Speed

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Last Post 17 June 2021

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makpeter posted this 24 May 2021

Hello everyone

I recently received a new mold MP 227 -75 GC

The first casting was not such a great success

Too eager to see what bullet I'll get

But the next time I follow the rules and is a big success

After casting I have a weight between 66.5 and 67 grain

I once read somewhere that lead cast bullets should not exceed 1900 f / sec

But if the Brinell hardness is above 15 and with powder coating and gas check, you can go up to 3000 f / sec

I have a Brineel hardness of 20 with gas check and powder coating resized to 225

Load Vithavuori N135 - 22.3grains with an average speed of 2700 f/sec

Some fly dead center and others with a spread of nearly 7 inches

At first I thought I had a very bad day, but then no problem with bought bullets

I don't know what i am doing wrong

Greetings

Peter

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delmarskid posted this 24 May 2021

In my experience the results you are getting may be from your bullets being driven too fast. I don't use powder coating but with the BHN you use I get good consistent groups up to 2300 fps. Just guessing here but I think 2500 fps with your bullets is a better fit.

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kootne posted this 24 May 2021

Is your bullet base seated below the neck? That could be an issue. It is hard to tell from your photo but looks like that is happening.

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Spindrift posted this 24 May 2021

I would simply try to reduce the load, first. I think it is generally a good idea to get a grasp on the bullets accuracy potential in the particular rifle, before moving into warp speed. And this is easier at more relaxed velocities.

My observation is, the base-below-the-neck does not affect accuracy much, with coated bullets (but I have not tried this at jacketed load levels).

I coat my bullets after seating the gas check, i «feel» this helps glue the check to the bullet shank.

Would you happen to know the twist rate of your barrel, by the way?

Here are a few european powders I use in the .223

Vihtavuori N110 11-12 grs

Vihtavuori N120 14-15grs

Norma 200 14-15 grs

Vectan Ba9 around 7grs

Vectan A0 7-7,5grs

Vectan tubal-3000 15-17 grs

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makpeter posted this 24 May 2021

Hey

I shoot a HOWA 1500 varmint with MDT chassis and twist 1/10

Seating first the gas checks on and then powder coating was my next tought

I am really fond of it because with sierra TMK 69 grain it shoots beatifull on a good day 100 yards around 0.80" all indoors so no bother of the wind

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makpeter posted this 24 May 2021

Hey

I also make the bullets for me and my son-in-law, I have also already shot with vithavuori N320

For me in the Howa it is not a problem but for my son-in-law who has an AR-15 and then the pressure is too low to eject them

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Shopdog posted this 24 May 2021

Almost don't want to respond because it can lead to "more" questions than answers....oh well.

It's not "speed" that's at issue,it's imperfect bullets. The speed exponentially increases the problems. I shoot a metric tonne of cast 22's in mostly 22-250 but do have quite a few 223's. The latter get a steady diet of one of the 4198 powders. The 22-250's are happy with IMR4831.

Generally,a mould is going to need several casting sessions to get into their sweet spot,not always...

I strive for casting so that weighing becomes a waste of time. Yes,a new batch will hit a scale but along with checking "slump" of finished bullets,this is done to certify alloys moreso than consistency. If a seasoned caster is on his game,you can get the weight consistent to within .1 grain on a 50-70g 22 bullet. When you see .5 showing up,well... there's a hurdle.

Next is,conventional push through sizing is not doing you any favors. Oh,it'll make the bullet round,but it doesn't change the balance one iota. So either go unsized or roll size it(look up roll sizing cases). You can install GC's without sizing the whole bullet. Just like the weight,if your unsized bullets aren't round,before sizing.... well,sizing isn't going to help from a balance standpoint.

The window for accuracy is shrinking as velocity and pressure is raised. To many folks just want answers,and I get that. But it's a series of hurdles,each interacting within nanometers of each other. Take "slump" for example. I use a torque wrench as a handle on a lube sizer. Same alloy,same day,two different bullet moulds will have different slump(technically this is yield) numbers. Same with caliber of bullet.

I don't powder coat,so no comment there. But regularly shoot the 22's at starting JB velocity and pressure with the TINIEST amount of some pretty basic lube. Just the tiny spot above GC. Not saying lube isn't important but,compared to fit,roundness,and uber consistent weight.... it isn't. It causes more problems than it fixes. Not trying to dissuade your PC'ing effort but suggest it's adding another hurdle.... if you're trying to get JB velocity.

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pat i posted this 24 May 2021

I dont see the draw to pushing cast bullets to jacketed velocity speeds anymore. I did it years ago and never gained a thing. An accurate 1800 fps load will be a lot more fun than a scatter gun 2800 fps load anyday. Not to mention cheaper and more enjoyable.

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GP Idaho posted this 24 May 2021

I rarely push cast bullets to jacketed velocities. The hardest pushed powder coated 22's are for my AR and with 55gr bullets the sweet spot for functional reliability and accuracy in my rifle, it's 20gr of 4895. Gp

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Larry Gibson posted this 24 May 2021

"makpeter posted this 2 hours ago

Hey

I shoot a HOWA 1500 varmint with MDT chassis and twist 1/10"

Shopdog's post gives you a good idea of the problem. You have run into the RPM Threshold and are exceeding it. with "normal lubed cast bullets the RPM Threshold is usually between 120 - 140,000 RPM. With your 2700 fps in your 10" twist barrel you are well above that. 140,000 RPM in your 10" twist barrel is right at 1942 fps. You can push the velocity up some with the harder bullets, PC (maybe) and a slow burning powder. However, as Shopdog indicates no matter how perfect we can cast bullets thay will still not be as well balanced as we can make jacketed bullets.

You can shoot 1 - 2 moa with cast bullets at 2700 fps but, truthfully, you won't do it out of a 10" twist barrel/

LMG

Concealment is not cover.........

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Shopdog posted this 24 May 2021

The reason I push them is varmint hunting. Range estimation is critical for making center hits. The flatter the trajectory the better. Next is terminal,the harder the cast bullet,the more frangible.

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Larry Gibson posted this 24 May 2021

Many times what we want to do just isn't going to happen. The limiting factor in your quest is the 10" twist barrel and the bullet design. As I said, you can push the RPM threshold up a bit but not to 2700 fps. The bullets being 7" out (assuming at 100 yards/meters) then the moa probability is close to 14 which is atypical of that velocity with that design of cast bullet at 2700 fps in a 10" twist.

Additionally, I have shot a lot of varmints from small ground squirrels to coyote in size with cast bullet of linotype with 14" and 16" twist 22 Hornet, 222 Rem and 223 Rems at 2400 - 2700+ fps and have found the idea of the bullets being "frangible" enough to shatter (be explosive) to be more of a mythical concept than reality unless a solid bone is hit. Most varmints lack such.

Also a couple years ago I used my 30x60 XCB rifle on PDs. I shot them from 300 to 500 yards. The #2 alloy WQ'd 30 XCN bullet ran 2900+ fps out of the 31" barrel with a 16" twist. It was capable of moa accuracy to 600 yards. Out to the 500 yard up slope I was shooting the PDs on it certainly killed them but there was a severe ricochet problem as the cast bullets were not "frangible" and breaking up even when hitting the harder ground. I have also shot those bullets into wet pack at 300 yards to recover bullets and found no evidence of the bullets shattering or breaking up.

The experience on this forum and others will tell you to get a different mould that has a meplat on the bullet and perhaps a hollow point. Also to drop the velocity down to where accuracy is acceptable. All the velocity in the world won't be of help if the bullet misses.

LMG

Concealment is not cover.........

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M3 Mitch posted this 26 May 2021

Does anybody have an idea of why the 140K RPM limit exists? I have read about it on here and have seen it in real life, but don't have any understanding as to what is actually going on to make the bullets shoot wild above this limit.

Thanks in advance for any enlightenment

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pat i posted this 26 May 2021

I dont think 140k is a limit across the board. In my experience the smaller than 30 caliber the faster you can spin them and the larger brings it down. Only thing I can come up with for that is the smaller the caliber the closer the defects are to the centerline of the bullet. I also dont think 140 or 120k is set in stone for 30 caliber bullets but it does kinda look that way. A quick calculation of the better match shooters twist rate and velocity seems to bear that out. In my opinion if you're wanting to shoot fast to beat the wind going with the longest heaviest bullet your twist will tolerate, I always used Greenhill to decide that, will get you there a lot easier. If you just want to shoot fast for the sake of shooting fast go with a slower twist. Tom Gray talked about bullets being twist limited years ago and I havent seen much to prove him wrong in real life. Of course you read all kinds of stuff on the internet saying otherwise but I havent seen it.

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Larry Gibson posted this 27 May 2021

"Does anybody have an idea of why the 140K RPM limit exists?

A 140K limit does not exist. I never, ever said it was a "limit".

What does exist is an RPM Threshold. That threshold generally[ for ternary lubed cast bullets] generally will fall between 120k and 140k RPM. Exactly where between those numbers depends on numerous factor that pertain to the design of the cast bullet, the alloy, the care in casting, sizing lubing, loading etc. It is called a threshold because if crossed accuracy goes south with non linear group expansion as the range increases. That threshold can be pushed up some.

Also, what causes the inaccuracy when the RPM threshold is crossed has nothing to do with bullet stability. pat I is correct; "If you just want to shoot fast ....... go with a slower twist."

LMG

Concealment is not cover.........

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Larry Gibson posted this 27 May 2021

To answer M3 Mitch's question as to "why" the RPM Threshold exists;

The RPM threshold is that point where accuracy begins to deteriorate when the RPM is sufficient to act on imbalances in the bullet in flight to the extent the bullet begins a helical arc in flight or it’s flight path goes off on a tangent. It is best noted when working up a load as velocity increases flyers begin to happen. Then as velocity is further increased the total group size increases sometimes to the point some bullets fly so far off they miss the target. A further indication the cast bullets at or over the RPM threshold is (or some of them in a load that is on the edge of the RPM threshold) the non linear dispersion of the group size as range increases.

Let us keep in mind the RPM threshold most often falls in the 120,000 to 140,000 RPM range with regular lube groove cast bullets. Exactly where the RPM threshold will be in fps depends on numerous factors; alloy, bullet design, fit, sizing, lube, GC’d and seated square, powder burning rate and the length of the barrel, etc. The RPM threshold may be lower than 120,000 RPM by careless casting and loading techniques or when using very soft alloys with very fast burning powders. Conversely, the RPM threshold can be above 140,000 by careful casting and bullet selection and preparation along with careful accuracy enhancing loading techniques, especially those for cast bullets at high velocity such as using slow burning powders that ignite easily and burn efficiently at lower pressures. The trick is to get the cast bullet to exit the muzzle as balanced as possible with as little deformation to it during accelleration. The more balanced the bullet is and the closer the axis of rotation coincides with the center of mass on exit from the muzzle and during flight the more accurate the bullet will be and thus, the higher the RPM threshold will be.

The RPM threshold is not a set “limit” of RPM or velocity. Best accuracy will be just under the RPM threshold or lower. Useable accuracy can be had above the RPM threshold if the ranges are not long and the accuracy requirement is not small. Keeping .223 cast bullets on a silhouette target out to 200 yards for example or keeping hunting cast bullet accuracy at say 4 moa if the max range to be used is 50 – 100 yards.
Again; the RPM threshold will generally be found between 120,000 to 140,000 RPM with regular commercial cast bullet designs and loading techniques most cast bullet shooters use.

In the chart below I’ve computed the fps for various common barrel twists for 120,000 and 140,000 RPM. For other twists in between anyone shouldn’t find it too difficult to interpolate. These fps figures should give you an idea in what fps range your loads, as you work them up, will probably bump into the RPM threshold and when accuracy will probably begin to deteriorate. Some pundates will crticise this chart saying they, or someone else, gets accuracy above the figures in the chart. For those who understand how to push the RPM threshold up with higher velocity cast bullet loads that can indeed be the case. However, as mentioned, the chart is for the majority of cast bullet shooters who do not care to push the RPM threshold up but simply want to understand where and why accuracy will probably deteriorate with their regular cast bullet loads. This chart was done for them.

RPM……….120,000……….140,000

Twist……….FPS…………..FPS

7”…………1166…………..1361

8”………….1333…………..1555

9”………….1500…………..1750

10”………...1666…………..1944

11”………...1833…………..2139

12”…………2000………….2333

14”…………2333………….2722

16”…………2666………….3111

18”………….3000…………3500

LMG

Concealment is not cover.........

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Wm Cook posted this 17 June 2021

Thanks Larry. The direction you pointed me in several weeks ago gave me a firm push towards understanding ballistics. Now with what you just explained helped me close the loop on understanding even more so about stability with variables such as twist rate/bullet length and cast bullet RPM thresholds.

As far as talking about “fliers”, any one who has “been there, done that, bought the T shirt” could give a lengthy dissertation, with examples and flip charts, about the pitfalls that can cause them.

Sometimes it’s so subtle you have to be wired very very tight to sort it out.

Sometimes it’s a little easier to figure out like simply too much velocity.

Stick with it Macpeter. You’ll get it figured out. BC

I do love chasing accuracy.

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OU812 posted this 17 June 2021

Fit is the most important. I bump my bullets to get them more round and to slip fit into rifling without being pushed back into case when chambered. Use a quicker powder like rel 7 or or 4198 and keep velocity under 2000fps.

Softer alloy (10-12 bhn) and velocity lower than 1700 works great with quicker powders such as titegroup. Fit is very important and has been repeated thousands of times here.