When loading, what is an acceptable +/- in grains?

[davidjoe]

Over a sample size of one, you may find a negligable velocity difference, but if you take an average over 10 or 20 rounds, you are likely to see the difference, assuming the variance is detectable by the chronograph being used. Even if the chronograph is not capable to detect such differences, that does not indicate the variance does not exist.

Now having said that, powder charge weight is not the only variable, and for that reason small differences may be perceived to get lost in the noise, but the influence is there and apparent if you look closely enough over several rounds.

Right, I agree, my question was meant to be more along the lines of how wide the loading window is, where the powder to velocity ratio holds constant. I’m thinking that down at undercharge levels, we wouldn’t get as much velocity gain per kernel added, and that at max charge and beyond, we’d see pressure quickly rise, but that in continuing to increase kernels, the energy gets expent in deforming brass, rather than accelerating the bullet.

 

[PracticalTactical]

Right, I agree, my question was meant to be more along the lines of how wide the loading window is, where the powder to velocity ratio holds constant. I’m thinking that down at undercharge levels, we wouldn’t get as much velocity gain per kernel added, and that at max charge and beyond, we’d see pressure quickly rise, but that in continuing to increase kernels, the energy gets expent in deforming brass, rather than accelerating the bullet.

I think what I'm trying to say is there is no "window" within which a powder weight change would not result in an average velocity change. All we could debate is the ratio of velocity change on average relative to a given amount of powder.

Certainly it is not a constant, but you can figure it out for yourself using the calculation method in my earlier post but applied to results from your own loading data for the powder range of interest to you.

 

[PracticalTactical]

How do you measure? Are you throwing a charge into a pan that goes on the scale?

Until I got my V4, I was using either a powder measure or a Chargemaster, and putting the charge on a scale (similar to a A&D, but not Mag Force Restoration), and adjusting the charge by hand (usually using a small scientific spatula to add or remove a suitable number of grains.) It worked, but it was God-awful slow and frustrating. But it got me to within about .04 grains of target weight, as far as I could tell. I didn't use a trickler as I kept overshooting and resorting to the spatula method anyway.

One other thing that may come into play is the scale you're using. Most non-scientific (read: consumer) scales are something less than consistent. Drift in zero and drift in calibration will affect what you see as the charge weight. You can see it by throwing a single charge, and reweighing it several times during your loading session.

Agreed. Many hand loaders confuse readability with accuracy. If they see the scale displays in increments of 0.02 grains, they assume it is accurate to 0.02 grains which is absolutely false.

I did quite a bit of testing with my 0.02 grain Sartorius where I cut a length of wire to weigh the same as my target weight and used it to compare back and fourth throughout my loading session. I found disturbing irregularities that eventually sent me off on a mission to resolve the problem once and for all.

I ended up with a Vibra HT220 with internal calibration. This is the latest version. It's incredible.
https://www.scalesgalore.com/produc...nternal-Calibration-220-g-x-01-mg-px49231.cfm

Problem solved.

 

[Beiruty]

What a 1% (30fps) difference would do at LR

225_ELD-M_3000fps_3030fps.xlsx

1drv.ms

 

[Beiruty]

What case capacity difference and +/- 0.1 would do 1K yards

 

[joshb]

Thrown charges of CFE223. Throw ten, check one, throw ten, check one, repeat.

 

[PracticalTactical]

What case capacity difference and +/- 0.1 would do 1K yards
View attachment 1403641

The interesting thing about case capacity is that the case expands to fit the chamber under 50,000 psi, so the external volume is equal to the chamber itself when fired.

At that point, if two cases weigh the same, the only volumetric variance is related to the extractor groove dimensions which don't vary by brand enough to warrant concern.

I like water weight for theoretical pressure calculations, but I never use that for sorting brass.

I only use cases that weigh within 0.1 grains of each other. Just buy enough brass that you can sort into practical lot sizes of equal weight.

 

[JFrank]

What case capacity difference and +/- 0.1 would do 1K yards
View attachment 1403641

Spreadsheets are nice to have but please show me the 1000 yard target that proves the numbers are correct.

 

[Beiruty]

Spreadsheets are nice to have but please show me the 1000 yard target that proves the numbers are correct.

Do your own testing. My rifle is not the same as yours, I do not shoot as good as you.

 

[JFrank]

Do your own testing. My rifle is not the same as yours, I do not shoot as good as you.

No need for negativity , I always appreciate fellas that take their time and resources to test and post results, what would be cool is if you had a target that correlated with these predictions.
Just for the record I’m not a great shooter just a regular guy and limited in the talent department.
Added- and to be honest, case volume is an area of interest to me and a goal this year is to do a better job of sorting and understanding the affect on the target.

 

[PracticalTactical]

No need for negativity , I always appreciate fellas that take their time and resources to test and post results, what would be cool is if you had a target that correlated with these predictions.
Just for the record I’m not a great shooter just a regular guy and limited in the talent department.
Added- and to be honest, case volume is an area of interest to me and a goal this year is to do a better job of sorting and understanding the affect on the target.

We target shooters as a group tend to pick a data point and pick at it in an attempt to improve our end result, but get so focused on that one thing that we dismiss other contributing factors.

Case in point... Lately I have made a connection between how much clearance over the bearing surface diameter is machined into the free bore diameter in my chamber. My conclusion is that the larger the free bore diameter clearance, the larger angular offset is available as the bullet enters the rifling and by extension of that angular variation, we will find a correlating velocity fluctuation and variations in the point of impact.

With this in mind I set off to chambering a new barrel for my 223 to run Hornady 90 grain ATIPs seated out to 2.700 OAL. The idea is to utilize a long free bore to manage high BC alignment along with a minimal diameter clearance of just a few tenths of a thou. This is more difficult than you might assume.

So far it looks like I'm on the right track as my velocity spreads are mostly single digits, but more importantly, a bad 5 round group is around 0.4 inches and good groups are under 0.2 inches at 100 yards.

This is better accuracy than I have found with any of my barrels with throats larger than 0.225" in diameter with the same free bore length.

So, after all that, just saying, it's not all about powder charges and brass sorting. You will only get so far if the chamber is not done to maximize accuracy.

This is the part where some sloppy chamber guy usually says he set some sort of record somewhere, but that aside, I have trouble accepting a sloppy bore provides any sort of advantage especially with long high BC bullets.

 

[Beiruty]

No need for negativity , I always appreciate fellas that take their time and resources to test and post results, what would be cool is if you had a target that correlated with these predictions.
Just for the record I’m not a great shooter just a regular guy and limited in the talent department.
Added- and to be honest, case volume is an area of interest to me and a goal this year is to do a better job of sorting and understanding the affect on the target.

As a system engineer, we do designs by system modeling. I am sorry if it can out in a rude way.
If you do some testing, please share your results.

 

[jelenko]

As others have said, it depends on your accuracy requirements.
In XTC, for our 'short line' [200/300] loads, +/ 0.15 grains in a 223 is just fine. We're shooting at 2 MOA 10 rings with 1 MOA X rings.
In our long line [600 yards] loads, some will keep the powder charge to within a tenth. Some drop their charges from a progressive and do well/very well.

 

[Mr Wick]

Learning a lot by reading all of this.

Thanks.

 

[CharlieNC]

So you shoot a charge weight ladder and observe a region where heavier, faster loads impact lower. And with work hopefully a node with a stable point of impact. A ballistic calculator does not address barrel harmonics, so you must a target to find out.

 

[PracticalTactical]

So you shoot a charge weight ladder and observe a region where heavier, faster loads impact lower. And with work hopefully a node with a stable point of impact. A ballistic calculator does not address barrel harmonics, so you must a target to find out.

I think what you alluding to is called positive compensation.

That's where you seek a node that results in slower rounds launching at a high barrel oscillation point and fast rounds leave the muzzle when at a low oscillation point. That way they even out over distance and hopefully reduces vertical dispersion at the target.

That's a nice idea in theory, but I think the results would be hard to replicate over a wide range of temperatures. If you can get lucky on occasion, the stars will align nicely.

 

[JFrank]

That’s called overlap and it’s part of long range tuning for Benchrest applications.

This is why we judge targets to determine a winner and not spreadsheets.

 

[CharlieNC]

I think what you alluding to is called positive compensation.

That's where you seek a node that results in slower rounds launching at a high barrel oscillation point and fast rounds leave the muzzle when at a low oscillation point. That way they even out over distance and hopefully reduces vertical dispersion at the target.

That's a nice idea in theory, but I think the results would be hard to replicate over a wide range of temperatures. If you can get lucky on occasion, the stars will align nicely.

Always worked for me. When working up a load during cool weather, choose a charge on the low side knowing what to expect when it's hot. Or vice versa. Of course there is no assurance that a wide node will be found. But the fact that PC occurs complicates the direct application of ballistics to assessing small deviations as the OP asked.

 

[JMayo]

One piece of powder Over....

but never one piece under !

That's just the way i play.

 

[Shooter13]

I do measure each charge. But if I'm a grain over or under, it gets to be a pain in the rear to dump it back and recharge when doing 200 loads in a single sitting. I'm also case trimming and case prepping all at the same time.

You keep saying a grain (39.0 - 40.0) or are you talking .02 hundredths of a grain? As you know that is a huge difference to me. EDIT: let me add this, I shoot short range BR, every weekend to me is the Nationals! I want to win, if you think otherwise you are fooling yourself. I may shoot like crap but I came to win, I will also be shooting some mid range, I'll be there to win (and learn 'cause I've never done it), I won't lose sleep if I don't but I never grew up in the participation generation.