1.4 is found. That will give you the max length of the bullet for that twist.

Yes the weight of the bullet will also be entered because the formula also computes the energy.

Additionally, for the accuracy level you are contemplating with cat bullets, the velocity will be around 1800 fps +/-. Thus you want the cast bullet to be stable at that velocity +/- based on the length of the cast bullet not the weight.

[charlie b]

The simplified stability calculators (like the Miller one) have a couple of constants that you need to know about before using them. They are set for around 2700fps and they assume a 'football' shape bullet, yes, tapered fore and aft. That makes it pretty close for most rifle bullets. Some also ignore things like air temp, humidity and altitude which are very important for the calculation of air density in the equation. FWIW, the weight of the bullet is used in the stability calculation to determine rotational moments, ie, a lower weight bullet of same size will have less rotational mass.

I've had experience both ways with the simplified equations. I've had some where the calculation said they would be unstable and they shot well. And some the opposite. Usually happens when the bullet shape is far off of a football shape, like a 1R nose and flat base, or, one of the low drag designs.

Basically they are a place to start, but, not to be taken as gospel.

[charlie b]

The simplified stability calculators (like the Miller one) have a couple of constants that you need to know about before using them. They are set for around 2700fps (this is for fully developed supersonic flow calculations) and they assume a 'football' shape bullet, yes, tapered fore and aft. That makes it pretty close for most rifle bullets. Some also ignore things like air temp, humidity and altitude which are very important for the calculation of air density in the equation. FWIW, the weight of the bullet is used in the stability calculation to determine rotational moments, ie, a lower weight bullet of same size will have less rotational mass.

I've had experience both ways with the simplified equations. I've had some where the calculation said they would be unstable and they shot well. And some the opposite. Usually happens when the bullet shape is far off of a football shape, like a 1R nose and flat base, or, one of the low drag designs.

Basically they are a place to start, but, not to be taken as gospel.

[Larry Gibson]

FWIW

I've used the Miller Formula , with all the data mentioned entered, for some years now to calculate numerous
bullet stability in 10, 12, 13, 14, 16 and 18" twist 30 calculate and 7,8, 9, 10, 12 14 and 16" twist 224 calculate. Also numerous other calibers. It has always,so far, given spot on answer's. Well cast bullets with Sg's of 1.4 or higher demonstrated excellent stability. Those with Sg"s less than 1.4 demonstrated a lack of stability.

[Wm Cook]

Larry, thanks for the direction on this. Numbers are coming together and evaluations are in process. The day you don’t learn something is the day after you die. I appreciated the help you gave me. Bill.

[charlie b]

I found it to not be as accurate with my .45 cal bullets. The .30 and .22 have closer shapes to the Miller 'bullet'.