Drop at 1,000 yards vs case capacity variance and +-0.1gr of powder

[Beiruty]

A simple illustrative spreadsheet to compute the ballistic drop at 1000 yards versus the case capacity variance of same batch of cases and powder measure drop variance of +- 0.1gr of powder

6_5PRC Hornady Capacity.xlsx

1drv.ms

 

[Rocketvapor]

Interesting.
Case volume range, 0.56 gr (water) gives 2.39" variance in drop (2.39, 2.40, 2.38), and 14fps @ 1000 yds.
Charge from 57.8 gr to 58 gr gives a velocity range of 11 fps.
Combined the velocity range is 24 fps.

Some will claim that shooting in the center of a NODE will eliminate the variance you calculated.

 

[Alex Wheeler]

Ever add powder and see the group print lower at 1k? It happens all the time. Thats why calculating things like this based on velocity and what should happen doesnt work. And why I cringe when people calculate how much vertical a load will have based on its es. It leaves out the most important part of tuning a rifle, barrel harmonics. How the barrel is moving can add or reduce vertical regardless of es and it can make a group print higher or lower regardless of velocity (within reason).

 

[Laurie]

And why I cringe when people calculate how much vertical a load will have based on its es.

Always thought this too. Half the top competitors I know would be shooting from 6 o'clock to 12 o'clock on the black at 1,000 yards instead of their usual well under half-MOA elevations if ES alone had the claimed effects, and that would apply to a good few loads I've happily used over the years. If the claimed effects occurred, 223 Rem would have no utility at all in F-TR for instance at distances over 300 yards given the difficulties in obtaining single-figure ES values over a decent size string. (Despite that, my first L-R 223 F rifle shooting Berger 90s gave me a couple of groups in the fours in a UKBRA 1,000 yard BR comp, despite my being a pretty unaccomplished BR shooter. On the claimed ES / POI linkages, these groups were 'impossible' with ammo that had an ES value in the high teens.)

Yes, it's nice to have the combination giving a 3 fps ES and SD in the ones, but only if the groups are tight too. IME, there seems to be an inverse/perverse relationship in load-testing that sees the strings with the smallest ES values produce the largest groups, and vice versa.

 

[CharlieNC]

Ever add powder and see the group print lower at 1k? It happens all the time. Thats why calculating things like this based on velocity and what should happen doesnt work. And why I cringe when people calculate how much vertical a load will have based on its es. It leaves out the most important part of tuning a rifle, barrel harmonics. How the barrel is moving can add or reduce vertical regardless of es and it can make a group print higher or lower regardless of velocity (within reason).

Exactly. Which is a major aspect ignored by Litz. But the harmonic cycle at play can be determined from the target!

 

[dgeesaman]

Ever add powder and see the group print lower at 1k? It happens all the time. Thats why calculating things like this based on velocity and what should happen doesnt work. And why I cringe when people calculate how much vertical a load will have based on its es. It leaves out the most important part of tuning a rifle, barrel harmonics. How the barrel is moving can add or reduce vertical regardless of es and it can make a group print higher or lower regardless of velocity (within reason).

The new Applied Ballistics book has a nice chapter on the effect of velocity ES and ballistic coefficient variance on vertical. My takeaway is that ballistic coefficient varies from shot to shot and has at least as much effect on final vertical as normal variations muzzle velocity.

So yeah, velocity vs vertical is a nice starting point to calculate but there are a couple of other very significant contributors to vertical in the real world.

 

[6MMsteve]

Ever add powder and see the group print lower at 1k? It happens all the time. Thats why calculating things like this based on velocity and what should happen doesnt work. And why I cringe when people calculate how much vertical a load will have based on its es. It leaves out the most important part of tuning a rifle, barrel harmonics. How the barrel is moving can add or reduce vertical regardless of es and it can make a group print higher or lower regardless of velocity (within reason).

I had the same thing happen at 100yds I added powder and the group shot lower, never could figure it out or never put the harmonics factor into it now I know

 

[JFrank]

A simple illustrative spreadsheet to compute the ballistic drop at 1000 yards versus the case capacity variance of same batch of cases and powder measure drop variance of +- 0.1gr of powder

6_5PRC Hornady Capacity.xlsx

1drv.ms

Have you compared your calculations to your actual target ?

 

[Beiruty]

Have you compared your calculations to your actual target ?

Not at 1000 yards, I do not have access to such paper-target range.

 

[JFrank]

Not at 1000 yards, I do not have access to such paper-target range.

I don’t pretend to know all the answers to this stuff, I’ll leave that to the gurus’s but even at shorter distances I have seen progressive charges not only impact low but sideways variations are quite common as we go in and out of nodes and we know this to be true, that as barrel timing becomes optimized these rounds began to impact a very similar location on the long range target dispite a increase in charge or minor fps. Case capacity /lot numbers seems to play a part I know as per examples I have in a pile that while printing closely in shape or consistency may also print lower in a group, (record brass vs sighter brass would be an example) and while the group looked great it definitely was not where it should have been. Lol it may be interesting to take a reverse approach to Quick load and GRT, start with reality and calculate why it didn’t correlate with the spread sheet.

Probably a dumb idea…
J

 

[RegionRat]

Probably a dumb idea…

Not dumb at all.

Most math models and science start with a careful observation of how mother nature works, and then we go to the board and polish the math till it matches up.

Things like ballistics and aerodynamics have lots of places where there is friction and entropy. Even in the gun tunnels, friction and harmonics have their say in how well we could predict trajectories. It is Mother Nature's way of keeping us humble.

It is a rare day when the theoretical physicists come up with an unobserved behavior prediction from their models/theories and then we corroborate it. Those days are the ones with publications and Nobel Prizes.

 

[Dave M.]

A simple illustrative spreadsheet to compute the ballistic drop at 1000 yards versus the case capacity variance of same batch of cases and powder measure drop variance of +- 0.1gr of powder

6_5PRC Hornady Capacity.xlsx

1drv.ms

Your results on paper are interesting, but honestly they are nothing more than theory. I can almost assure you that you wouldn’t find the real world results correlate. You might find the higher charge prints lower and even that it prints to the right or left of the center line. This is the reality with barrel harmonics.
Dave

 

[Beiruty]

I don’t pretend to know all the answers to this stuff, I’ll leave that to the gurus’s but even at shorter distances I have seen progressive charges not only impact low but sideways variations are quite common as we go in and out of nodes and we know this to be true, that as barrel timing becomes optimized these rounds began to impact a very similar location on the long range target dispite a increase in charge or minor fps. Case capacity /lot numbers seems to play a part I know as per examples I have in a pile that while printing closely in shape or consistency may also print lower in a group, (record brass vs sighter brass would be an example) and while the group looked great it definitely was not where it should have been. Lol it may be interesting to take a reverse approach to Quick load and GRT, start with reality and calculate why it didn’t correlate with the spread sheet.

Probably a dumb idea…
J

This is how I tune GRT Tools. I capture actual MV data and tune the powder/rifle/bullet model to the observed data.

Here is an example. Note: the error between GRT predicted MV and actual MV (by Labradar) is around 0.3%

GRT MV vs MV Greg 3006 180 VLD Elite Hunting.xlsx

1drv.ms

 

[Homerange]

A simple illustrative spreadsheet to compute the ballistic drop at 1000 yards versus the case capacity variance of same batch of cases and powder measure drop variance of +- 0.1gr of powder

A little story about case capacity variance if I may....
A buddy after developing a LR 6mm Rem wanted to push out further to 1000+ and maintain predicable accuracy and continue to group in the 0.3's MOA.
With a new custom platform this time in 7mm Practical (7mm/300 Win Mag) and with load development complete it was time to check/confirm ballistic tables at 1k were precise and apply corrections if required.

So a drive around the farm with rangefinder looking for a safe 1k sight line and spots suitable both ends to shoot and erect a temporary frame.
That done and required elevation adjustments made to the scope a set of 3 were launched and we off after them to see the group.
Much to the horror of the buddy was a quite nice group as tight as expected but 10" high !

The look of bewilderment on this quite experienced handloaders face is something I'll take to my grave as these rounds were from his development notes and loaded just hours before arriving from the same lots of primers, powder and projectiles development was done with.
Mortified and speechless he was as we headed back to where he'd shot from to attempt to deduce how it had gone so horribly wrong.
In his wagon was a good ol' Chrony but no tripod however it was all that was needed for a velocity check of his fresh loads in hope it would reveal the 10" high cause which of course it did....50fps above development, but why ?
You should all know where this is going by now but hang on, all the brass he had was from the same lot....yes and checked for outliers.....yes I did say this chap had some experience but still we all can learn a valuable lesson can't we ?
The 7mm Practical is a blown out necked down 300 Win Mag and with all the fireforming done in a single batch (100 IIRC) some had never had full power loads through them yet so good was the fireforming it was very hard to tell at a glance without a fired case to compare against.

Please mark your case storage containers !

Postscript.
This custom rifle put 3 shots at 1000 yds into a group you can cover with an iPhone 4S !

 

[Ray123]

Nice to know... but I aint gonna worry about any of it. Shot many thousands of rounds at 1000 yds using only thrown charges from a powder measure, and never weighing a Lapua case. Just gonna enjoy shooting, and let the wind blow the bullets on target. Got some pretty decent groups too..sometimes. More importantly learn to put the bullet on target with your mind.

 

[big5ifty]

Calculations are just a guideline for me. I only trust in what I can measure on the target.

 

[Beiruty]

Calculations are just a guideline for me. I only trust in what I can measure on the target.

At least it is a good starting point to know what to expect.

 

[Homerange]

Nice to know... but I aint gonna worry about any of it.

Please think again.
If pushing out to 1k with power to punch through bigger critters and not just paper any competent handloader is going to stoke loads some so with the case capacitance story previous the lesser capacity from a case not fireformed to full pressures results in excessive pressure and certainly enough to loosen primer pockets to effectively trash that brass.
Full power loads into cases that haven't been used with full power loads will result in excessive pressure....so please do worry about simple mistakes that might lead to situations that could danger the shooter or those nearby.

 

[Beiruty]

Interesting.
Case volume range, 0.56 gr (water) gives 2.39" variance in drop (2.39, 2.40, 2.38), and 14fps @ 1000 yds.
Charge from 57.8 gr to 58 gr gives a velocity range of 11 fps.
Combined the velocity range is 24 fps.

Some will claim that shooting in the center of a NODE will eliminate the variance you calculated.

all fps are at the muzzle.

 

[Ray123]

Please think again.
If pushing out to 1k with power to punch through bigger critters and not just paper any competent handloader is going to stoke loads some so with the case capacitance story previous the lesser capacity from a case not fireformed to full pressures results in excessive pressure and certainly enough to loosen primer pockets to effectively trash that brass.
Full power loads into cases that haven't been used with full power loads will result in excessive pressure....so please do worry about simple mistakes that might lead to situations that could danger the shooter or those nearby.

I don't understand your post except being careful which I try to do...but unlike many I don’t sweat the small stuff...in this case the miniscule details, of .1 gr case variation. You can take the same exact case, and shoot it 5 or 10 shot group with it, to eliminate case variations...weigh out to the exact kernel of powder. Mark the case to index it, into the chamber for each shot...done years ago.
You still won't shoot the bullets through the same hole, and you will have velocity variations.
You just can't achieve perfection with all the variables in the components. Powder and primers are made from blended ingredients...no matter how much they try, the kernel of powder or primer mixture is not exactly the same...and the energy output is not the same...especially from lot to lot. Your bullets are not exactly the same, the shot to shot barrel condition is not the same, as more copper and powder fouling is laid down....so I just don't fret the small stuff...like .1 grain difference in case capacity. But for those who like to measure and weigh to the nano level, go ahead it's your time. I'll spend mine shooting and mostly hitting what I aim at...works for me.