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The Shadow (Moderator)
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Discussion Starter · #1 · (Edited)
This will be long-winded, I'm sure. But is meant ONLY to point out some honest realities about what we think we "know", and how much we really don't when it comes to reloading. After a recent miserably failed thread, I think this may be warranted.

What do we know?
Brass alloy? - Not publicly published, as mainstream standards.
Tensile strength? - Not publicly published, that I know of.
Nomimal variance allowed in case production? - Not publicly published.
Brass cases AND primers are a very very poor indicator of ACTUAL pressures. Better than praying over chicken bones, but not much better than that.
Powder nominal variances? - VERY few published.
Lot numbers tested in public data? - NO.
Who makes our powders? - Not unless you read MZ5's post, AND can stay ahead of supplier swaps.
Powders that DO list variances, and EVERY bottle of powder I've ever seen on the shelves in the past several decades have a warning. They tell you that lots CAN vary by 10%.
We also know that powders continually lose moisture content from Sealed containers, changing the burning rates. We know that no one in the industry(on any large scale) loads powder by weight, that's a reloader thing.
Lots of unknowns there...

If some bozo on the interwebs, or in a gun-rag expounds that XX.X grains of this powder will give you
certain results in your 308-super-ninja-2000, and not be over-pressure. Should you REALLY take his advice as gospel? Not if you care about yourself, those around you, or your equipment.

Lets look at some examples from my copies of the following:
Nosler #6 manual(NB), Nosler online(NO), Hornady #9(H), Current Hodgdon online reloading webpage(HO).
308 Winchester, firing 175gr bullets, with IMR-4895. Max's listed.

NB - 43gr @ 2708fps
NO - 41.5gr @ 2559fps
H - 41.1gr @ 2400 fps
HO - 45gr @ 2704fps

Are some "Lawyered"? There is ZERO basis to make that leap of faith. Re-read what we don't know, what isn't listed about what was tested, and you are left with REASONALBY normal variation in coponents tested, for an unlisted date tested.

Ah, but you say there is a difference in the jackets. Some are super-swinging-sexy-awesomeness, and that's the difference! Is it?? Well, here are some test results, in ALL examples the jump to lands is the same distance, the powder charge is the same, the rifle is the same, only the sexyness of the bullets is different. Powder charge in the 175 however is different, to illustrate a point I'll get to in a moment.






Ignore that some of the traces look noisey. The point is the Average Pressures, and the Velocities. All the same velocity AND pressure. The difference in the 175gr obviously charge, BUT it also has a different lot of that powder. Another reason to not just ASSume you can automatically push lighter bullets faster than heavier at the same pressure. It depends on the powder and multitude of variables.

You think your barrel is "Faster" than another?? Great! Show me the pressure tested proof, I would love to see it! Chrono data without Pressure testing is meaningless. Brass and primers DO NOT accurately report pressure, period, end of story.


Some powders when used in the correct application, have a progressive burning curve; meaning they speed-up or slow-down with pressures. Here is a perfect example in the Creedmoor. The ONLY difference is in the charge amount.




Notice the shape is different, almost a plateau on one of them. Due to that more efficient "Push" you significantly drop the operating pressure, but not significantly drop velocity. The chrono alone does not tell you what is actually happening in that firing event.

Another example of why a chrony alone isn't safe:


That is boardering on a blow-up, but the chronograph would say "party-on, Garth!". That load is dead in the middle of a load manual, but the bullet construction was swapped.


So what about primers? They make a difference right? Well, they certainly can. You CAN also have a particular application where they do not, see below.





Can you swap bullets with no change? Sometimes yes, somethimes no. Both example shown above. Can you Swap primers with no change? Sometimes yes, sometimes no.
So the points I hope I made in all this, is that unless you CAN accurately and repeatedly measure these things, then you don't know what is actually going on. If you don't know, then ALWAYS remember the following basic rules of reloading:

Stop whenever you reach either of the following:
Reached published max charge.
OR
Reached published max velocity.

IF you change something, then start your load process over. If the pain of getting off the couch to go ourdoors and shoot is burdensome, or you consider any part of it a "waste"; you need to find a different hobby, this isn't paint by numbers. Enjoying the outdoors, and LEARNING is a large part of this deal. I understand that not everyone can go out their backdoor and shoot. Again, if it is too burdensome to go shooting, then even if you weren't trying to learn reloading, you likely wouldn't shoot enough to learn the marksmanship part well either.
It's not a judgement, just a matter of reality for your particular situation.
 

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Thanks for your time and trouble explaining this. I do try to make safe loads and have experienced the problems of swapping bullets of the same weight but different construction and design by the same manufacture so I never interchange bullets of the same weight no matter who says it can be done.
 

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Even though I possess a limited degree of intellect regarding internal ballistics, I do find this very informative. I often study various pressure curves, I feel they provide me with some perspective regarding bullets and powders, and how they effect load development. I am not the type that relies on chrony results as the final decisive data function, not me. I focus on the whole picture, in that there are various other effects, that even without the trace evidence, which I can't afford on my meager budget, that can still provide at least some useful insight.

But I do truly appreciate the time and effort you've invested to provide us with this material. I will be spending some additional time studying this post, just so much to be taken in during a single read, but it's holds great value within this hobby and at least for me, it's well worth the study time. I may not understand all of it, but I do have a fairly good understanding of applied physics and their effects.

Thank you!

SMOA
 

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Elk Whisperer (Super Moderator)
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Darkker, I've made it a sticky so it won't get lost in the clutter.

Very informative thread and as SMOA stated, it will take more than one reading (for this caveman anyway) to get all the goody out of it.

So, where do I get one of these pressure trace thingies and how much is it so I can tell 't missus.

RJ
 

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The Shadow (Moderator)
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Discussion Starter · #5 · (Edited)
RJ:
https://www.shootingsoftware.com/pressure.htm
Will cost you about the price of an entry level rifle.
But as many who have used them know, can leave you with so many more questions than you thought you had. Truly is for the technically interested. For a standard cartridge with well published(more than one source) date, there is no reason for it.

Jack:
Those graphs are a recording of the actual pressures in the firing event in a Ruger hawkeye with the strain guage sytem attached. Do a quick search for my posts and you'll see the primers in the "run away" graph above. They do not show "signs" of anything remotely out of the ordinary, no funny extraction, report, recoil. No extractor groove stretch. I do also have a post where I did measure the massive expansion on some brass that was running near the 45,000 psi mark. Good ol Federal soft-headed garbage... But the bit about "different signs in different rifles" is exactly my point. "Signs" are at best a very very poor reporter of actual pressures being run. Which is why you should not use them as your yardstick, so to speak.

Cheese:
The system has you attach a different strain guage to each rifle you wish to test. Then you can plug any rifles guage into the computer and test away.
 
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