Powder Charge to Velocity ratios

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bck1968

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Hi, all. I'm on one of my mathematical mental gymnastics binges again. I shall attempt to be articulate. I swear. And yes, I know I have too much time on my hands and I like Physics far too much. :)

I will say that I know about working-up loads, I have no intention of trying something that "looks good on paper" (or screen, as it were), and so on, and so forth, ad nauseum, ad infinitum.

I've been looking at the ratios of powder charges to velocity, specifically of H4350 for using in a 270 Win. The two bullets I'm comparing are the Partition 150 Grain and the Barnes TTSX 130. References are the specific load data from each bullet manufacturer, and the Hodgdon site itself. Hodgdon lists a Hornady 150 only for that powder. So three different bullets, I would expect different ratios, but at least some consistency within bullet types if not across the board. But that's not what I've found.

Thus far I've found, at least within 4ish grain ranges, the ratios tend to be very linear, though my number-crunching has not been exhaustive. I'm probably the last person here this is news to but it's not what I expected.

Here's what I come up with.

Barnes 130 TTSX:
Hodgdon Ref: 45.78 fps/grain of H4350
Barnes Ref: 49.09 fps/grain (A roughly 7% difference, but so far, so good)

Nosler 150 Partition
Hodgdon Ref: 49.66 fps/grain ("repeating, of course", and for a Hornady bullet, but consistent with previous measurements)
Nosler Ref: 62.50 fps/grain

Wait. What? That's a 26% difference.

Even my Hornady guide, which shows a very linear progression from 2500 fps to 2900 fps works out to 52.63 fps/grain for that powder for their 150 grain 270 win loads.

So, I see there being two possibilities, given that I've rehashed the numbers a few different ways.
1: There's an error in Nosler data (not bloody likely)
2: I'm missing something. (very bloody likely)

So there's my question, Gurus. What the hell am I missing here?

Cheers!
 
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Not missing anything.

Best of luck , you'll never be able extrapolate any data with certainty.

Too many factors outside of that shell casing that effect things when that powder ignites.Your linear burn is especially not going to be the same between two different bullets.

The way one powder may burn with your rifle and shell may not correlate to the characteristics of the next powder with rifle/shell combo.

Remember also that their data is derived with equipment much better than ours and what is published is done so with liabilities and safety at the forefront.

I used to run excel sheets and record all my data , I quit after a while as you cannot keep up and it gets labor-some , now I develop my loads and the only thing that goes on the data sheet is the specific load I choose.
 
I think of pressure vs powder as the front half of a bell curve graph, slow gradual until you get close to max, then steeply climbing until boom.
Now days I have a little black book, in which my favorite loads and work up data for individual rifles goes. Favorite loads in the back of the book.
 
OP, what you're missing is velocity/pressure and powder charges don't work proportionately. Especially when they approach maximum pressures.

Lots of newbies have had some serious kabooms from such assumptions.

This can be found out very quickly with smaller cases/bores where the pressure curve spikes in a hockeystick pattern, from normal to over max with a half grain increase in powder.

Ganderite can likely explain it in very understandable terms.
 
The only thing linear with powder quantity is the amount of gaz produced during the combustion of that powder. Even pressure isn't linear because as the powder burns, the bullet moves through the barrel and the volume containing the gaz expands.

Locally, every function can be approximated by a linear function, so you might see something linear for small variations of powder in a given cartridge with a given bullet, but the math you're trying to do with 2 different bullets over the whole span of the load makes no sense whatsoever.
 
Pierre Van Der Waldt wrote a book - African Dangerous Game Cartridges - identifying this - it is called Velocity to Charge Value (VC). He discusses logging the fps gain per grain as powder charge increase and comparing it to published, pressure tested data. At "max safe pressure" for your case, primer, powder lot, bullet lot, throat, lands, etc., that ratio will change. A way of using pressure tested date from their set-up, in your gear.
 
todbartell said:
published load data is bunk
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Okay, that may or may not be true. Could you elaborate on such a blanket statement or do you prefer to leave it at the ad hominem you just fired at the multiple companies in the industry?

If you have evidence, even anecdotal, to back that up then I would absolutely want to hear it. I'm as much, probably more, interested in the science of shooting as I am making my guns go "bang". It's in my nature to analyze. I need to learn things; I need to know how and why things work. It makes my brain happy.
 
bck1968 said:
Okay, that may or may not be true. Could you elaborate on such a blanket statement or do you prefer to leave it at the ad hominem you just fired at the multiple companies in the industry?

If you have evidence, even anecdotal, to back that up then I would absolutely want to hear it. I'm as much, probably more, interested in the science of shooting as I am making my guns go "bang". It's in my nature to analyze. I need to learn things; I need to know how and why things work. It makes my brain happy.
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I suspect he may be alluding to data for such cases as 6.5x55 and 7x57 to name a few. The load data published for those two particular cartridges is lackluster to say the least. However, most published data is safe for the weakest actions that were chambered in those cartridges, such as early pre 98 model Mausers.

I have rifles chambered for both cartridges in stronger modern commercial actions and they can both safely be loaded much hotter with the latest powders available. I wouldn't dare to use those loads into pre 98 model actions. That being said, I've seen several M38 Swede actions with 308Win, 243Win, 7-08, 30-06, 8x57 and one in 6mmRem. They all seemed to be able to handle factory loads and handloads kept to manual specs very well.
 
bck1968 said:
Okay, that may or may not be true. Could you elaborate on such a blanket statement or do you prefer to leave it at the ad hominem you just fired at the multiple companies in the industry?

If you have evidence, even anecdotal, to back that up then I would absolutely want to hear it. I'm as much, probably more, interested in the science of shooting as I am making my guns go "bang". It's in my nature to analyze. I need to learn things; I need to know how and why things work. It makes my brain happy.
Click to expand...

There is actually quite a lot of data on the internet about the same thing you want to re do.
 
To OP - try to find some of the stuff written by John Barsness on pressure in handholds. He lives near and has access to the Western Powder labs in Miles City, Montana. He has written several pieces on "old wives tales" regarding pressure signs, about coatings and deterrents, about how a home hand loader can and can not reliably use loading data.
By and large, I notice manuals like Nosler, Speer and Hornady specify the brass used (but not the lot), the primers used, the powder loads, often the COAL and barrel length, that they used in their pressure barrels. There is no information given as to "jump", exact chamber dimensions, etc. so it is a bit of a leap of faith to believe that their results are going to be lockstep with the results from your gear. All this confounded by pronouncements about so many grains of powder being "best" or giving X feet per second, with no mention of brass lot, primers used, jump/freebore, and so on.

Much of this stuff has been worked over for years - but often by people without "scientific" apparatus. Another good read is stuff by Phil Sharpe - he actually did have access to and used a ballistic pendulum to "scientifically" evaluate powder and loading performance. Many other writers sold a lot of articles but their "science" is rather thin.

I also notice a tenuous connection being made between what high end bench resters or high power shooters do with their exquisitely built and maintained firearms being applied to off the shelf Remingchester hunting rifles. A decent shooter with a 2 MOA rifle/load with appropriate bullets will take a lot of big game out to 350 yards or so, but won't win many competitions these days... And a 1 or 1/2 MOA rifle/load won't make much difference to that shooter... And now I am spouting off heresy!!
 
The velocity gains arent linear because the topography of powders make a difference in burn rates. They calculate burn rate with loose powder outside a cartridge. When a powder lays in a cartridge, the volume and sq inches of said powder exposed to the spark changes how much and how fast the powder in converted to gas.

And yes most load data in bunk is the sense that it is impossible to account for all factors when companies make up load data and for obvious litigious reasons, round down to be on the safe side.
 
damullet said:
The velocity gains arent linear because the topography of powders make a difference in burn rates. They calculate burn rate with loose powder outside a cartridge. When a powder lays in a cartridge, the volume and sq inches of said powder exposed to the spark changes how much and how fast the powder in converted to gas.

And yes most load data in bunk is the sense that it is impossible to account for all factors when companies make up load data and for obvious litigious reasons, round down to be on the safe side.
Click to expand...

But some load data are just completely boink. If I use titegroup to load a 9mm with a FMJ 124grn, I get similar velocities as published data. If I use H110 to load 300grn FMJ in 50AE for a desert eagle (the same gun that Hornady and Hodgdon's allegedly used to develop their loads), I'm at 15-30% slower and my gun won't even cycle until I'm close to max load. Others get the same result that I get. So in this case, published loads are downloaded enough to be completely useless.

Hornady sells bullets, ammos, and publishes loads. Ironically, if you buy a Hornady bullet, and load an ammo using it's load data, you get something that is not even close to a hornady ammunition. If you use Hornady's max load data for a 325grn bullet, you'll be lucky to get 1250 fps, but their ammo kick like a mule and fly around 1430 fps.
 
You’r e trying to deduce way too much with way too little.

Nosler developes their loads in a Wiseman pressure barrel, minimum spec everything. Not surprisingly if you take your match chambered minimum spec chamber rifle you might even get the same results. Throw it in a remchester or a rugage and you might get anything.

Speer developes their loads in a pressure barrel and then grabs a rifle out of the gun room to report “real world velocities”. Thats fine, but their real world may be different than yours.

Hodgdon aint talking much about details, but much of their pressure data is copper crusher.

Barnes has been all over the place in their data over the years, and its mono bullets. In the real world your final field derived maximum load could be just about anything. They scare me.

Given the hodgepodge of methodology in developing the loads and the wildly differing velocities from barrel to barrel trying to calculate a linear ratio to a couole decimal points is pointless.
 
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