Confused by powder test results!

[Allen Corneau]

Howdy folks,

I recently did a powder test for a load and I'm having a hard time comprehending the results. I'll try to describe the process as best as I can and I'll leave out unimportant details to keep things short as possible.

I loaded five rounds of each load, 0.2 grains apart, which I will call A, B, C, D, E, and F. At the range I had a target with a common horizontal line and separate vertical hash marks so I could see any vertical shift and I ran my chronograph for the whole test. Wind was sub-5 MPH and I had a wind flag at ~20 yards.

After five sighter/fouler shots, I shot one shot of load A at the first hashmark, then one of B at the second, C, D, E, and F. I let the gun cool about 10-15 minutes, then ran the second shot for each load starting with F, then E, D, C, B, and back to A. Let the gun cool, then shot A-F again, continuing until I had run the full series for five shots for each of the six loads in this zig-zag manner.

When I loaded the chrono data into a spreadsheet, I rearranged the info so I could graph load A shots 1-5, then load B shots 1-5, etc. This is where things get weird...

The first two shots of each load are significantly lower than the next three, like 60 to 75 FPS lower. Across all six loads, all of the first two shots are lower than the velocity jumps for the next three, and with a few exceptions, the velocity continued to rise slightly as the test went on. (The chrono didn't capture the last shot on load F.)



Oddly enough, I shot five rounds of two other loads right after this test and they did not exhibit this increasing-velocity behavior.

No, this is not a new barrel, it has about 1,200 rounds on it. Yes, the barrel was cleaned after the previous range session as usual.

The targets didn't seem to show any obvious correlation between the jump in velocity between series 2 and 3. (Unfortunately, I didn't seem to have a clear winner with the loads, so that's annoying as well.)

Any thoughts on what is going on here?

 

[243winxb]

I let the gun cool about 10-15 minutes,

Barrel heat increased pressure/velocity on shots 3, 4, & 5.

 

[Steve Donlon]

It could have been the air warming up also

 

[Bill Norris]

Barrel heat increased pressure/velocity on shots 3, 4, & 5.

THIS ^^^^^^^

 

[Allen Corneau]

Barrel heat increased pressure/velocity on shots 3, 4, & 5.

But why such a dramatic change between the second and third series?
By the start of series 3 there had already been 17 shots down the barrel with two cooling periods intermixed.

EDIT to add: I think you missed the part explaining how I did the test. Shots 3, 4, and 5 would have been the first shot each at targets C, D, and E, not the third, fourth, and fifth shot of the same load at the same target.

I purposefully did this test in the manner to spread out any chance of barrel warming or fouling affecting any one load.

 

[Longrange57]

Howdy folks,

I recently did a powder test for a load and I'm having a hard time comprehending the results. I'll try to describe the process as best as I can and I'll leave out unimportant details to keep things short as possible.

I loaded five rounds of each load, 0.2 grains apart, which I will call A, B, C, D, E, and F. At the range I had a target with a common horizontal line and separate vertical hash marks so I could see any vertical shift and I ran my chronograph for the whole test. Wind was sub-5 MPH and I had a wind flag at ~20 yards.

After five sighter/fouler shots, I shot one shot of load A at the first hashmark, then one of B at the second, C, D, E, and F. I let the gun cool about 10-15 minutes, then ran the second shot for each load starting with F, then E, D, C, B, and back to A. Let the gun cool, then shot A-F again, continuing until I had run the full series for five shots for each of the six loads in this zig-zag manner.

When I loaded the chrono data into a spreadsheet, I rearranged the info so I could graph load A shots 1-5, then load B shots 1-5, etc. This is where things get weird...

The first two shots of each load are significantly lower than the next three, like 60 to 75 FPS lower. Across all six loads, all of the first two shots are lower than the velocity jumps for the next three, and with a few exceptions, the velocity continued to rise slightly as the test went on. (The chrono didn't capture the last shot on load F.)

View attachment 1673184

Oddly enough, I shot five rounds of two other loads right after this test and they did not exhibit this increasing-velocity behavior.

No, this is not a new barrel, it has about 1,200 rounds on it. Yes, the barrel was cleaned after the previous range session as usual.

The targets didn't seem to show any obvious correlation between the jump in velocity between series 2 and 3. (Unfortunately, I didn't seem to have a clear winner with the loads, so that's annoying as well.)

Any thoughts on what is going on h

Don't think the zig-zag approach will get results you are looking for. You have lots of powder residue built up after that many shots. Clean barrel and shoot same number of foulers before each .2 gr powder increment. This allows for exact same conditions for each loading. I have shot certain powders that are very dirty and seen 75 fps increase across 40 shots with the exact same load. This will give you a better chance of nailing down a consistent load.

 

[Allen Corneau]

Don't think the zig-zag approach will get results you are looking for. You have lots of powder residue built up after that many shots. Clean barrel and shoot same number of foulers before each .2 gr powder increment. This allows for exact same conditions for each loading. I have shot certain powders that are very dirty and seen 75 fps increase across 40 shots with the exact same load. This will give you a better chance of nailing down a consistent load.

In my competitions (HP Silhouette) the gun/ammo has to be able to be good all day without cleaning, so about 100+ shots a day. I can't use a load that only shoots good when the barrel is clean.

 

[Clancy]

I mean this with all due respect, but there’s a lot going on here.

Did you do a seating depth test first?

5 shots is 2 or 3 too many for a powder charge test, especially when you’re looking for common POI. The condition change alone is enough to run it.

Round Robin is the worst way to test loads. Let’s stop that.

I’d imagine your velocity increase was from the air and chamber warming. The poor groups are from the above.

No need for spreadsheets and chrono data until you find something that shoots well and get ready to test it out over several sessions and conditions.

I’d go back with a clean dry barrel…. shoot a depth test then go back again with a clean dry barrel and shoot a charge weight test. All of this with 2-3 shot groups.

If you’ll tell us what it is, I bet we can narrow it down for you and save some components.

Again… I don’t mean to sound rude I was just kinda shocked at how this test was conducted. I’m here to help!

 

[Longrange57]

I mean this with all due respect, but there’s a lot going on here.

Did you do a seating depth test first?

5 shots is 2 or 3 too many for a powder charge test, especially when you’re looking for common POI. The condition change alone is enough to run it.

Round Robin is the worst way to test loads. Let’s stop that.

I’d imagine your velocity increase was from the air and chamber warming. The poor groups are from the above.

No need for spreadsheets and chrono data until you find something that shoots well and get ready to test it out over several sessions and conditions.

I’d go back with a clean dry barrel…. shoot a depth test then go back again with a clean dry barrel and shoot a charge weight test. All of this with 2-3 shot groups.

If you’ll tell us what it is, I bet we can narrow it down for you and save some components.

Again… I don’t mean to sound rude I was just kinda shocked at how this test was conducted. I’m here to help!

This!

 

[SpencerC87]

The first thing I would have to ask is are you 100% sure you shot the correct charges at the correct target and didn't mix the order inadvertently? I've never seen a velocity swing like that without some sort of mix-up. I would recommend doing the same thing over again, or a version of it, and if you see it happen then you have to question the quality of the powder. Having a single charge weight have a velocity increase like that over 30 rounds is just plain unacceptable and barrel heat, fouling, environment don't account for that sort of change. As an F-classer, Having over 100 rounds on a barrel before cleaning is very normal and velocities must and do stay consistent throughout, if not, you must change something.

What cartridge are you shooting?

 

[Allen Corneau]

... Did you do a seating depth test first?

... 5 shots is 2 or 3 too many for a powder charge test, especially when you’re looking for common POI.

... No need for spreadsheets and chrono data until you find something that shoots well and get ready to test it out over several sessions and conditions.

I had already done several other wider powder tests, so these six loads at 0.2 grain spread was dialing in on the best zone.

Yes, seating test had already been done on some previous testing.

Think of the testing methodology as five consecutive one-shot powder ladder tests, they just happen to be done all on the same set of targets. Whether you go low to high or high to low is inconsequential. I just happen to use both.

 

[Allen Corneau]

The first thing I would have to ask is are you 100% sure you shot the correct charges at the correct target and didn't mix the order inadvertently? ...

What cartridge are you shooting?

Yes, I was very careful to make sure each shot went on the proper target. I knew one mistake would mess up the whole 30-shot test.

The cartridge is 6BR.

 

[CharlieNC]

The SD of any given load gives at least as much variability as a 0.2 change in charge weight. Use the average velocity for each charge for characterization. Did you see a charge range where the poi was stable, indicating a node?

 

[Longrange57]

Be nice to know what powder! I've shot thousands of rounds in F-Class and BR with a 6BR. I always used Varget and if and when I shot 100 rounds without cleaning, I normally saw an ES of around 30. I used my chrono at many matches. Even with a full grain spread, I would only see about 60-65 difference.

 

[243winxb]

I think you missed the part explaining how I did the test

Yes i did. Sorry.

 

[Allen Corneau]

... Did you see a charge range where the poi was stable, indicating a node?

Yes, in my previous wider/coarser test this was the range that was the most promising.

 

[Allen Corneau]

Be nice to know what powder!

VV N130 for this load. I also use N135, N140, and N150 for my other loads and have found them to be not-overly-dirty and pretty stable powders. That's why these results are confounding me.

 

[Longrange57]

VV N130 for this load. I also use N135, N140, and N150 for my other loads and have found them to be not-overly-dirty and pretty stable powders. That's why these results are confounding me.

I'm sure you are shooting a bullet in the 95-105 range. If so, 140 would shoot just like Varget and is a very good powder for that weight bullet. The 130 is a little hot for the heavies, and would be more suited for light 64-68 bullets. I shot some 100/200 stuff years ago with the Berger 64 column bullet and used N133 with great results. This could be some of your issue. Try the N140 and take note of Clancy's post! I bet you will see better results.

 

[Allen Corneau]

I'm sure you are shooting a bullet in the 95-105 range. ... The 130 is a little hot for the heavies, and would be more suited for light 64-68 bullets.

I would agree with you there. However, this load is in fact using 70 grain Sierra Match Kings for my Chicken load. The purpose of this load is to have a light-recoil load after the hard-hitting Ram load using Berger 115's and N150.

 

[Steve Donlon]

I don't see how a test like that would really be valid. Human error is going to influence the outcome with a test like that for me. I would have to do multiple test with less variables. I think you might have to much going on. I guess it depends on your accuracy requirements.