Vertical Dispersion - Weighing Primers

[Ledd Slinger]

Many years ago I tested 10 different brands/types of primers. The difference in group size at 100 yards was startling. The primer I was thinking would be the best turned out to be near the worst. CCI's were near the bottom of the results. I would start your testing by comparing different brands/types against each other, and then maybe weigh the best to see if they are consistent.

Yes using different primers can make a huge difference in how a load shoots. But how many different powder/bullet combos did you test with the 10 different primers? How many different rifles did you test the 10 different primers in?

I have done the same thing over many years. Primer changes in load recipes is as big a deal in my book as changing powder type in a load. One rifle with a particular load may shoot a certain Federal primer better than anything else. A different load in that same rifle may produce the best accuracy with a CCI primer. Then you can take a different rifle with the same chambering using the same loads and it may prefer a Remington primer the best.

Point is you need to test every rifle/load with different primers to really know how the accuracy will react.

Cannot come to the conclusion that CCI primers are a poor choice for accuracy because of one test performed years ago while shooting a rifle at 100 yards...I guarantee you that if you would have continued testing loads with primer swaps, you surely would have found a load in a rifle that shoots lights out with CCI and nothing else.

Then to mess your head up a little more, that nice group at 100 yards can easily become the worst group at longer ranges. I've seen it many times. Shot screamer groups at 100 yards with certain powder/primers only to see them open up to barely MOA accuracy 500 and further. So it's best to test at longer ranges.

That all being said...I personally find the best accuracy using Federal match primers. Just my experience.

 

[savageshooter86]

I’ve found huge improvements in my loads on two of my last three barrels by trying different primers. Everything else being the same. It’s worth testing. And I think weighing primers will reduce the number of flyers one may have.

 

[David Christian]

Hey Guys,

I'm not looking to start a debate on the merits of weighing primers, or if it's worth the time investment. I've already decided to give it whirl, and I've weighed out 1,000 of them into groups separated by .02gr mostly (with some extreme outliers culled entirely).

I will say I was pretty surprised by a couple of observations. First, there was way more variation than I was expecting to find. I had a range from 2.28gr all the way up to 2.52gr. Most fell right around 2.40-2.46gr; nice little bell-curve.

It's not my intent to mix any weight groups; just going to load all those that weighed the same together.

That said, I'm not going to get a chance to shoot these until my next match, but as of late I've been struggling a bit with vertical in my load. It'll hold 10-ring vertical consistently at 1,000, but it's not as good as I see from some of the top guys.

I've played around with depth in .002 graduations, but can't seem to tune it any tighter, so here we are. I think my powder node is on point as I'm in the usual velocity range for my barrel length/bullet combo, and generally speaking the gun is shooting quite well.

My question: To those that have weight sorted primers, how much (if any) improvement in vertical did you see?

Bring on the discussion; my body is ready.

Components:
200.20X
N150
Lapua Plama - turned .014"
CCI 400s
.0015 'interference fit'
AMPed every firing

@MikeMcCasland, great set of questions. Primer sorting may be an option. Test sorted versus unsorted and see what happens.

Few other thoughts. Do you use a reliable chrono while testing? I ask as that would be a good way to determine if your ES is not as tight as it could be, which would point towards primer inconsistencies or your powder node being slightly off (for a 20 shot string an ES of 20 or less is ideal).

if your ES is tight, your challenge might be position related while firing, scope magnification/mirage issues, or seating depth issues.

If your ES is not ideal, you could examine your brass prep and/or do a simple test at LR.

Load up 3 rounds per charge weight, in .1 grain increments surrounding your current load. For example, if your current node was 50.3, then load 50.1, 50.2, 50.3, 50.4, 50.5. Shoot them round robin at 1,000 yards to see if any of them sing for you (keep same POA and measure vertical dispersion...don’t worry about horizontal).

From direct experience I can share that @dmoran helped me tremendously in identifying positive compensation at 1,000 yards by tweaking my node up or down by a single .1 grain charge. It works miracles to test this!

Let us know what you find.

 

[KY_Windage]

Then to mess your head up a little more, that nice group at 100 yards can easily become the worst group at longer ranges. I've seen it many times. Shot screamer groups at 100 yards with certain powder/primers only to see them open up to barely MOA accuracy 500 and further. So it's best to test at longer ranges.

I do test at longer ranges, but I find the loads that do the best at 100 yards also do the best at 600, 800, etc.

Whatever the dispersion angle is at 100 yards, it is only going to get worse as you increase the range.

 

[KY_Windage]

That's the first thing I do in any sorting exercise to test for significance.

Yes, please, somebody test!

'Cuz I'm not seeing any reason to pay attention to primer weights. Lots of other things, but not that.

 

[Ledd Slinger]

I do test at longer ranges, but I find the loads that do the best at 100 yards also do the best at 600, 800, etc.

Whatever the dispersion angle is at 100 yards, it is only going to get worse as you increase the range.

Most of the time - yes. But that has not 'always' been my experience. I've had targets at 100 yards lie to me enough times that I no longer even test loads for long range rifles at 100. I now consider it is a waste of my time and money. You'll never get a true depiction of vertical dispersion in a group at 100 yards.
All my initial load testing is now done at 500 yards. Then test farther out with the most promising groups from 500.

 

[KY_Windage]

Well, to be honest, while I see dispersion as I move out, I rarely see vertical dispersion without close to equal horizontal dispersion.

But testing at 500 or even 300 yards introduces too many environmental variables for me to try to make that my primary test range.

 

[Rocketvapor]

You guys don't find that quartering, or head on or tail winds give some vertical at range?

 

[MikeMcCasland]

@MikeMcCasland, great set of questions. Primer sorting may be an option. Test sorted versus unsorted and see what happens.

Few other thoughts. Do you use a reliable chrono while testing? I ask as that would be a good way to determine if your ES is not as tight as it could be, which would point towards primer inconsistencies or your powder node being slightly off (for a 20 shot string an ES of 20 or less is ideal).

if your ES is tight, your challenge might be position related while firing, scope magnification/mirage issues, or seating depth issues.

If your ES is not ideal, you could examine your brass prep and/or do a simple test at LR.

Load up 3 rounds per charge weight, in .1 grain increments surrounding your current load. For example, if your current node was 50.3, then load 50.1, 50.2, 50.3, 50.4, 50.5. Shoot them round robin at 1,000 yards to see if any of them sing for you (keep same POA and measure vertical dispersion...don’t worry about horizontal).

From direct experience I can share that @dmoran helped me tremendously in identifying positive compensation at 1,000 yards by tweaking my node up or down by a single .1 grain charge. It works miracles to test this!

Let us know what you find.

Thanks for the reply!

I'm using a LabRadar for all my non-match shooting, however this gun really liked N150 with everything, and the 200.20X was shooting pretty 'lights out' from the start. I never recorded ES, but my SDs for all test rounds fired at this charge weight (i.e. while I was testing depth, and confirming this was the load) was 6.2. I'm guessing that puts me right at or just under 20 FPS ES. N150 generally seems really good in that regard.

I've read quite a bit about positive compensation, and understood about half of it. My big challenge in testing the theories is the only 1,000 yard range is ~3 hours (one way) from me. Right now I have the ability to test on paper at 300 yards, or on steel out to 600; which means all my testing is done at 300.

I haven't done any load dev on the gun since Oct of 2019, just because I got good testing done in 30-70 degree weather, and figured I'd have the barrel burned out by the time we started getting into the 90s-100s (I will).

 

[dskogman]

It does help, and I just re-read that section so thanks for the cite.

Per my spreadsheet this load is averaging .36 MOA at 300 the 6 times (30 rounds) I've shot it for testing. I'm still inexperienced relative to a lot of guys, but felt like that was good enough to be dangerous in club matches, so just rolled with it.

Your doing well for the short time you've been shooting with us and remember you are shooting against some of the top FTR shooters in the country!

There is lots of good advice here but it's a non-linear progression from 300->600->1000 so for me a .36 MOA @ 300yd gun is not going to compete with the top shooters at 1K. Sorting primers may help but not that much. Remember what Tom said - MOST IMPORTANTLY, does it prefer the seating position and powder charge. If it's as good as it's going to get with N150 you may want to try a different powder/primer/.... If you tried others and it's still no good it could be that its just a decent mid-range barrel. I've got a few in that pile.

Also, measuring vertical at Bayou at 1K with a strong tail wind is a good way to drive yourself crazy. There were full 1-2 MOA vertical shifts out there last Sunday.

 

[davidjoe]

I would think Muzzle Velocity differences are the only logical effect that primer weight variations can make. Any other effect, such a harmonics or wind drift down range would have had to flow from MV differences.

If that hypothesis is true, then even a 50 yard range with D Christian’s chrono recommendation would determine completely, whether weight sorting helps. Plus, if you just go by MV, you take gun handling, bullet variation and the environment out of the equation.

 

[Nightraider]

@Alex Wheeler or @tom do you weigh primers?

 

[Ledd Slinger]

I would think Muzzle Velocity differences are the only logical effect that primer weight variations can make. Any other effect, such a harmonics or wind drift down range would have had to flow from MV differences.

If that hypothesis is true, then even a 50 yard range with D Christian’s chrono recommendation would determine completely, whether weight sorting helps. Plus, if you just go by MV, you take gun handling, bullet variation and the environment out of the equation.

I think ignition rate of the powder via the primer blast would play a part as well. Similar to a combustion engine where the timing of ignition and its consistency is very crucial to proper engine performance.

If there are some weak primers igniting the powder slower than others, although the total end pressures may end up being similar, the pressure curve would be different. Meaning the max charge pressure behind the bullet could be peaking at different points as the bullet travels down the bore.

Just speculation. I have no means of testing pressure curves in a rifle/ammo.

 

[Bc'z]

I've read quite a bit about positive compensation, and understood about half of it. My big challenge in testing the theories is the only 1,000 yard range is ~3 hours (one way) from me. Right now I have the ability to test on paper at 300 yards, or on steel out to 600; which means all my testing is done at 300.

You cant get a 1000 yards on your place for a practice range?

 

[MikeMcCasland]

Your doing well for the short time you've been shooting with us and remember you are shooting against some of the top FTR shooters in the country!

There is lots of good advice here but it's a non-linear progression from 300->600->1000 so for me a .36 MOA @ 300yd gun is not going to compete with the top shooters at 1K. Sorting primers may help but not that much. Remember what Tom said - MOST IMPORTANTLY, does it prefer the seating position and powder charge. If it's as good as it's going to get with N150 you may want to try a different powder/primer/.... If you tried others and it's still no good it could be that its just a decent mid-range barrel. I've got a few in that pile.

Also, measuring vertical at Bayou at 1K with a strong tail wind is a good way to drive yourself crazy. There were full 1-2 MOA vertical shifts out there last Sunday.

To the best of my testing ability (which is limited not so much by the distance as it is the facility itself) I think I'm at optimal depth/powder charge. It's in the same range as what the top guys are doing (200.20x @ 2640 & .012" off).

The facilities I have to test at are pretty lacking, which is why I joined up at Bayou this past week. Currently the best I've got is a 300 yard setup, shot off of wobbly wooden benches (no prone shooting allowed), usually with people shooting close enough to you that you could lean over and look through their scope....i.e. not ideal at all. I'd submit a .36 @ 300 shot on that range is probably tighter than the number would reflect, but I have no way of proving that. Regardless, I've found the vertical lacking as compared to some of the 'higher end' TR shooters.

 

[MikeMcCasland]

You cant get a 1000 yards on your place for a practice range?

I can. Problem is I don't have target frame infrastructure to support the use of an E-Target (or that would stand up to the abuse from cattle/elements), and it's a 1.5hr drive with a 50% chance of cattle being in the pastures that let me stretch to 1k+.

i.e. it's an option, but one that's a risk. I can shoot steel at distance out there pretty easily, but that involves having to shoot over uneven terrain/senderos etc...none of which is ideal for testing vertical at 1k.

 

[dmoran]

@Alex Wheeler or @tom do you weigh primers?

You may want to ask them if they also measure there primers.

In post #16 @tom stated "Being a person who weighs them", and pretty sure, like me, he measures them also.
Not sure what Alex does, but know he's very particular about action pin-fall, which is in the same scheme.

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[rsmithsr50]

you keep thinking that, and we will keep winning.
again,
IT HAS BEEN TESTED AND DOCUMENTED.
IMPROVEMENT IN VERTICAL.
AT 1000 YARDS

Yes, please, somebody test!

'Cuz I'm not seeing any reason to pay attention to primer weights. Lots of other things, but not that.

 

[Rocketvapor]

Test? Why test?
If there is a chance it helps, just do it.
Cull them outliers.

 

[memilanuk]

pretty sure, like me, he measures them also.

I'm probably going to regret this... but besides weight, what other parameter are you finding significant enough to warrant measuring?