Is there a way to mathematically estimate where accuracy nodes will land?

[BHuij]

Hey everyone--

It seems like if the following variables are known, there should be a way to mathematically estimate at least a ballpark figure for best accuracy of a given projectile:


Alloy/hardness
Boolit weight
Boolit caliber/diameter
Barrel twist


I realize other factors go into this too (boolit profile, length, powder coat vs lube, gas check, specific gun, etc. etc.). But a good example of this is my Mosin Nagant 91/30. I read in multiple places that shooting cast boolits through the Mosin, I would find my best accuracy in the neighborhood of 1800 FPS. My own testing and load workup confirmed this, and my Mosin is now capable of shooting at least 2 MOA when I'm having a good day, using a load that I haven't chronoed, but mathematically comes out to just shy of 1750 FPS.

Right now I'm working up a load for the Lee 105gr .358" SWC boolit in my M&P 9. Is there a formula or calculator I can use to estimate where my accuracy node will be, given that I know the alloy, weight, diameter, and barrel twist?

[Rcmaveric]

Only thing I can think of is min and max pressure of the alloy and start a work up that goes 10% ish under minimum pressure to about 10% over max pressure off the alloy. I used to try and estimate load ranges using that method and then comparing it to OTB. Did it work, a couple of times but it also failed me just as often. Now I just a massive ladder test from published loads and see how fast and slow I can push a pill with a given powder and then write it all down. I can normal find few loads with acceptable accuracy with a given powder and bullet and one will be the most accurate or consistent. The one with best accuracy then gets a small grain ladder test to make sure is its in the middle of an accuracy window or node. Then all the accurate loads get logged and the most accurate one gets put under the favorite load. Most often I find my most accurate loads around the max pressure of the alloy. Owe then I load up 50 rounds of that most accurate load and shoot them all off to see what the group looks like. Gives an accurate representation of the statistical average group size and its fun.

Its waste full and wreck less until you start writing it all down and recording your notes and thoughts. Then it becomes science. All is fair in the name of science and I got lots of trigger time. Now if I can just get the government to fund my research project and an electronic powder dispenser and life will be perfect. I don't mind my beam scale but 100 rounds latter I wish I had a faster means.

[Tom_in_AZ]

I’d guess that you could do it with enough testing. But it would probably be easier to just shoot different loads and go with the best one.


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[dverna]

No...there are way too many variables.

But it is interesting that some loads shoot well in almost any gun. The old 2.7 gr of BE under a 148 gr WC seemed to shoot in all my .38 Spl's and in the guns we tested. Another is the Federal Match load in .308. It may not be the most accurate load for a particular .308 but it will shoot well.

I have never put enough shots through a centerfire rifle, but I suspect that a load that works well for the first 1000 rounds, may not be the best load after 3000 rounds as the barrel and throat wear.

[rsrocket1]

A good read would be for you to take a look at "optimal barrel time calculator (http://www.the-long-family.com/optimal%20barrel%20time.htm)". For these calculations, you need to download his macro enabled spreadsheet (there's also a macro-free version) and use it in conjunction with Quickload. It does not take into account a lot of things I would have thought would be important like barrel thickness, maybe even an acoustic harmonic test, but it does seem to work for me. I've gotten very close with several loads in .223, .308 and 7.62x54R where some were right on and others needed a tweak of a couple tenths of a grain up or down.

The spreadsheet is free, but Quickload costs about $150. If you already have it, then you can do this all for no added cost.

edit: I read the white paper again and it does explain why things like barrel thickness profile and bending is not important, only barrel length is important.

[Artful]

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[country gent]

I heard many old High power rifle shooters make this statement on the imr 4895 41.5 grns federal match primer and 168 grn sierra load, LC 852 match and the federal gold medal 168 grn factory load. If it dosnt perform in your rifle then its time to fix the rifle. The bullseye load of 2.7 grns bullseye and a 148 grn HB WC was also spoken of the same way.

Lee enfields barrels were contoured to provide the optimum harmonics for the military loading of the time in 303. I would also imagine there was testing on the barrel contour of 03s and 06s.

One thing Ive seen on my custom built rifles is normally the difference is a lot smaller between poor good and best loads when new and tuned up. If your having to really hunt for a good load then it may be time to look at the firearm

[barrabruce]

well the stepped military barrel was machined to null out or deaden the harmonics of the barrel
I don't know how much truth is in this but it sounds good to me.
I have never figured out how they come to those particular lengths and dimensions

[Jr.]

I would say that far beyond that there is stock stability (flex in Stock material), chamber dimensions vs brass (the brass dimensions and coal), how true the barrel machining is, the consistency of the boolit as well as coating or lube, and of course the ability of the shooter.

It has been proven by members here (not me) that great accuracy can be achieved with the proper combination but these things take time and tests. As mentioned here keeping a written record of your dimensions, load, lube/coating, and total results is the best way to move in the right direction.

[Rcmaveric]

I will add that, I had a hell of a time loading accurate cast bullets until read "Bullet Powders" by John Goins aka Beagle and "Cast Bullets Bullet Loads for Military Rifles" by C. E. "Ed" Harris. Ever since then I haven't had any problems. Those two articles will give you the tools you need to estimate a load range and work up an accurate load. So if I were to estimate were an accuracy node will land, I will tell my self to stop over thinking and use Beagle or Ed's advices. Then load up some ammo, stop thinking and go enjoy some trigger time.

I am not sure how much I am sold on OTB but it does make a bit of since. I think that is why I get several accurate loads (minute of a deer @ 100yards) and one highly accurate (MOA or better @100 and 200 yards) load when I do my development. The highly accurate load may be when the pressures and barrel times align. However it doesn't always work doing the math to estimate it because theory and actuality doesn't always equal them-self due to unknown influences.

[Rcmaveric]

I would say that far beyond that there is stock stability (flex in Stock material), chamber dimensions vs brass (the brass dimensions and coal), how true the barrel machining is, the consistency of the boolit as well as coating or lube, and of course the ability of the shooter.

It has been proven by members here (not me) that great accuracy can be achieved with the proper combination but these things take time and tests. As mentioned here keeping a written record of your dimensions, load, lube/coating, and total results is the best way to move in the right direction.

Science for the win+1