Velocity and accuracy?

Others may have different views, but this is my perspective:

• You need to be able to stabilize the bullet. Speed has a marginally positive impact on spin stabilization (faster velocity = faster spin), so for particularly long bullets and slow-twist barrels, you may see a threshold below which accuracy is poor.
• You probably need to get reliable/consistent ignition of powder in order to get consistent results; for some loads/powders, this may mean that you have another threshold below which accuracy is reduced.
• Transonic flight is tough on accuracy. The axiom is that you want to either start supersonic and stay supersonic to impact, or start subsonic and stay subsonic. In many contexts, it's easier with 9mm to simply start-and-stay subsonic. So, in many cases, there may be an upper threshold above which accuracy degrades.
• Other than that, the factors specific to the gun (barrel unlocking timing, harmonics, muzzle/crown condition) are likely to control. Some guns may like an X bullet/Y powder combination driven at 875fps, while another likes the same combo better at 1000fps.
• Separate and apart from purely mechanical accuracy, most people will shoot lower-recoiling rounds more accurately. That's why bullsesye shooters shoot things like 38 special wadcutters and 185 grain .45's, each loaded to pretty light levels.

Many find the most accurate load to be closer to the min load than the max charge with handgun cartridges.

ATL Dave is correct. I have worked up loads where accuracy was best well below max.

I have also worked up loads where accuracy was best at absolute full throttle plus.

IME, many factors effect accuracy. Velocity alone does not directly effect accuracy unless one or more of the other factors is in play.

Every gun is like a woman. You won't find two of them alike. A load that one gun likes may be a complete dud in another identical gun. That is when the fun begins.

Shinbone said:

especially 9mm, is there a correlation between velocity and accuracy generally speaking for any given bullet weight? Is a faster muzzle velocity more accurate that a slower muzzle velocity?

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No, as accuracy depends on several reloading and firearm variables, particularly the barrel.

Captcurt said:

Every gun is like a woman. You won't find two of them alike. A load that one gun likes may be a complete dud in another identical gun. That is when the fun begins.

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Even guns from same manufacture can have varying groove diameter barrels as one THR member experienced poor accuracy with a new 9mm pistol that turned out to have .357"+ barrel. After some hassle with customer service and my insistence, manufacturer provided replacement barrel with groove diameter closer to .355" and accuracy was restored.

ATLDave said:

You probably need to get reliable/consistent ignition of powder in order to get consistent results; for some loads/powders, this may mean that you have another threshold below which accuracy is reduced.

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I agree. In theory, powder charge threshold where more efficient powder burn that produces more consistent chamber pressures should result in more consistent muzzle velocities to produce smaller SD numbers and thus smaller groups on target.

Livin_Cincy said:

Many find the most accurate load to be closer to the min load than the max charge with handgun cartridges.

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Based on my experience and postings of many, this is not the case. And while we have theory of lower SD number loads "should" produce smaller shot groups, this also is not the case.

With auto loading pistols, when the round is stripped from the magazine and slammed against the feed ramp and chambered, we mostly have "powder forward" situation where most of powder charge is away from primer when the firing pin/striker ignites the primer:

• With minimum/starting powder charge, there is more "air gap" between primer and powder charge and powder burn may be less consistent.
• Different powders behave differently with "powder forward" ignition (Just ask Walkalong)
• Powder burning top down instead of primer towards bullet base may contribute/cause incomplete sealing of case mouth with chamber and blow gas down one side of case (I am sure you have seen brass with black soot on one side)
• With minimum/starting powder charge, initial pressure build may not be consistent enough to produce consistent average peak chamber pressures
• Inconsistent chamber pressures will result in less consistent muzzle velocities
• Less consistent muzzle velocities will likely produce greater spread on target thus larger shot group size which we correlate to being less accurate

During load development and powder work up with longest working OAL/COL, I initially look for powder charge that will reliably cycle the slide and produce accuracy as this is the start of "Target load" formation which results from efficient enough powder burn and consistent enough chamber pressures to produce smaller shot group. Then I incrementally increase powder charge towards max load data to look for powder charge that will produce smallest group. Then I incrementally decrease the OAL (which increases deeper bullet seating depth and greater neck tension from thicker case wall) to see if group size decreases.

If group size decreases, I am improving initial pressure build from more efficient powder burn that results more consistent chamber pressures. Depending on powder/burn rate, smallest groups are generally produced by mid-to-high range/near max load data but usually not at minimum/start-to-low range load data.

So greater accuracy may not result from higher powder charge/higher velocity rather high enough powder charge to allow granules to cover the primer when chambered. This may explain why using shorter OAL (With deeper bullet seating depth) and certain powder charge produce smaller groups.

BTW, from my 25/50 yard 9mm carbine testing, 100% case fill load has produced smaller groups than less case fill loads (I know, another Myth Busting thread coming ).

I don't load for handgun rounds, but I found best accuracy at, or very near, the max load listed for all of my rifle cartridges. It really depends on the powder. You want to fill the case so that the powder has no room to move around inside as the ammo is moved in different positions. If it does you get inconsistent ignition and less accuracy. Some powders will be at a max load and still leave lots of room in the case for the powder to move around. Other powders will completely fill the case at or near max charges.

I think that some guys shoot more accurately with loads near minimum because they are getting less recoil. Not because the load is more accurate.

There is no compelling evidence that consistent velocity is correlated with accuracy in the usual pistol at usual pistol distance, i.e. 25 yards. See the article here:

https://americanhandgunner.com/exclusive-consistent-velocity-accuracy/

yes. yes.

greater velocity, all else being equal (except the powder charge, of course), means less time the bullet spends in the barrel. less time means the shooter has less time to screw up the shot with the movements it takes to make the shot before the bullet exits the barrel.

this wouldn't apply to using a ransom rest since the ransom rest supposedly takes the shooter, and all the shooters inconsistencies, out of the shooting process.

there are a lot of other variables that affect accuracy, so this probably gets lost in the noise of variability and goes mostly unnoticed.

if the shooter is consistent enough, the velocity won't matter, so the bullseye shooter will go with the softer load every time.

luck,

murf

If the gun was still when the cartridge ignited, I think it improbable that a handgun shooter could accelerate the gun rapidly enough to materially impact accuracy. The bullet "dwell time" after ignition is a fraction of the "lock time" it takes the hammer to fall/striker to strike. That's not where human-introduced inaccuracy comes from. It comes from not having the barrel pointed directly at the target at the moment the sear breaks. The low-and-left flinch pattern comes from a muzzle dive that happens before the gun goes off, for instance.

yes. yes.

greater velocity, all else being equal (except the powder charge, of course), means less time the bullet spends in the barrel. less time means the shooter has less time to screw up the shot with the movements it takes to make the shot before the bullet exits the barrel.

this wouldn't apply to using a ransom rest since the ransom rest supposedly takes the shooter, and all the shooters inconsistencies, out of the shooting process.

there are a lot of other variables that affect accuracy, so this probably gets lost in the noise of variability and goes mostly unnoticed.

if the shooter is consistent enough, the velocity won't matter, so the bullseye shooter will go with the softer load every time.

luck,

murf

ATLDave said:

If the gun was still when the cartridge ignited, I think it improbable that a handgun shooter could accelerate the gun rapidly enough to materially impact accuracy. The bullet "dwell time" after ignition is a fraction of the "lock time" it takes the hammer to fall/striker to strike. That's not where human-introduced inaccuracy comes from. It comes from not having the barrel pointed directly at the target at the moment the sear breaks. The low-and-left flinch pattern comes from a muzzle dive that happens before the gun goes off, for instance.

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i don't think the shooter can hold a handgun perfectly still. and it doesn't take much movement to have a material affect on the bullet trajectory and accuracy. experienced shooters strive to keep the sights aligned and the shot process the same. any slight inconsistency shows up at the target. and a greater velocity means less time for the inconsistencies to affect the shot.

i'm not saying the velocity increase affects accuracy a lot, i'm just saying it does affect accuracy. there are a bunch more things in the shot process that affect accuracy much more than this; inconsistent grip pressure is a biggie.

murf

murf said:

i don't think the shooter can hold a handgun perfectly still. and it doesn't take much movement to have a material affect on the bullet trajectory and accuracy. experienced shooters strive to keep the sights aligned and the shot process the same. any slight inconsistency shows up at the target. and a greater velocity means less time for the inconsistencies to affect the shot.

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You seem to be assuming that, although shooters cannot hold the pistol perfectly still, their aim at the moment of ignition is perfect and degrades from there. And that the infinitesimal difference in dwell time between a bullet leaving the barrel at say, 1000 fps versus one leaving the barrel at 800 fps, has a consistently negative consequence as a result.

These seem extremely unlikely to me.

the reduced barrel time reduces all inconsistencies no matter how small. the reduction may be inconsequential for most shooters, but exists non the less. imhsa shooters and hunters probably benefit from this the most as they shoot handguns at long ranges.

murf

I have never seen any correlation between velocity and accuracy.

Many hand loaders will tell you that the most accurate loads are always a grain or two below maximum.

I have not found this to be true. Sometimes it is, many times it isn't.

maybe between a tc encore and a blackhawk both with ten inch barrels? the blackhawk shooting 357 magnum, the encore shooting 7mm tcu? the velocity difference has to be large to be noticed, i think.

murf

murf said:

the reduced barrel time reduces all inconsistencies no matter how small. the reduction may be inconsequential for most shooters, but exists non the less. imhsa shooters and hunters probably benefit from this the most as they shoot handguns at long ranges.

murf

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murf said:

maybe between a tc encore and a blackhawk both with ten inch barrels? the blackhawk shooting 357 magnum, the encore shooting 7mm tcu? the velocity difference has to be large to be noticed, i think.

murf

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How much difference does it make? How much of a velocity difference is required for there to be a meaningful difference?

The hypotheticals are fine, but if you do the actual math and find out that at most there is a 0.10" change in point of impact and the gun is only shooting a average 2.0" group at 25 yards anyway, with a range of +/- 1.5" group sizes (i.e. range from 0.5" to 3.5" group size), then why should we care?

shinbone asked:
...is there a correlation between velocity and accuracy...

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No.

There are simply too many other factors in play. The gun, the load, the gun, the shooter, the technique; well, you get the idea. With any new load, begin with the Starting Load and work up incrementally from there.

Maybe the question should be rephrased. Is there a correlation between velocity and accuracy - when the gun is fired from a Ransom Rest or when fired with the barrel in a barrel fixture.

Including the human in the equation adds a variable that that throws accuracy out the window. Adding the human asks a question about the skill of the shooter that can destroy any and all mechanical accuracy.

Let's keep the human out and ask a simple question about the relationship between velocity and accuracy. Period. The answer to this question gets to the heart of accuracy.

Maybe,
I loaded one round with a primer only and since the bullet velocity was 0 at the muzzle it was not accurate at all.

In rifle rounds there is the issue of barrel harmonics where a small change in velocity can affect accuracy, I would assume you would see the same thing in pistols as well.

For whatever reason I can say from testing that any one of my pistols might shoot a certain bullet/powder combo better at say 1030fps or better at 1060fps or better at 1000fps,
so for example a .2gr difference in powder charge (or an OAL change) might make a difference.
So slower or faster is not always better it is just a matter of finding what your gun likes.
A load with powder X and bullet A at say 1050fps might shoot better than a load with powder Y and bullet A also at 1050fps.
A load with powder X and bullet A with an OAL of say 1.10 might shoot better than a load with powder X and bullet A with an OAL of 1.08 with the powder charge adjusted to give the same velocity.

Way to many variables IMO to just say velocity makes a difference assuming we are talking about reasonable velocities for the caliber.

Dudedog said:

Maybe,
I loaded one round with a primer only and since the bullet velocity was 0 at the muzzle it was not accurate at all.

In rifle rounds there is the issue of barrel harmonics where a small change in velocity can affect accuracy, I would assume you would see the same thing in pistols as well.

For whatever reason I can say from testing that any one of my pistols might shoot a certain bullet/powder combo better at say 1030fps or better at 1060fps or better at 1000fps,
so for example a .2gr difference in powder charge (or an OAL change) might make a difference.
So slower or faster is not always better it is just a matter of finding what your gun likes.
A load with powder X and bullet a at say 1050fps might shoot better than a load with powder Y and bullet A also at 1050fps.
A load with powder X and bullet A with an OAL of say 1.10 might shoot better than a load with powder X and bullet A with an OAL of 1.08 with the powder charge adjusted to give the same velocity.

Way to many variables IMO to just say velocity makes a difference assuming we are talking about reasonable velocities for the caliber.

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you came at this from a whole different angle. nice!

murf

fxvr5 said:

Maybe the question should be rephrased. Is there a correlation between velocity and accuracy - when the gun is fired from a Ransom Rest or when fired with the barrel in a barrel fixture.

Including the human in the equation adds a variable that that throws accuracy out the window. Adding the human asks a question about the skill of the shooter that can destroy any and all mechanical accuracy.

Let's keep the human out and ask a simple question about the relationship between velocity and accuracy. Period. The answer to this question gets to the heart of accuracy.

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ok, lets say you shoot ten shots @ 1,000 fps and ten shots @ 1,500 fps (same gun, same bullet). both loads have an extreme spread of 15 fps. the higher velocity round will show less variation in trajectories than the slower round (extreme spread/muzzle velocity is 1.5% for the slower round and 1% for the faster round). so the higher velocity round will show a smaller group size. make sense?

murf

fxvr5 said:

How much difference does it make? How much of a velocity difference is required for there to be a meaningful difference?

The hypotheticals are fine, but if you do the actual math and find out that at most there is a 0.10" change in point of impact and the gun is only shooting a average 2.0" group at 25 yards anyway, with a range of +/- 1.5" group sizes (i.e. range from 0.5" to 3.5" group size), then why should we care?

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i think we have to go with hypotheticals here because there are so many other variables affecting accuracy. i agree about "... why should we care?" when talking about normal handgun velocities. but, the question was asked.

murf

murf said:

ok, lets say you shoot ten shots @ 1,000 fps and ten shots @ 1,500 fps (same gun, same bullet). both loads have an extreme spread of 15 fps. the higher velocity round will show less variation in trajectories than the slower round (extreme spread/muzzle velocity is 1.5% for the slower round and 1% for the faster round). so the higher velocity round will show a smaller group size. make sense?

murf

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So faster is always more accurate, according to you.

Do you have the data to support that? And how did you test it?

murf said:

i think we have to go with hypotheticals here because there are so many other variables affecting accuracy. i agree about "... why should we care?" when talking about normal handgun velocities. but, the question was asked.

murf

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Now you're saying there is no correlation? It's immeasurable?

Yes - this is the right forum

No - I've never found any correlation between velocity & accuracy.

Now having said that, I also haven't tried very slow or extra fast loadings.
ie. 38Spl 750- ~900 fps
9mm 900-1100 fps etc., etc.