Deviation in Muzzle Velocity

[Dragoon 45]

What is considered a good deviation in muzzle velocity for BP Cartridges? I.E. deviation from the slowest to fastest shot in a string? The last time I chrono'ed my .40-65 I got a deviation of 26 fps between slowest and fastest.

I have read guys say they get as little as 6-10 fps deviation and some upwards of 50 fps. So what is considered good?

Thank you.

[405]

No need to get into an academic discussion of statistics here. The two most common terms used are "spread" and "standard deviation". The spread is what you described... the difference between the highest and lowest within a string of shots. Standard deviation is different. It is a statistical good odds "bet" that the next shot will be within a "standard deviation" of the average. To mix the two terms and some even throw in "variance" for more confusion! (and I see it fairly often) is misleading!

For example: I go to the range and shoot a string of shots. I record the velocities and calculate the two pieces of data- spread and standard deviation. Depending on the type of load I might expect something like a spread of 30 and a standard deviation of say 5-10. Funny thing is, except at the longer distances, loads that are the most accurate may not show the lowest spread number nor the lowest standard deviation. But, if you shoot and get wacky numbers like spreads of 100-200 and standard deviations of 75-100 .... probably means the load isn't so good.

[Lead Fred]

The lot I tested were about 20, thats the fun of doing ole timey lead slinging

[montana_charlie]

Among those BPCR types who have much to say on the subject, some are mainly shooters and some are mainly talkers. But they seem to agree that 'single digit' Extreme Spread and Standard Deviation numbers is a reachable goal.

I bought a chrony only to be able to know the ES and SD numbers, and I use it (occasionally) when a particular load is looking extra good. I have fired batches of ammo where both numbers stayed below ten.

CM

[Doc Highwall]

As 405 said the lowest ES may not be the most accurate as a low ES has nothing to do with barrel vibrations. Ask some of the top shooters who have a gun that shoots accurate at 1000 yards with low ES what happens if they rest the barrel on the cross sticks in the wrong place what happens to accuracy. Some people get so involved with low ES and load development that they lose sight that what happens at the target is most important, a small group with high ES is better then a large group with low ES. My advise to shooters is get a load that shoots good first and then go out and shoot a lot and learn to read the wind, get zeros,work on your position, see how the light affects your eyes and then try better load development. Also take lots of notes and don't lose them.

[Dragoon 45]

Thank you for the replies. I was just curious what was considered a good spread between high and low in a string of shots. I also was not sure how important that spread was in load development.

[missionary5155]

Good morning
+1 on the "SHOOT ALOT" and take notes.
Mr. Ned Roberts was one of those GOOD RIFLE shote who never had a Chronograph nor any of the other men he shot against and could occassionally best.
I have a CRONY and use it for just one basic thing.. after I find a great shooting load I get an accurate FPS average from my barrel so I can have an idea what it is going to do way out there...

[Don McDowell]

If you're running good blackpowder loads, you should be getting 10fps or less variation from shot to shot.
The past weekend at Alliance Ne.( Jeff F who took 3rd place in the longrange) ran his 110 loads over the chrony with a 2.8 fps variation. And he uses just planejane Goex 1f.

[SharpsShooter]

Some people get so involved with low ES and load development that they lose sight that what happens at the target is most important, a small group with high ES is better then a large group with low ES. My advise to shooters is get a load that shoots good first and then go out and shoot a lot and learn to read the wind, get zeros,work on your position, see how the light affects your eyes and then try better load development. Also take lots of notes and don't lose them.

That says it all right there. I do not own a chrony. If I just have to know what a load is doing , it is only to get a velocity average of five shots, maybe ten shot over a friends. I can use the average to figure trajectory and sight settings to get on target Standard deviation and or extreme spread numbers do not put meat on the table.


SS

[Don McDowell]

Alot depends on the distance being shot as to how important low ES and SD numbers are. If a person isn't shooting much past 200 yds, then wide swings in numbers won't show up as bad as when you get out to 500 yds.
When you start pushing those bullets out past 500 yds a load that'll shoot minute of deer at 100, may not shoot minute of barn at 525. I've had several loads that while they looked good at 1 and 200 yds, close examination showed at 300 the stringing was coming evident, at 500 yds it was pronounced enough keeping 10 on a 4x4 target wasn't a doable thing.

Consistancy is the name of the game for the tight accuracy.

[Larry Gibson]

Alot depends on the distance being shot as to how important low ES and SD numbers are. If a person isn't shooting much past 200 yds, then wide swings in numbers won't show up as bad as when you get out to 500 yds.
When you start pushing those bullets out past 500 yds a load that'll shoot minute of deer at 100, may not shoot minute of barn at 525. I've had several loads that while they looked good at 1 and 200 yds, close examination showed at 300 the stringing was coming evident, at 500 yds it was pronounced enough keeping 10 on a 4x4 target wasn't a doable thing.

Consistancy is the name of the game for the tight accuracy.

Very well said. Group accuracy at 100 and 200 yards is only meaningful at 500 - 1000 yards if the load is also consistent with a low ES. The two (group accuracy and consistency) go hand in hand. My tests with BP loads in the 45/70 replicating the 1873 and 1882 loads for use in TDs shows most 10 shot strings give an ES of 12 -15 fps with SDs of 6 - 9 fps. The accuracy at 100, 200 and longer ranges out to 1000 yards of those loads is very good.

Larry Gibson

[montana_charlie]

I knew that if I waited, others would post remarks showing an appreciation for low ES and SD values...as well as when and why they are desirable.

While it's true that an accurate load for a given rifle must be found through experimentation; and that a chronograph has little value in that search; once the load has been found it must be loaded consistently to have any value at longer ranges.

Obtaining that consistency...or proving you have obtained it...is where the ES and SD numbers come into play.

You may have learned that your Postell bullets will group well when loaded over 65 grains and a .030" wad.
But, if every bullet weighs the same, and each powder charge is weighed (not just every tenth one) and the cases have been sorted by weight, you are reaching the kind of consistency needed for single digit numbers.
Add to that a concerted effort to keep bore condition exactly the same for every shot.

All of these produce the 'muzzle velocity' which the chronograph is supposed to measure..and if the speed doesn't vary, it can only improve the accuracy of a known good load.

Can there be low ES and SD numbers in a load that can't hit a barn? Of course.
If each round is exactly like every other, the numbers will be low. But, if it's a lousy load (for that rifle) it still won't shoot worth a hoot.

Low numbers have nothing to do with barrel harmonics, muzzle jump, wind drift, or lighting conditions. All of those things exist beyond of the muzzle...which is where the chronograph's job ends.

Single digit ES and SD numbers are proof of good management of bore condition, and 'quality' of the reloads...not the suitability of the load they hold.

CM

[Don McDowell]

Larry those are some pretty good numbers in those 3 groove barrels. When you get a load cooking like that in one of those old buggers it sure doesn't take long to figure out why the 45-70 has lasted so well since 18n73.

[45 2.1]

Low numbers have nothing to do with barrel harmonics, muzzle jump, wind drift, or lighting conditions. All of those things exist beyond of the muzzle...which is where the chronograph's job ends. CM

It would seem that barrel harmonics occur behind the muzzle......... unless you have a really unusual rifle.

[SharpsShooter]

It would seem that barrel harmonics occur behind the muzzle......... unless you have a really unusual rifle.

Post-muzzle harmonics only occur in the Asperly Aimless Mk VI model with the inverted, offside cheek piece...everybody knows that

[Multigunner]

What is considered a good deviation in muzzle velocity for BP Cartridges? I.E. deviation from the slowest to fastest shot in a string? The last time I chrono'ed my .40-65 I got a deviation of 26 fps between slowest and fastest.

I have read guys say they get as little as 6-10 fps deviation and some upwards of 50 fps. So what is considered good?

Thank you.

All I can add is that the .40 bottleneck cartridges were known for considtency in velocity, with the .40-80 being a top notch 1000 yard shooter.
Apparently the best 1000 yard groups with the .40-80 weren't surpassed by modern smokeless cartridges until the 1960's.

[montana_charlie]

It would seem that barrel harmonics occur behind the muzzle......... unless you have a really unusual rifle.

They occur throughout the length of the barrel. But, the bullet is unaware of, and not affected by them, until it leaves the muzzle.
However, muzzle velocity is being developed...regardless of what gyrations the barrel is going through.

At the moment of exit the velocity has been established (providing the good or bad ES and SD numbers), and the location of the muzzle at that instant imparts whatever influence there is to be realized from harmonics...or flinching...or an unsteady rest.

Perhaps you can tell us how barrel harmonics affect the consistency of the muzzle velocity in your unusual rifle...

CM

[SharpsShooter]

I'll take this one. MC he did not say that harmonics effected velocity. He simply stated that harmonics occur prior to the muzzle, which is fact.

But, the bullet is unaware of, and not affected by them, until it leaves the muzzle.

Not entirely true MC. Velocity changes within the bore directly effect the intensity of harmonics while the boolit is still in the bore. So velocity does effect where the muzzle is located at the point of exit. All that happened prior to the the muzzle....


SS

[montana_charlie]

I'll take this one. MC he did not say that harmonics effected velocity. He simply stated that harmonics occur prior to the muzzle, which is fact.

His 'simple statement' was in refutation of my 'simple statement' that low ES and SD numbers are not a product of barrel harmonics, etcetera.
Keep his simple statement in the context in which it was couched if you wish to maintain credibility.

Not entirely true MC. Velocity changes within the bore directly effect the intensity of harmonics while the boolit is still in the bore. So velocity does effect where the muzzle is located at the point of exit. All that happened prior to the the muzzle....

Instead of turning my statement backward, tell me how harmonics change velocity...or more to the point...how they change the 'consistency' of the velocity from shot to shot.

After all, 'consistency in velocity' is the context of the discussion...

CM

[felix]

Each synopsis is correct. ... felix