Previous Load charge variables from Bryan Litz

[Retired shooter]

Hello All
Somewhere on this forum , I found a thread discussing the differences of velocity in FPS related to powder charge variables.
Example. 29.5 grains of a powder compared to 29.7 grains or even 29.75 grains of a powder. If my poor memory serves me correctly Bryan Litz had information from previous testing. Does anyone remember such an article,?

Is 5/100ths of a grain of powder noticeable in pressure, and can it actually make a difference in the group sizing.
I have found variance in bullet weight from 109.78 to 110.15 grains. (I know I will be told to test it myself,start lower & work up.)
I am asking for information from the " EXPERTs" here. Trying to shoot 6 MM bullet long range.

I assume ( I know what happens when someone assumes) powder charge variance will have more effect on smaller diameter cases than large cases.

At what point do we draw the line, with what we can control, considering the variables we cannot control.
As an after thought how much difference in load development between 110 grain bullets to 115 grain.?

Thank you.!

 

[RegionRat]

If only internal ballistics could be wrapped up in a few paragraphs.....

You draw your lines where you want to. It takes experience to learn to manage your components and how much of your personal quality control inspections you place on your own workmanship. Math models for internal ballistics are not the same as reality, so they can only be used as a guideline till we get our own experience.

If you allow for oversimplification and all the pitfalls those bring, then I will say you can make a linear assumption for a given cartridge over a very short span. For example, suppose we make up an easy hypothetical cartridge for keeping the math easy here.

If this theoretical cartridge goes 1000 fps with 100 grains, and you get 1100 fps for 101 grains, then we can estimate that the change per grain of powder is 100 fps.

Now, if we know your load, we can take a small part of the ladder test, and estimate how many fps per grain of powder you should expect for your 0.05 grain change. You then take that speed difference per grain of powder and plug the speed changes into a ballistic trajectory calculator and decide for yourself if you can live with that. The reality could be more or less, and that is why you end up testing. This math model estimate is just used as a starting point.

A real world 6 BR or 6 Dasher with a 105gr is roughly 60 fps per grain of powder. So, 0.5 grains would mean 30 fps difference, and 0.05 grains is then 3 fps.

The real world isn't linear, so you have to squint when you do these kinds of discussions. Real world tuning is not linear. Not every change in weight will have a 1 to 1 effect on your groups or point of impact. The space of one thread isn't enough to teach internal ballistics or how to set your component tolerances, but lets go just one step farther for the sake of argument and look at bullet mass.

The mass of the bullet is not exactly the same math, but in general it takes the form of kinetic energy to roughly estimate the change in velocity due to a weight change with all other factors being equal.

KE= (MV^2)/2 so you estimate your kinetic energy for your bullet mass and nominal velocity. You will need to use a factor to convert Imperial units to make the math work. To make it easy we will wrap that "2" and the unit conversion as follows:
V*V*M/450240 = KE
So for example your 105 hybrid goes 2850 fps and gives: 2850x2850x105/450240 = 1894.2 ft*lbs
Now suppose you get an accidental one at 106 grains? We do the algebra and back out the velocity:
(450240*1894.2)/106=V^2 so V= 2836.5 fps
then 2850 - 2836.5 = 13.5 fps difference per grain of bullet weight is a rough estimate of that sensitivity.

So, the reason to control powder weights, versus brass, versus primers, versus bullets, are not all equal. The relationships are not the same so some of these are more sensitive than others. As for advice on what to control versus what to roll with....

The ones you watch as a rookie are rougher than the ones you watch as you approach High Master at Midrange, then again at Long Range. Backing out the powder sensitivity as a beginner is easy math, but on a public forum someone will come along and bark at you for doing math at all. Because I don't really care about having my ankles bitten, I will try and answer questions as asked and don't care if the no-maths take offense. YMMV

 

[Mulligan]

This is perfect^^^^^^^^^

CW

 

[Retired shooter]

If only internal ballistics could be wrapped up in a few paragraphs.....

You draw your lines where you want to. It takes experience to learn to manage your components and how much of your personal quality control inspections you place on your own workmanship. Math models for internal ballistics are not the same as reality, so they can only be used as a guideline till we get our own experience.

If you allow for oversimplification and all the pitfalls those bring, then I will say you can make a linear assumption for a given cartridge over a very short span. For example, suppose we make up an easy hypothetical cartridge for keeping the math easy here.

If this theoretical cartridge goes 1000 fps with 100 grains, and you get 1100 fps for 101 grains, then we can estimate that the change per grain of powder is 100 fps.

Now, if we know your load, we can take a small part of the ladder test, and estimate how many fps per grain of powder you should expect for your 0.05 grain change. You then take that speed difference per grain of powder and plug the speed changes into a ballistic trajectory calculator and decide for yourself if you can live with that. The reality could be more or less, and that is why you end up testing. This math model estimate is just used as a starting point.

A real world 6 BR or 6 Dasher with a 105gr is roughly 60 fps per grain of powder. So, 0.5 grains would mean 30 fps difference, and 0.05 grains is then 3 fps.

The real world isn't linear, so you have to squint when you do these kinds of discussions. Real world tuning is not linear. Not every change in weight will have a 1 to 1 effect on your groups or point of impact. The space of one thread isn't enough to teach internal ballistics or how to set your component tolerances, but lets go just one step farther for the sake of argument and look at bullet mass.

The mass of the bullet is not exactly the same math, but in general it takes the form of kinetic energy to roughly estimate the change in velocity due to a weight change with all other factors being equal.

KE= (MV^2)/2 so you estimate your kinetic energy for your bullet mass and nominal velocity. You will need to use a factor to convert Imperial units to make the math work. To make it easy we will wrap that "2" and the unit conversion as follows:
V*V*M/450240 = KE
So for example your 105 hybrid goes 2850 fps and gives: 2850x2850x105/450240 = 1894.2 ft*lbs
Now suppose you get an accidental one at 106 grains? We do the algebra and back out the velocity:
(450240*1894.2)/106=V^2 so V= 2836.5 fps
then 2850 - 2836.5 = 13.5 fps difference per grain of bullet weight is a rough estimate of that sensitivity.

So, the reason to control powder weights, versus brass, versus primers, versus bullets, are not all equal. The relationships are not the same so some of these are more sensitive than others. As for advice on what to control versus what to roll with....

The ones you watch as a rookie are rougher than the ones you watch as you approach High Master at Midrange, then again at Long Range. Backing out the powder sensitivity as a beginner is easy math, but on a public forum someone will come along and bark at you for doing math at all. Because I don't really care about having my ankles bitten, I will try and answer questions as asked and don't care if the no-maths take offense. YMMV

RR
Thank you for all that information, I am trying to wrap my older mind around it.I never enjoyed math, let alone algebra, I did get really good at shop math for machining and fabrication. You guys are way over my head.

Now if you would. Is there some formula to figure pressures. I understand different powders, eaqul different pressures & burn rates. Shooting gas guns recommended pressures are 52,000. Psi.
Using Q/L tells me a charge of 29.7 grains of a specific powder is not acceptable or safe, however! HORNADY, (OR at least their attorneys) call it a max load.

How do we as reloaders, being obsessed as we are to making a perfect cartridge and perfect load combination know what the tolerance is with powder I am sure some out there are well above what the max printed load data is. How do we know the tolerances. Do we accept their numbers. Plus or minus 0

Thank you to all.

 

[Murray Brook]

How do we as reloaders, being obsessed as we are to making a perfect cartridge and perfect load combination know what the tolerance is with powder I am sure some out there are well above what the max printed load data is. How do we know the tolerances. Do we accept their numbers. Plus or minus 0

I assume you may be inferring lot to lot variation in powders. An accurate chrono would give an indication of lot to lot variation and allow you to correct the BA in Q/L and go from there. Just spit balling here.

 

[Dimner]

I trust the powder mfgs the most followed by the bullet mfg, and QL/GRT the least. Now I'm not calling out QL/GRT, I use those programs so often it's comical. But I will not use it for a cartridge and or powder I have never shot before. I need a real world baseline before I'll use the software for estimating.

With a new cartridge and or powder the very first thing I do is take the powder manufacturer book minimum and add 0.5gr to it. Then I take the max load and subtract 1.0 to 3.0gr depending on how large the case is.

I load up those two powder weights with 5 bullets each. Then I goto the range and fire those two loads and record the velocities.

Only after I have this velocity data will I start using QL/GRT. And adjust the software to my observed velocities and measure/input case volume.

 

[Murray Brook]

Exactly what I do. Case volume and all other specs for the load in my chamber

 

[CharlieNC]

The combination of Quick Load / Gordon Reloader will give you a good estimate of charge vs velocity and a ballistic calculator for drop on the target. But no calculation is available to account for the barrel harmonics. Run a charge ladder on a target to determine the reality with a few shots.

 

[Retired shooter]

I assume you may be inferring lot to lot variation in powders. An accurate chrono would give an indication of lot to lot variation and allow you to correct the BA in Q/L and go from there. Just spit balling here.

I have tested and found the powder that produced the best velocity and the bullets to provide the best grouping for the round I am shooting. When throwing powder I just question the tolerance that is an acceptable amount. I work in the hundreths of a grain, not in tenths. I don't know if my shooting, or the target could show the difference. Maybe the chronograph would tell.

My son tells me I have to much time, that I am overthinking the situation.


Thank you to all.!

 

[RegionRat]

Now if you would. Is there some formula to figure pressures. I understand different powders, eaqul different pressures & burn rates. Shooting gas guns recommended pressures are 52,000. Psi.
Using Q/L tells me a charge of 29.7 grains of a specific powder is not acceptable or safe, however! HORNADY, (OR at least their attorneys) call it a max load.

That is too much oversimplification and gets folks into trouble.

We have all seen the big differences between loading manuals and there are already many threads that dig into the reasons why that happens. Rather than add to that pile, I will try and go another way here for a moment.

I will offer only friendly advice similar to flight school.... try to fly two mistakes high.... it gives you time to react to the first mistake before that first one becomes fatal.... Well, the same is true for lots of things, including guns....

If you continually push pressure, you eventually hit overpressure. Wisdom is knowing when you just need a bigger boat....

I'm from the 30-06 era and not recoil averse. But, I know shooters much better (and bigger) than me who have no problem shooting smaller cartridges in order to avoid fatigue. Being in heavy weapons, I didn't pay attention to smaller arms, but the first time I ran an M-16 compared to 30-06 I got the picture. Guys like Dennis DeMille and David Tubb taught me to appreciate efficient cartridges like the 7-08 and 6XC.

Try to keep an open mind so that you can move down or up in energy as required to get the job done, rather than push the pressure onto a cartridge that really doesn't want it.

You have to use enough gun when it comes to killing, but also have the wisdom to know how to use only enough so that the odds of hitting are good too.

Pushing guns (or yourself) is not smart and you shouldn't let your ego stop you from taking advantage of high efficiency lower recoil cartridges, but then at the same time don't push them into the red zone. When the math and the results tell you it is time, then jump up to the bigger gun and don't overpressure the little ones.

How do we as reloaders, being obsessed as we are to making a perfect cartridge and perfect load combination know what the tolerance is with powder I am sure some out there are well above what the max printed load data is. How do we know the tolerances. Do we accept their numbers. Plus or minus 0

Never mind the folks who go into the red zone all the time. Stay a margin away from the maximum average pressure and learn to be happy there, or see the above.

Setting your tolerances is a long drink of water, but it starts with a study of the published load recipes or the use of the internal ballistics models, then you can estimate the trajectory effects with a ballistic calculator. Then it goes into real world tuning and shooting in real world weather. No civilian calculators predict tune effects due to weather, so you must test in your context.

Name your target, set your goal for vertical error, back into the velocity changes, then estimate the error in powder charge. If possible, stay below it with better tooling. (Spend as much time on learning to shoot and DOPE wind as you do playing with everything else. And, get away from the bench unless that is all you plan to do.)

Pre-loaded ammo is a different world than real time loading like Bench Rest. In BR, folks continually adjust the tune as the morning and day changes. With pre-loaded ammo, you learn how forgiving your tune is by testing on several kinds of days with varied temperatures and winds. That tells us if ammo we loaded in California in 70 F in September, has a chance when it is -20 F in Colorado in November. YMMV

 

[DocBII]

Good day,

VV has said in the past to use +/- 0.1 grain of powder for ever grain of case weight difference. This has worked well for me for rifle cartridges and acceptably for pistol cartridges. Not to exceed 1 grain of powder, especially for pistol cartridges. Works well for hunting loads, competition requires changes for conditions.

HTH,
DocBII

 

[Retired shooter]

Pushing guns (or yourself) is not smart and you shouldn't let your ego stop you from taking advantage of high efficiency lower recoil cartridges, but then at the same time don't push them into the red zone. When the math and the results tell you it is time, then jump up to the bigger gun and don't overpressure the little ones.

Being retired, my cash out flow does not allow for the ego to support the larger firepower. I let my son and his .338 LaPua have that arena. That being said I am using the smaller lower recoil more efficient cartridge (6 ARC) To see what it actually capable of.. its the challenge for me, everyone can go bigger I want to try smaller more efficient. After many years of use, I still have all my fingers and hands in working condition, and would like to keep it that way.

Thank you to all.!

 

[Dimner]

ll offer only friendly advice similar to flight school.... try to fly two mistakes high.... it gives you time to react to the first mistake before that first one becomes fatal.... Well, the same is true for lots of things, including guns....

That is one of the best sayings I have heard. Succinct and descriptive for nearly any situation where one needs to plan for error. I'm gonna use that one myself!