FPS Variance In Groups

[HuntBG84]

I am relatively new to reloading. Recently I was shooting my 300 WSM and 6.5 creedmoor through a chronograph. I was shooting my hand loads in both. The FPS was varying up to about 50 FPS. Is this acceptable? If not, what is an acceptable variance in FPS? I was shooting 5 shot groups.


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[bsnedeker]

From what I've read it seems most guys are trying to get their variance into the single digits. Is 50 FPS variance acceptable? I think it depends on what kind of shooting your are doing. If you are shooting long-range matches it's probably not acceptable. If you are in most realistic hunting situations, yeah, it's probably fine. With a load that is properly tuned for your rifle harmonics a 50 FPS variance shouldn't have much of a POI shift out to 3-400 yards from what I've seen.

That said, I'm no expert in this stuff and I'm sure some of the other more experienced guys will chime in.

 

[mvrk28]

There are two numbers you want to analyze when looking at FPS.

The first is "Extreme Spread (ES)." ES is the difference between the fastest and slowest rounds.

The second, and IMO most important number is "Standard Deviation (SD)." In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean of the set, while a high standard deviation indicates that the values are spread out over a wider range.

The lower the SD, the closer your FPS is shot to shot.

Getting single digit SD's is very doable, I've got a 243 Win load with an SD of 3.5 but I also use an FX120i, anneal cases, use a bushing die, expander mandrel, etc. Point is you can get that number as low as you want but it is usually related to spending more money.

 

[N2TRKYS]

I’m getting single digit SD and ES in the teens in all my cartridges. I’m using regular RCBS dies, full length size, and don’t anneal cases.

I wouldn’t settle for 50, even in hunting loads, but that’s just me.

 

[Brendan]

It depends what your goal is and what ranges you'll be shooting.

If you're 500 yards and under, an ES of 50 won't matter at all. That's plus or minus 25 fps, which equates to less than an inch difference (my rifle / load) at 500 yards.

At 1000 Yards, that grows to ~6" of vertical dispersion. And continues to go up from there.

Personally, I'm chasing ES in the teens for all my loads because I like tweaking for the "best" load possible.

 

[aron]

What type of chronograph are you using? I've had less than stellar luck with shooting chrony and the accuracy/variation from that alone.

 

[HuntBG84]

What type of chronograph are you using? I've had less than stellar luck with shooting chrony and the accuracy/variation from that alone.

I am using a Caldwell ballistic precision chronograph. Manufacturer number 720001.


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[HuntBG84]

It depends what your goal is and what ranges you'll be shooting.

If you're 500 yards and under, an ES of 50 won't matter at all. That's plus or minus 25 fps, which equates to less than an inch difference (my rifle / load) at 500 yards.

At 1000 Yards, that grows to ~6" of vertical dispersion. And continues to go up from there.

Personally, I'm chasing ES in the teens for all my loads because I like tweaking for the "best" load possible.

What are you tweaking when you are chasing teens?


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[tdhanses]

I personally want ES 25 or lower with a single digit SD.

 

[Brendan]

What are you tweaking when you are chasing teens?


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Powder charge, potentially powder type, seating depth, primer type, neck tension, brass prep methods. Lots of things - Shawn Carlock from Defensive Edge put up a good "Send It" video recently dealing with ES.

 

[HuntBG84]

Powder charge, potentially powder type, seating depth, primer type, neck tension, brass prep methods. Lots of things - Shawn Carlock from Defensive Edge put up a good "Send It" video recently dealing with ES.

I will check it out. Thank you!


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[Brendan]

I will check it out. Thank you!

Found it. Pretty good start here, but this can be a rabbit hole you get stuck going down. Just remember the practical side, really doesn't matter in most situations. (Yet, here I am going through it right now prepping brass for testing this coming weekend...)

 

[HuntBG84]

Found it. Pretty good start here, but this can be a rabbit hole you get stuck going down. Just remember the practical side, really doesn't matter in most situations. (Yet, here I am going through it right now prepping brass for testing this coming weekend...)

This is exactly what I needed. Thanks again for the information.


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[fraz01]

All good info on the video. I'm working up a load in a 30-06 AI. Using two brands of brass and two brands of primers. One of the primers is consistently running 10 to 12 fps faster and 20 fps more Es in both brands of cases. Single digit ES is usually attainable with all the great components available today.

 

[N2TRKYS]

Found it. Pretty good start here, but this can be a rabbit hole you get stuck going down. Just remember the practical side, really doesn't matter in most situations. (Yet, here I am going through it right now prepping brass for testing this coming weekend...)

Lol. Trimming brass is about the only thing that I do that he talks about.

 

[Brendan]

Lol. Trimming brass is about the only thing that I do that he talks about.

I definitely don't do everything he does, and do some things he doesn't (e.g. Annealing). But, definitely has merit. A lot of his shooting is ELR shooting with big magnums - .338 Terminators, etc. where ES really matters at those extended ranges.

Also, while my 6.5 CM has been EASY to get ES in the teens, my 300 Win Mag not as much. My initial guess is as powder capacity goes up the potential for velocity variation goes up with it.

 

[N2TRKYS]

I definitely don't do everything he does, and do some things he doesn't (e.g. Annealing). But, definitely has merit. A lot of his shooting is ELR shooting with big magnums - .338 Terminators, etc. where ES really matters at those extended ranges.

Also, while my 6.5 CM has been EASY to get ES in the teens, my 300 Win Mag not as much. My initial guess is as powder capacity goes up the potential for velocity variation goes up with it.

It can definitely leave you scratching your head. Especially, if the experts contradict each other or it doesn’t mirror your experience at all.

You just have to do what works for you.

 

[FLS]

Low ES/ SD comes from consistency. It’s a combo of good brass, good brass prep, neck tension and consistent powder charge, in a good barrel.
For my match rifle I full length size Lapua brass, moving the shoulder back .002, expand the neck with a carbide mandrel, charge using a Chargemaster, and seat with a micrometer seating die. I have a buddy anneal my brass ever 3-4 loads.
Over a 20 shot string my SD/ ES is single digits.
That’s out of a Kreiger barrel chambered by a riflemsmith that’s a perfectionist.
I’ve have some factory hunting rifles that I can’t get single digits with. More generous chambers and long throats. I’m happy with ES in the mid teens.
FWIW, I don’t think you need a powder dispenser that measures to the .001 grain and I don’t think need to anneal unless your trying to maximize the number of reloadings you get on your brass. You’ll feel the amount of seating pressure change as the necks get harder. When that happens your SD/ES is getting larger.

 

[Jaden Bales]

There are two numbers you want to analyze when looking at FPS.

The first is "Extreme Spread (ES)." ES is the difference between the fastest and slowest rounds.

The second, and IMO most important number is "Standard Deviation (SD)." In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean of the set, while a high standard deviation indicates that the values are spread out over a wider range.

The lower the SD, the closer your FPS is shot to shot.

Getting single digit SD's is very doable, I've got a 243 Win load with an SD of 3.5 but I also use an FX120i, anneal cases, use a bushing die, expander mandrel, etc. Point is you can get that number as low as you want but it is usually related to spending more money.

Pretty sure I'm going to save this explanation for my kids when they learn about standard deviation in school. This would have made me WAY more interested in that math class. Haha.

 

[mvrk28]

Pretty sure I'm going to save this explanation for my kids when they learn about standard deviation in school. This would have made me WAY more interested in that math class. Haha.

HAHA

Full disclosure I did some googling and posted the best explanation I saw. But I think your point holds true, taking your kids to the range can now be called homework for their probability and statistics class. Kids will always wonder why their dad pushes them so hard to take that course.