What causes your same load to not be consistently the same velocity?

[Sokam101]

I finally got some good quality Lapua brass because I was sick of lower quality stuff. I went out and tested my normal load and got 2620 fps SD of 4 with 4 shots and the next weekend I went out and I got 2644 SD of 9 with 8 shots fired. 24 FPS average difference.... Same range. Same temp. The humidity of the 2644 was 90% where it was 50% the week before. I used H4350 powder.

I found out a mistake I was making where I was leaving powder in my chargemaster in between sessions for a few days not long. It's climate-controlled in my reloading room so I don't think that mattered too much but I won't keep making that mistake. But can that cause a 24 fps difference?

Any tips for me? I just want consistency with the same loads. It's going to hurt me at prs matches if I cant get this figured out.

Thank you!

 

[morganlamprecht]

can be lots of things if all the variables arent controlled...

powder/primer/bullet/brass lot to lot variance
bore condition...they will typically gain speed the more and more carbon fouling they get
new barrels will also speed up in the first 0-200 rounds depending on how aggressively it is shot/cleaned/etc
new brass vs fired is usually worth 20-30 fps

yes leaving powder out can affect it 24 fps easily depending on where u are...im on the south tx coast (humid) and even tho my garage is A/C, when i tested it years ago, leaving powder open in the garage for 3 days resulted in avg velocities 35 fps slower than powder fresh from the jug...10 round strings shot same day side by side...being in a dryer climate would have the opposite effect

once barrels get to the fully sped up point, they should maintain that velocity within the error of the chrono/load variance with temperature as long as the bore condition is kept in a similar state....until they start to wear and will begin to go the other way and slow down

chrono matters too...optical chronos can be finicky compared to something like the labR or magneto

bottom line is everything needs to be controlled and tracked if you want it spot on time after time...good news is that 24 fps difference is only worth about .2mil @ 1000 yds and wont even be noticeable inside 600 for anyone but the top 10% of shooters under match conditions

 

[ma smith]

FYI - There's a discussion of this very problem in a recent podcast with Briant Litz from Berger bullets. IIRC he discussed how both humidity and ambient temps are variables that alter charge potentcy.

The Everyday Sniper Podcast: Berger No BS BC Part 7, Reloading for Long Range | The Everyday Sniper

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[Sokam101]

FYI - There's a discussion of this very problem in a recent podcast with Briant Litz from Berger bullets. IIRC he discussed how both humidity and ambient temps are variables that alter charge potentcy.

The Everyday Sniper Podcast: Berger No BS BC Part 7, Reloading for Long Range | The Everyday Sniper

The Everyday Sniper Podcast: Berger No BS BC Part 7, Reloading for Long Range This is Part One of Reloading for Long Range Shooting. This is another masterclass lesson on the Do's and Don't of precision reloading. In Part One we go over: Brass Prep Primers and details around Primer depth...

theeverydaysniper.podbean.com

The Everyday Sniper Podcast: Berger No BS BC Part 8 Reloading | The Everyday Sniper

The Everyday Sniper Podcast: Berger No BS BC Part 8 Reloading Welcome to Part 8 of the Berger No BS BC Series, Reloading for Long Range Shooting Part 2. We continue the conversation with Bryan and Emil in regards to reloading for long range shooting. In this episode we talk: Determining your...

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Ill relisten to them. Thank you

 

[Sokam101]

can be lots of things if all the variables arent controlled...

powder/primer/bullet/brass lot to lot variance
bore condition...they will typically gain speed the more and more carbon fouling they get
new barrels will also speed up in the first 0-200 rounds depending on how aggressively it is shot/cleaned/etc
new brass vs fired is usually worth 20-30 fps

yes leaving powder out can affect it 24 fps easily depending on where u are...im on the south tx coast (humid) and even tho my garage is A/C, when i tested it years ago, leaving powder open in the garage for 3 days resulted in avg velocities 35 fps slower than powder fresh from the jug...10 round strings shot same day side by side...being in a dryer climate would have the opposite effect

once barrels get to the fully sped up point, they should maintain that velocity within the error of the chrono/load variance with temperature as long as the bore condition is kept in a similar state....until they start to wear and will begin to go the other way and slow down

chrono matters too...optical chronos can be finicky compared to something like the labR or magneto

bottom line is everything needs to be controlled and tracked if you want it spot on time after time...good news is that 24 fps difference is only worth about .2mil @ 1000 yds and wont even be noticeable inside 600 for anyone but the top 10% of shooters under match conditions

Perfect! I have a labradar. How do you treat powder from different lots? Right now I have 1lb and a 8lb jug. Should I combine them?

 

[smoothy8500]

SD of 4 with 4 shots and the next weekend I went out and I got 2644 SD of 9 with 8 shots fired

Is this random selection of a few rounds really a large enough sample to get valid numbers?

 

[morganlamprecht]

Perfect! I have a labradar. How do you treat powder from different lots? Right now I have 1lb and a 8lb jug. Should I combine them?

i either a) combine from the beginning...or b) keep them separate the whole time

ive taken 3-4 8lb jugs of h4350 and mixed them all making 1 new "lot", but i wont ever just dump a new lot into a lot im currently using

 

[Sokam101]

Is this random selection of a few rounds really a large enough sample to get valid numbers?

They werent even close. No rounds were in the other days rounds ES at all. Just kinda strange

 

[Dthomas3523]

Is this random selection of a few rounds really a large enough sample to get valid numbers?

If you control your variables properly, and have the correct tools (scales, mandrels, etc), with quality components, then yes it is.

If you weigh to the kernel, seat primers the same depth, use quality brass, quality bullets, and monitor things properly like neck tension and such, you don’t need to run 20, 50, or 100rnds across a chrono to get accurate data.

If you don’t control all that.....then it’s not enough.

 

[Sokam101]

If you control your variables properly, and have the correct tools (scales, mandrels, etc), with quality components, then yes it is.

If you weigh to the kernel, seat primers the same depth, use quality brass, quality bullets, and monitor things properly like neck tension and such, you don’t need to run 20, 50, or 100rnds across a chrono to get accurate data.

If you don’t control all that.....then it’s not enough.

Good point. Im working on it and learning. I know my powder being out was a mistake. Im using quality components now. Was using different lots of hornady brass now im on the same lot of lapua brass.

I just got my scale in my auto trickler and I tested my charge master and it wasn't as off as I thought it would be. Only +-.06 gn. The charge master is rated to +-.1 gn

 

[NiteQwill]

Good point. Im working on it and learning. I know my powder being out was a mistake. Im using quality components now. Was using different lots of hornady brass now im on the same lot of lapua brass.

I just got my scale in my auto trickler and I tested my charge master and it wasn't as off as I thought it would be. Only +-.06 gn. The charge master is rated to +-.1 gn

The difference in the Autotrickler vs CM is the how it measures weight. Consistency is key and the way the Autotrickler measures weight is MORE accurate over time. Since reloading is about doing the same thing over and over very well... good equipment translates into better results downrange.

You already saw what happens with leaving powder out. Next, you can take a look at your reloading technique... and check-off the variables from there. At the end of the day, I personally don't chase numbers. If a load shoots well, produces consistent groups, and gives me the ES/SD I want for a given gun and external variable, I stick with it. I only verify my data if something changes (brass, powder lot, etc.). I rather spend time shooting than reloading.

Good luck!

 

[hlee]

The most simple answer is sample bias. Neither 4 nor 8 shots is a statistically representative sample.

 

[Sokam101]

The most simple answer is sample bias. Neither 4 nor 8 shots is a statistically representative sample.

So I should have loaded 100 up and pissed them away to find out the same thing?

 

[spife7980]

So I should have loaded 100 up and pissed them away to find out the same thing?

If you want to know... yes. This is the string you can pull and unravel the whole sweater if you take it too far though.

Once you have developed a base of knowledge after awhile you can recognize where you deviated with smaller samples and after a few of those you can start to suspect where the changes came in.

Just realize that small samples can lead you astray as youve found, maybe the next 5 shots out of the rifle would have been 24fps faster regardless of what point in time they were shot.
And many times you wont have a real answer as to the why, its just something you need to pay attention to and continually work on. Leaving powder out is only one (and probably the obvious answer but still) but there are 100 different factors that could lead to this. Another easy one is that you didnt have the labradar pointed exactly the same and it was cutting across the beam at a bit different angle and it calculated it as different. Hell, without seeing all of your data it could just be one shot thats throwing it off.

Neck tension is the real bugaboo for me. I bet if you had left those original rounds on the shelf anther week they would have shot the same as those from the second weekend. But possibly not. The only way to find out is to test it.

Other wise just get out and shoot, see if it really makes a difference on steel, I bet if you hadnt put a number on the velocity like that you would have hit the steel just the same.

 

[Dthomas3523]

So I should have loaded 100 up and pissed them away to find out the same thing?

Until your load methods are consistent enough to allow for smaller samples to be more representative of the overall picture, then yes, you would have to.

You either have to do a bunch of stuff up front, or run long strings at the end.

For the rounds being run over the chrono did you:

Check the neck tension on them all?
Check shoulder on them all?
Measure powder to a kernel or so?
Seat with a pressure gauge to assure uniform seating friction?
Use a primer seating tool that is actually repeatable?

Etc etc.

If the answer is no to more than one (and possibly even if answer is no to just one), then the odds of not a large enough sample size increase quite a bit

 

[Sokam101]

Until your load methods are consistent enough to allow for smaller samples to be more representative of the overall picture, then yes, you would have to.

You either have to do a bunch of stuff up front, or run long strings at the end.

For the rounds being run over the chrono did you:

Check the neck tension on them all?
Check shoulder on them all?
Measure powder to a kernel or so?
Seat with a pressure gauge to assure uniform seating friction?
Use a primer seating tool that is actually repeatable?

Etc etc.

If the answer is no to more than one (and possibly even if answer is no to just one), then the odds of not a large enough sample size increase quite a bit

Just dont have the kernel one currently.

How do you guys stop humidity from affecting your loaded rounds? Listening to the NO BS BC they say that rounds don't travel well.

 

[Dthomas3523]

Just dont have the kernel one currently.

How do you guys stop humidity from affecting your loaded rounds? Listening to the NO BS BC they say that rounds don't travel well.

It usually doesn’t change enough to mess you up on steel.