Article: A Unified Theory of Cast Bullets in TFS

45 2.1
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Article: A Unified Theory of Cast Bullets in TFS

Post by 45 2.1 » Mon Mar 11, 2019 8:15 am

Would you post your article here so it can be discussed?

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mtngun
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Re: Article: A Unified Theory of Cast Bullets in TFS

Post by mtngun » Mon Mar 11, 2019 9:14 am

Thank you for being interested in my crazy ramblings. :)

The TFS article was a summary of a thread on this forum, here: A Unified Theory of Cast Bullets

I was reluctant to put forth a "big theory" because it sounds cocky. I'm sure it overlooks some things and can be improved upon. Nonetheless it is a start, and it's based on what actually works as proven by competition results.

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Re: Article: A Unified Theory of Cast Bullets in TFS

Post by 45 2.1 » Mon Mar 11, 2019 9:17 am

It would be difficult to discuss it item to item without the text here as it was presented........................

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Re: Article: A Unified Theory of Cast Bullets in TFS

Post by Joe Ambrose » Mon Mar 11, 2019 11:54 am

Hi Dan you know me by a different name of Starmetal. I too would like to see the article that you wrote in the Fouling Shot so we could discuss it here. I believe it would be beneficial to all of us.

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Re: Article: A Unified Theory of Cast Bullets in TFS

Post by mtngun » Tue Mar 12, 2019 6:21 am

Here is the text. It is merely a condensed version of the forum thread.

A Unified Theory Of Cast Bullets
by Dan Lynch

For as long as people have been shooting cast bullets, we’ve wondered “what makes cast bullets fail? Why can’t cast bullets shoot as fast and as accurately as jacketed bullets?” And if you are a CBA competitor, you probably also wonder “what kind of load is most likely to win in CBA competition?”

Well, I am not (yet) a CBA competitor – that will have to wait for retirement – but nonetheless I follow CBA match results, looking for insight into what works and what doesn’t.

What follows is an attempt to identify the QUANTIFIABLE characteristics of successful cast bullet loads – things that can be measured. This article won’t attempt to cover the QUALITATIVE characteristics of successful loads – things like bullet design, bullet fit, barrel quality, etc.. Certainly some bullet designs shoot better than others, and some barrels shoot better than others, etc., but I don’t know how to quantify those things.

I started with a broad sample of gas check loads (I’ll save plain base for another article as I feel I still have a great deal to learn about plain base bullets) used by CBA competitors that averaged 10-shot one MOA or better at 100 yards. I did NOT attempt to include every single one MOA load shot in CBA history from the beginning of time – that would have required a great deal of effort, and besides my TFS collection is not complete. My sampling process was somewhat random (skimming through old TFS’s), the loads and groups chosen for my table may not have been the best performance ever turned in by that competitor, and many competitors were left out all together. Nonetheless I feel that my collection of winning loads is broad enough to be “representative” of what works in CBA competion.

I used Quickload to estimate the peak pressure and peak acceleration for each load. If the load’s measured velocity was listed in TFS then I used that velocity, otherwise I estimated the velocity with Quickload. (Disclaimer: sometimes Quickload does a great job of predicting pressures and velocities and other times it is not so great.) Quickload works better with some powders than others, and in my experience Quickload does not accurately predict results with N135, which happens to be one of the most popular powders for CBA competition! To calculate the Miller Stability factor, if I was not sure how long the bullet was, I merely made a reasonable guess at its length. Point being, some of the numbers in this table are mere estimates and may not be spot on, however, I believe they are in the ballpark and that should suffice for my purposes here.

<insert ProvenBenchrestLoads.jpg here>

The average peak pressure of winning CBA loads is 35,000 psi. Absolutely no one is winning CBA matches at 60,000 psi. More pressure is likely to cause more deformation or melting of the bullet.

The average RPM of winning CBA loads is 120,000. More RPM = more dispersion due to the inevitable unbalanced bullet. Absolutely no one is winning CBA matches at 200,000 RPM.

The average powder filling ratio is 90%. A powder charge that fills the case generally burns better than a charge that leaves a lot of air space.

The average peak acceleration is 91,000 G. More acceleration = more bullet deformation and tipping.

The average velocity of winning CBA loads is 2100 fps. Higher velocity reduces wind drift, but increases pressure, acceleration, and RPM, all other things being equal. Interestingly, a few winning competitors have successfully dabbled with velocities as high as 2750 fps. One such competitor told me that, yes, sometimes he could win matches at high velocity, but the next day that same load might shoot 3 inch groups. To get consistency, he ended up dropping his velocity down to 2400 fps. There are several things that can cause failure at high velocity, but one thing that catches my eye is that high velocity loads have higher (130,000 – 150,000 G) peak acceleration. There are ways to obtain high velocity without high pressure or high RPM, but there’s no way to obtain high velocity without high acceleration. I suspect that acceleration may be a limiting factor in how fast we can push cast bullets accurately.

Clearly the 30BR is the most winning cartridge for CBA competition. Switching to a bigger case would allow the same 2100 fps velocity at lower pressure and lower acceleration, but then you’d run into either poor powder fill or poor powder burn. No one is winning CBA championships with a 30-06 case stuffed with 4831!

The 6PPC with its typical (for jacketed benchrest) 14 inch twist can be very accurate with cast bullets, but bullet weight is limited to 75 – 80 grains, putting it at a disadvantage for wind drift at 200 yards. On the plus side, 6PPC cast loads run at lower pressures (17,000 – 22,000 psi) than the 30’s (28,000 – 46,000 psi)

Observation on choice of caliber: there seems to be a trade off between wind drift and recoil. The 22’s and 6mm’s can be just as accurate as the 30’s at 100 yards, and are more pleasant to shoot, but the 30’s drift less at 200 yards. A 338 or 375 caliber would drift even less, but recoil becomes a factor. No one is winning CBA championships with a 50 BMG!

The average winning Miller Stability Factor is 1.8. I suspect that is higher than optimal, perhaps due to us growing up with the more conservative Greenhill’s formula. By contrast most jacketed benchrest loads run a Miller Stability Factor of 1.3 – 1.5.. You give up some accuracy when you overstabilize the bullet – not a lot, but benchrest competition is about finding itty bitty improvements. All the big improvements were done a long time ago.

The average winning twist is 12.7 inches. I believe that CBA competitors are correct to have moved away from the traditional 10 inch twist – higher RPM’s increase dispersion, all other things being equal -- but I believe they could go a little slower yet on the twist, perhaps 13 or 14 inches, aiming for a Miller Stability Factor of 1.3 – 1.5 like the jacketed boys.

I didn’t bother listing alloy in my table because nearly all winning loads used linotype. I suspect the choice of linotype is partly due to tradition, because in my own testing I often get slightly better accuracy with a heat treated alloy of 25 – 38 BHN.

While my table does not list it, both nose pour and base pour molds are represented in the winning loads. Likewise, both lathe bored and cherry cut molds are represented. If one type of mold were superior you’d expect it to dominate competition, so it appears that winning bullets can be made with just about any type of quality mold.

While it is not the purpose of this article to single out any particular load, I have to say that Dan Hudson’s 2005 load looks really good on paper, with higher than average velocity, slower than average twist, slower than average RPM, lower than average pressure, lower than average acceleration, and a near ideal (by jacketed benchrest standards) Miller Stability Factor. It shot well, too!

In general, if you want to win CBA matches then you should push a heavy bullet 2100 fps at 35,000 psi, 120,000 RPM, 90,000 G’s, a 1.3 Miller Stability Factor, and 90% powder filling ratio. Any attempt to break out of that range runs into a trade off. For example, I put substantial effort into developing a CBA-worthy load at 2300 fps (the load listed at the top of the table) instead of the usual 2100 fps, but the added velocity increased pressure and acceleration. Switching to slower powders and bigger cases reduced pressure and acceleration but the powder burned less uniformly and generated more carbon fouling. No matter which way you turn, there’s a trade off.

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Re: Article: A Unified Theory of Cast Bullets in TFS

Post by Joe Ambrose » Tue Mar 12, 2019 7:23 am

Dan remember when you had that 200,000 rpm contest on the Castboolit forum? And I almost won it with a SAKO 7mm-08 Carbine Manlicher? Using the crummy LEE 130 gr 7mm bullet? I was shooting 2640 fps with it's 9.5 twist barrel. I was getting .75 groups, but I'd get a pesky flier. That was many years ago. Imagine what I'm doing now. I got a lot of coaching from 45 2.1. The reason those CBA shooters aren't winning with high rpm is because they don't know how to do it. Say you had to drive across the city of New York in a high performance Corvette. Which would be easier, doing it at 25-30 mph or 100 mph? We know the answer to that. It's easier slower. That's why many are stuck in that rut. If you notice today more and more manufacturers have sped up their twist. A couple of manufacturers even stated they wanted to insure the bullet was stabilized out of such calibers as 6.5 and 7mm. Say over 20 years ago how many 22-250's did you ever see with a 9 twist? You see them today. They are leaning the truth. I'm sure you know Bryan Litz. I've spoke with him. He told me that the difference at 1000 yards with a high rpm bullet and a much lower one is a very insignificant amount. He said most wouldn't see unless they had a super accurate rifle and were very very good shooters. I asked him what twist would you have to have to over stabilize bullet to where it would be real inaccurate. He told me he wouldn't tell me because I wouldn't believe him. The fastest twists I've heard of is around 6. So I assume Bryan is talking way lower then that. I know that some of the greats in the pass have fooled with twists starting at 1 turn in 1. One of them was Pope.

Also it's near impossible to strip a cast bullet in a rifle. Ask me how I know. I've shot near pure lead in a fast twist at unbelievable velocity and recovered the bullets along with examining the bore. The bore never showed leading and the grooves on the bullet never showed stripping. I've never seen any rifle cast bullet even show the wider grooves in it at the nose like a revolver bullet when it jumps from the cylinder to the barrel and the rifling is struggling to get a grip on it. Main reason for that is a rifle doesn't have that jump from cylinder to barrel and the bullet is starting as 0 fps being very close the the rifling. Just not going to happen.

I'll let you digest this.

Joe

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Re: Article: A Unified Theory of Cast Bullets in TFS

Post by 45 2.1 » Tue Mar 12, 2019 9:35 am

mtngun wrote:
Tue Mar 12, 2019 6:21 am
In general, if you want to win CBA matches then you should push a heavy bullet 2100 fps at 35,000 psi, 120,000 RPM, 90,000 G’s, a 1.3 Miller Stability Factor, and 90% powder filling ratio. Any attempt to break out of that range runs into a trade off. For example, I put substantial effort into developing a CBA-worthy load at 2300 fps (the load listed at the top of the table) instead of the usual 2100 fps, but the added velocity increased pressure and acceleration. Switching to slower powders and bigger cases reduced pressure and acceleration but the powder burned less uniformly and generated more carbon fouling. No matter which way you turn, there’s a trade off.
Dan, I will have to assume that the last paragraph is your synopsis of "A Unified Theory Of Cast Bullets". I count 34 actual data points.......... that is a very small sample size to base a theory on in using a statistical approach. Other people on the web have done it with less and are still quite unconvincing. Since it was posted in TFS, it will stick as that. There are a whole bunch of people out there that do not belong or adhere to anything the CBA does. They do all these things too with some being a lot more advanced (in terms of groups shot)........ I know several groups doing so besides the ones that have web sites. Why do you think this is a unified theory when you take data from only one group?

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Re: Article: A Unified Theory of Cast Bullets in TFS

Post by mtngun » Wed Mar 13, 2019 4:46 pm

JOE SAID: Dan I have an AR10 with stainless barrel and it's not a match barrel, too boot it has a 7.62 NATO chamber. Using the 30 silhouette bullet that 45 2.1 designed that weighs about 180 grains and cast of 50/50 alloy it will shot consist 1/2 inch groups and sometimes a 3/8 inch group. This is at jacketed velocity of about 2400 fps. On top of that I'm using 867 surplus powder with a 4198 booster. This barrel has a 10 twist. I also have a Browning A Bolt varminter in 308 Win that does 3/8 inch groups with the same load. 45 2.1 has a couple Ruger Scouts in 308 that do about the same.


Joe, the internet is chock full of people claiming amazing groups. According to the internet, people with lever actions are regularly shooting groups that would set new benchrest records. :lol: :lol: :lol: Maybe some of it is true, but most of it is bullshit.

You say you are regularly shooting 3/8 groups -- though as usual in all the time I've been acquainted with you, you do not provide any details or targets. 3 shot? 5 shot? 10 shot? Let's compare your alleged 3/8 inch groups to the CBA national records:
Plain base 5 shot -- 0.190"
gas checked 5 shot -- 0.111"
Plain base 10 shot -- 0.400"
gas checked 10 shot -- 0.300"

Even if your 3/8" claims are true, the CBA boys still leave you in the dust, so why should I give you the time of day?

Here's the deal: the article was about CBA benchrest shooting, published in the CBA magazine, to be read by CBA members, yet you two are telling me that CBA data is no good and I should instead rely on information from random people on the internet? You may be stupid enough to see it that way, but I'm not.

CBA match results are the GOLD STANDARD of cast bullet data. For the article, I used results that had beenPROVEN in competition, in addition to a couple of non-competition loads where the person had posted tons of data and targets. I used only 10 shot groups, not 5 shot or 3 shot. The data points were AGGREGATES -- the average of several groups, not just one group. They were not record groups. As I emphasized in the article, they were not the best groups the person had ever shot, instead I deliberately looked for TYPICAL groups that represent what competitors shoot day after day, year after year, under less than ideal range conditions.

If you want to be taken seriously, enter a CBA match, let your results become part of the official record, and then I'll add your CBA results to my database. If you don't like the CBA, you are allowed to shoot cast in jacketed benchrest competition. If you just want to shoot on your own for fun and brag about your results on the internet, that's fine, but in a world exploding with bullshit claims, no one is going to take you seriously.

45 2.1, if you don't like my data or my article, you are welcome to compile your own data and submit it to the CBA for publication. As I posted previously about my unified theory "I'm sure it overlooks some things and can be improved upon." I hope someone does improve upon it. But you are out of line to come here and demand that I post a reprint of the article because you are too cheap to subscribe to the CBA and too lazy to to read the thread that has been up for two years, and then piss on my article without offering anything constructive besides the same old BS claims you've been making for years. You want me to believe that you are a shooting genius, yet you are not smart enough to do a forum search?

Intelligent discussion is welcome, especially when accompanied by documented results, but trolling is not welcome. You two are known trolls.

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