Muzzle velocity versus accuracy?

[Shootfish]

Does the velocity of a pellet affect the accuracy? If two identical airguns (speaking theoretically, as I appreciate it is extremely difficult to get two identical airguns) are producing the same velocity at the muzzle, and you then lengthen the barrel of one which produces greater velocity, does that increase in velocity make that gun inherently more accurate?

[Phil Russell]

My opinion: short answer 'No'.
But, the increased velocity may make the pellet less influenced by external factors due to shorter flight time e.g. wind. But that is not what you were asking.
Just think of the Theoben gas rams with 7" barrels. Accuracy was excellent.
Cheers, Phil

[Artfull-Bodger]

You need to define accuracy here, A higher velocity will create a flatter trajectory leading to less holdover or the requirement to learn the ballistic arc, (think .177 vs .25) but does higher velocity mean tighter groups? no.

In fact there is a practical limit for the shuttlecock pellet shape before velocity and rotation leads to instability, heres a good example of such a problem occurring from overspeed - https://www.youtube.com/watch?v=QFou_4VqLBY

[clunge]

Rather than lengthening the barrel - which is a rather impractical option if you are comparing identical guns - it would be easier to use one gun with an adjustable regulator and/or hammer spring, such as an FX Impact (other adjustable guns are available).

Then you could plot a graph of group size against velocity.

I think this is exactly what Ted ('s Holdover) Bier did, before winning the 2016 Extreme Bench Rest.

Edit: In fact he's just put up a couple of new vids explaining how. I'm off to watch 'em.

Edit 2: Just watched both modest little vids :-) and the mechanics of how he tuned the velocity of the impact is yet to come :-(

[Shootfish]

So a higher velocity, getting from muzzle to target quicker, will mean the pellet spends less time in the air and could be affected less by external influences. Ok, so theoretically, would the grouping therefore stay the same until a velocity is reached where the pellet becomes unstable?

NB Thanks for the heads up on Ted Bier; he makes a lot of sense.

[Artfull-Bodger]

So a higher velocity, getting from muzzle to target quicker, will mean the pellet spends less time in the air and could be affected less by external influences. Ok, so theoretically, would the grouping therefore stay the same until a velocity is reached where the pellet becomes unstable?

oooh I detect a holy grail hunt coming on

If your talking about adding 10 or 20fps it's likely you will see no difference whatsoever.

Here's the conundrum, we are limited to 12ftlbs, so velocity is directly related to weight as if you wish to go faster within this limit then your only recourse is going lighter on the pellet!

Theoretically the lighter the pellet the more it could be deflected by a given wind speed, but, if it's in the air for a shorter period then the wind has less time to affect the flight path, so again theoretically there should be a crossover point between the weight and velocity where optimum grouping could occur!

If you find it let us all know

Lets chuck a bit of anecdotal evidence into the mix, I shoot with Falcon Accuracy 7.3 grain in my springers, except my HW77FT, through that I put Express 7.9g, the Falcons group just as well as the Express but I have more confidence in the Express to use it in a competition as I believe they will be affected by wind less and they produce superior groups to 8.44 in my rifles, I can't prove that as I have never shot each pellets side by side in the same wind to find out, going to have to try that actually, So I am hedging my bets by going for the best grouping pellet with the flattest trajectory with what I hope is the least wind deflection within those parameters.

Put another way I'm hoping rather than knowing, only testing will settle this matter.

One thing I have settled on is the lighter 7.9 or 7.3 pellets in .177 because they produce better results than 8.44 or heavier, I have found no advantage to going for heavy pellets, the trajectory negating any theoretical advantage they may have, but they may well deflect less in wind, however the excessive drop means for me they are of no practical value.

[Shootfish]

oooh I detect a holy grail hunt coming on

If your talking about adding 10 or 20fps it's likely you will see no difference whatsoever.

Here's the conundrum, we are limited to 12ftlbs, so velocity is directly related to weight as if you wish to go faster within this limit then your only recourse is going lighter on the pellet!

Theoretically the lighter the pellet the more it could be deflected by a given wind speed, but, if it's in the air for a shorter period then the wind has less time to affect the flight path, so again theoretically there should be a crossover point between the weight and velocity where optimum grouping could occur!

If you find it let us all know

I'm afraid I have no recourse to a practical application; having almost fulfilled my collection, I am now keen to learn the theories behind airgun operation and what things affect different parameters of shooting. I had to start somewhere, and I started reading about the myth that 'longer barrels mean better accuracy'. I am only a plinker (spelt with an 'i') but I guess that competitive shooters have asked all these questions before.
Thanks all, for your inputs.

[TORNADOS7]

From personal experience I'd say yes but as has been said whether the higher or lower velocity to a greater or lesser extent is effected by atmospherics well who knows...

All I know is I've shot a rifle at say 10fpe and it's been grouping reasonably well and then shot same rifle at 11.4/5 and the grouping has either improved, got worse or stayed the same...

I know my 'TX200hc' shoots better at higher velocities with some pellets and worse with others, so how much of an effect is the pellet having...��

[clunge]

Ok, so theoretically, would the grouping therefore stay the same until a velocity is reached where the pellet becomes unstable?

Apparently not.

For a given pellet, in still conditions, group size is said to shrink with increased velocity until a velocity (which varies from pellet to pellet) is reached where the group size starts to increase.

For diabolo pellets, this velocity may, or may not, be in the region of 900fps.

In order to keep on thread (talking just about the relationship between velocity and group size) I'm ignoring stuff like trajectory (loopiness) and crosswind.

[lensman57]

Does the velocity of a pellet affect the accuracy? If two identical airguns (speaking theoretically, as I appreciate it is extremely difficult to get two identical airguns) are producing the same velocity at the muzzle, and you then lengthen the barrel of one which produces greater velocity, does that increase in velocity make that gun inherently more accurate?

Yes to a degree. Given the inherently odd shape of an air rifle projectile, there is a finte speed beyond which aerodynamic instability sets in.
If the barrel is well contsructed you will see no instability up to 930~950 ft/s for Diabolo design pellets, perhaps slightly higher for the quasi bullet shaped ones.
Faster projectile means flatter trajectory in a comparable distance to a slow pellet ( within a specified kill zone ) and this aids in " accuracy ".
There are other factors involved if you were hunting but as a whole the answer is yes.

A.G

[bucketboy]

It depends on barrel/pellet compatibility, +or- 10 fits can make a big difference to the accuracy, faster is not always better, slight imperfection of the pellet will be exaggerated at higher speeds. From my experience I found heavier larger cals are more suited to high speeds more that smaller lighter pellets.

[ballisticboy]

First I assume by accuracy you are talking about group size which is actually dispersion in the UK, accuracy is the distance of the group center from the point of aim as was pointed out earlier and almost certainly would improve with velocity. Dispersion though is much more complicated.
The method used to increase the velocity will have an effect on the dispersion as well as the pellet itself. For example, if you do as you suggest and increase the velocity by lengthening the barrel (presumably on a PCP as doing it on a springer could well reduce the velocity) then as the pellet leaves the barrel the air pressure behind the pellet will be lower which may well reduce the disturbance on the pellet giving smaller dispersion. However, if the majority of your dispersion is due to the pellet having a slightly off center CofG then increasing the velocity could make the dispersion worse. Producing the increase in velocity by changing the amount of air with an adjustable regulator would also increase the air pressure when the pellet leaves the barrel and could well give an increase in dispersion size.
There will come a point when the pellet begins to encounter dynamic stability problems (not gyroscopic or aerodynamic stability) as it moves down range which will lead to an increase in dispersion. This point will vary depending on the pellet and the gun but is normally around the 900-950 ft/sec point. The effects mentioned above could well have begun to increase dispersion well before you reach this point.
In addition to the pellet effects there can be other interactions between the pellet and barrel which are affected by the pellet exit time leading to changes in pellet yaw and thus dispersion size. Again, the velocity effects will be dependent on the exact pellet barrel combination being used.
So there is no simple answer to your question as it will depend on the particular pellet gun combination you are using.