What is a good Standard Deviation for velocity

[btmj]

I reload 6.5mm Creedmoor. I recently tested 3 different batches of reloads (all loaded in either July or August), and fired 7 from each batch. The standard deviation for velocity from all 21 cartridges was 12.4 Ft/sec, with an average of 2636 ft/sec.

Earlier in the year I tested factory match ammo from Hornady and Federal, and I got ~15 ft/sec as a standard deviation.

I don't have a feel for whether or not I should expect less velocity variation. Is this as good as it gets? Reloading for high accuracy is more complicated than I expected. There are a lot of small variables that seem like they may make a small difference, but when I am trying to make a 1.5 inch group at 300 yards, those small differences start to seem important... Note I said "trying to make a 1.5 inch group"... I have not quite done it yet... close, but no cigar...

I would be interested in hearing from anyone who gets less velocity variation than what I am getting.

Thanks...

[std7mag]

Going for 1/2 MOA at 300 is more about the shooter.

I've only had a couple of powders that i wasn't happy with the ES/SD.
I think it's more a case prep issue.

Your readings aren't too bad. I like single digit SD though.

[btmj]

Thanks for your thoughts. You are right about the shooter being the biggest variable.

My best so far is 2 inch group (5 shots) at 300 yards. I have done it 3 times in the last 6 months. A more typical group size is 3 1/2 inch.

[Road_Clam]

Ive tested and documented over 950 test sesions spanning 21 different calibers. Many handloaders get so wrapped up trying to obtain single digit SD's , when per my real world data i see NO correlation between low SD's and high precision. Ive documented .2 MOA at 200 meters and my SD's were in the low to mid 20's, and contrary, ive observed ES's around 10 fps that yielded a 3 MOA outcome . Testing 2000MR in 308 was a powder that consistiently yielded ES's up in the upper 30's , yet my precision was about 1 MOA .

[mehavey]

0.3% (e.g., SD of 10 at 3,000fps) is an excellent consistency
Short accuracy notwithstanding, SDs do come into play at longer ranges.



(BTW, Black Powder cartridge rifles routinely exhibit such consistency.)

[Bart B.]

A velocity spread up to several dozen fps can be caused by inconsistent hold of the rifle to one's shoulder.

As the smallest groups with a given load are the result of most of the variables canceling each other out and the biggest groups happen when some of those variables add up in all directions, which one of several groups best define the system accuracy? Biggest, average or smallest?

[hounddawg]

at 200 yards you would see about .2 in difference in a 168 SMK traveling at 2700 FPS vs one traveling at 2750

at 1000 yards there would be over 11 inches of difference, the farther out you shoot the more the SD counts

[Bart B.]

Originally Posted by hounddawg

at 200 yards you would see about .2 in difference in a 168 SMK traveling at 2700 FPS vs one traveling at 2750

at 1000 yards there would be over 11 inches of difference, the farther out you shoot the more the SD counts

Except when positive compensation for bullet drop caused by slower bullets leaving at higher angles above the LOS caused by muzzle axis vibration makes all bullets strike close to point of aim. This happens when bullets leave on the muzzle axis upswing near it's high point. At about 60% of target range, slower bullets will be highest above the LOS than faster ones.

Some folks put tuning weights on the barrel muzzle to adjust its vibration frequency to compensate for bullet velocity spread. The muzzle axis is vibrating vertically several hundred Hz (cycles per second) as the bullet leaves.

A muzzle velocity spread of 5 fps is easily masked by a 1% spread in bullet BC at 1000 yards.

Check your ballistic math. Mine gives closer to 20 inch vertical spread at 1000 for a 50 fps spread with that bullet.

[hounddawg]

sure thing Bart.

Now maybe you can explain why all of today's precision shooters measure their powder to the milligram and lose sleep over .001 of neck tension, measure case volume and weigh bullets if consistent velocity does not make a difference at long range.

We can all just toss our scales and go back to Lee dippers according to your theory

[RaySendero]

btmj,

A reloading process that keeps the Coefficient of Variation (COV)
below 1/2 percent is good.

[Road_Clam]

Guys, i apologize, i should have been more specific about my SD opinion, within my above post, im speaking strictly from shooting short range. (200-300 yds)

[Bart B.]

Originally Posted by hounddawg

we can all just toss our scales and go back to Lee dippers according to your theory

With the right combination of rifle, barrel, cartridge, primer, powder and bullet...... yes.

It's not a theory. The British proved the physics behind it over a century ago.

Do you think all bullets leave at the same angle?

[old roper]

Might want to read this.

https://sierrabulletsblog.com/2017/0...aluable-is-it/

[Bart B.]

What's the purpose and function of an adjustable weight near the muzzle?

https://sierrabulletsblog.com/2015/0...-barrel-tuner/

[hounddawg]

Love this entire series but staying on topic

https://precisionrifleblog.com/2015/...oes-sd-matter/

also a fan of diminishing returns, SD's are just one tool in the box. Also a fan of Brian Litz and Erik Cortina. Doing things the same way the current pros are doing them just is common sense in my opinion

[Bart B.]

All those tools in the box end up producing groups at 1000 measuring 7 inches and smaller. Which extreme best defines the loads accuracy; smallest or largest?

[hounddawg]

I don't get my bowels in a tizzy over either. I go by the CEP and horizontal and vertical offset to track progress during practice sessions.

To me a good group is one without flyers and has a nice round shape. As far as size of the group the goal is always less than 1 MOA for 20 shots centered on the X. I currently only shoot F class and not benchrest, I leave the worries about small groups to the group BR guys. F class is more like Palma with half size targets. Have you shot any matches since they cut the rings size in half Bart ? Rings are now only 1 MOA with exception of 800 which uses the 1000 target

[Road_Clam]

One of the interesting aspects of my new venture into black powder cartridge rifle is the fact it seems to be very easy to maintain SD's in the single digits. My average SD is about 9. With smokeless i seemed to observe the widest SD's with 2000MR, 800x and IMR4064.

[Bart B.]

Originally Posted by hounddawg

I don't get my bowels in a tizzy over either. I go by the CEP and horizontal and vertical offset to track progress during practice sessions.

To me a good group is one without flyers and has a nice round shape. As far as size of the group the goal is always less than 1 MOA for 20 shots centered on the X. I currently only shoot F class and not benchrest, I leave the worries about small groups to the group BR guys. F class is more like Palma with half size targets. Have you shot any matches since they cut the rings size in half Bart ? Rings are now only 1 MOA with exception of 800 which uses the 1000 target

https://images.app.goo.gl/N2UAudnxAt5bNAWo6

[Bart B.]

Originally Posted by hounddawg

Have you shot any matches since they cut the rings size in half Bart ? Rings are now only 1 MOA with exception of 800 which uses the 1000 target

Yes, hundreds. And when I and a few other Palma Team members developed loads for Sierra's new 155 grain Palma bullet. I shot the high aggregate score across 4 days of long range matches the first time that bullet was used in competition in 1991.

Do you know why the target rings were about halved? It started in the early 1960's.

Here's a plot of two load's 15-shot test groups at 1000 on the USA Palma Team plotting sheet I designed. Inside X-ring is 10 inches.

https://images.app.goo.gl/N2UAudnxAt5bNAWo6

[hounddawg]

I think you have some dates mixed up Bart or are confusing Palma with F class

The ICFRA was not formed until 2002 and the NRA did not make it a official discipline until 2005. The change from a 2 MOA 10 ring to a 1 MOA 10 ring did not happen until 2007

F class started out in Canada during the mid 1990's and was named after George "Farky" Farquharson. JJ Conway and Bill Wylde introduced it into the US

[Bart B.]

I'm referring to NRA's high power match, any and Palma rifle disciplines.

[old roper]

Bart, How come just about everything you post is over 20yrs maybe going on 30yr. Is there anything current like shot this year.

[hounddawg]

Bart the NRA High Power, Palma, and F class are 3 separate disciplines. I have no clue as to Palma or High Power rules or targets but I do know they are not the same as F class and at my age the days of shooting iron sights farther than 50 yards are long gone

[Bart B.]

Originally Posted by old roper

Bart, How come just about everything you post is over 20yrs maybe going on 30yr.

Because little has changed over the years. Cause and effect remain the same. Some records shot decades ago still stand. Check the size of the largest group in current long range aggregate records for several 10-shot groups. Several inches.

Is there anything current like shot this year.

No. Doesn't matter.