Long range airgun shooting

[RichardH]

Richard, there is one thing that you don't seem to have taken into account and that's the different stabilisation methods of pellets versus bullets.

Pellets are by and large (boat-tailed bullet type designs) have drag stabilisation as a large component of the total stabilisation (as the Cardews showed). Spin does come into it or we'd all be shooting smooth bores but drag stabilisation is very important. Needless to say I'd expect that to be a significant factor in the differences between a bullet and a diablo shaped pellet.

The effect of the different shapes on the wind's effects has got to be a factor too.

I don't think you can compare pellets to bullets. Especially when the bullets are being shoved along at 4000 fps!

Hi Weevie

All fair points, however if a drag stabilised diablo will stay stable at 550fps at 50 yards from a legal limit gun, what physical condition would cause it to become unstable from an FAC gun giving say 550fps at 100 yards?

As long as you stay inside the speed of sound then I cant see a reason (that translates across from firearms where much more is written) why it would suddenly deviate from its planned course.

Now to increase BC it may be necessary to move to longer heavier projectiles which may (or may not) benefit from a faster rifling twist?

I think the answers here may well be along different lines to what's accepted at 50 yards, for example three combinations shooting 1/2" groups at 50 yards may very well produce wildly differing groups at 100 much as with rifle cartridges.

I dont have the answer but I'm sure it doesn't reside with any one individual messiah more a reasoned (or lucky) choice of rifle and projectile in optimum conditions which will probably take much experimentation.

That said unless anyone can explain how a 550fps airgun pellet can become suddenly wildly unstable past a certain distance regardless of the speed at which it was launched I can only conclude a 1" group at 100 must be possible with the right barrel, twist and projectile.

If anyone has this information please let me know and save me hours of agonising

Richard

[bengarzy]

Now I'm puzzled Terry

I think we can agree that:

1- A MOA hold is easily acheiveable from a bench?
2- A modern pre-charged legal limit gun can pull 1/2" groups at 50 yards (MOA)
3- There is no wind indoors
4- A modern FAC airgun can produce twice the legal limit in terms of energy easily

What ballistically therefore can cause a previously stable pellet from a 24ft/ib rifle to be unstable at 100 when a legal limit rifle at half the power is very stable at 50?

Is it a function of needing faster twist rates for heavier pellets?

In short why are you convinced its impossible when physics dictates it has to be?

Richard

It might have twice the energy but its not going twice as fast (which wouldnt help accuracy much as the projectile is not bullet shaped) so you are stuck with the projectile dfference between your centre fire rifle and Harry's pair of very ordinary (on paper) PCPs for comparison.
I didnt believe his claims when he got so much of the "down range energy" and other associated facts so wrong from what Terry and I and 2 others found some years back now and he would never answer those questions .

Ben

[baz]

This thread is now in its own section

[Born Again]

Another point, does anyone have a formula to calculate how much wind effect on a pellet/bullet will be decreased at 4000ft ? It must have less effect, the air is much less dense.

[bengarzy]

150 yards is ambitious to say the least, I suspect reality is close to 100 but physics dictates it must be possible unless theres an evil vortex that applies to airgun pellets once they pass the magic 50 yards.

To shoot heavier bullets in centrefire calibres its standard practice to up the twist rate from 1/12 or 1/14 to 1/8 or 1/7 now given I would expect a heavy pellet to be essential to acheiving this why wouldnt this apply to airguns too?

By increasing the weight of the bullet from 55 to 80 grains and the twist rate from 1/12 to 1/7 a .223 rifle goes from a 300 yard gun to one with potential past 600.

Now has anyone got an airgun with a fast twist barrel?

Richard

Could be something in this Richard, all air rifle barrels are around 1in16 and that that dates back from when they were making 0nly 500-600 ft ps in either calibre, I will have to try some stuff to see if the elevated speeds we now use could benefit from a different twist rate.

Ben

[Gary C]

Another point, does anyone have a formula to calculate how much wind effect on a pellet/bullet will be decreased at 4000ft ? It must have less effect, the air is much less dense.

Wind at altitude has a slight effect too...

[bengarzy]

Richard

Shooting bullet type projectiles or waisted JSB pellets like Harry

Ben

[Born Again]

Wind at altitude has a slight effect too...

I know it will have an effect, but the effect must be reduced. If we know by how much the effect is reduced we can apply a fudge factor to our group sizes to see if we can match Harrys.

[RichardH]

Could be something in this Richard, all air rifle barrels are around 1in16 and that that dates back from when they were making 0nly 500-600 ft ps in either calibre, I will have to try some stuff to see if the elevated speeds we now use could benefit from a different twist rate.

Ben

I can only speak from powder burners Ben.

But we do shoot heavier projectiles much faster these days and the way forward here has been long proven to be faster twist rates in firearms.

Airguns may be entirely different but it would seem worth trying, who knows even Bobs air bullets might work with a fast twist

Richard

[Harry's Lad]

He did the same with me when I asked where he got his pellet wheights from and his energy at 100 and 150 yards with the JSB he was useing as it was about 70% up on reality.

I’m guessing that Harry used the energy estimates (at 100 and 150 yards) from ChairGun2. He would be confident in using these since, paying meticulous attention to detail, he has already checked velocities at those ranges and is more than capable of conducting the simple calculation. I seem to remember that he mentioned (in the withdrawn thread) that he bulk-weighed the pellets – if you’re measuring velocity then the effect of tiny fluctuations of mass on the downrange energy equation are equally tiny. The effect on the trajectory is also tiny.
You also need to consider that, at 4000 Ft elevation, the BC value of a JSB pellet is enhanced so that the downrange energy retention is also enhanced. Where does this “about 70% up on reality” come from?

I didnt believe his claims when he got so much of the "down range energy" and other associated facts so wrong from what Terry and I and 2 others found some years back now and he would never answer those questions .
Ben

Please post these results. I’m sure we’d all like to see them. The ChairGun results (as quoted by Harry) seem pretty close to reality - and to Newtonian physics as we understand it. Perhaps you’ve discovered an anomaly in the time-space continuum …

Another point, does anyone have a formula to calculate how much wind effect on a pellet/bullet will be decreased at 4000ft ? It must have less effect, the air is much less dense.

The altitude is already (indirectly) accounted for. The generally accepted ‘Rifleman’s Formula’ – as used in ChairGun and everywhere else as far as I can see – postulates that deflection is proportional to the difference between time-to-target in air and time-to-target in a vacuum. In a vacuum the BC value is infinite but the BC value experienced in air depends primarily on the air density (which is, in itself, a function of air temperature and pressure). At elevation, the air density is reduced … so the BC value is increased (less drag) … so the time-to-target is reduced … hence the wind-drift is proportionately reduced.

Clear as mud, eh?

Dave

[bigtime]

is it that gary/terry/and ben can not do it so it must not be true and no one else can do it maybee thats why harrys thread was deleted

[Born Again]

The altitude is already (indirectly) accounted for. The generally accepted ‘Rifleman’s Formula’ – as used in ChairGun and everywhere else as far as I can see – postulates that deflection is proportional to the difference between time-to-target in air and time-to-target in a vacuum. In a vacuum the BC value is infinite but the BC value experienced in air depends primarily on the air density (which is, in itself, a function of air temperature and pressure). At elevation, the air density is reduced … so the BC value is increased (less drag) … so the time-to-target is reduced … hence the wind-drift is proportionately reduced.

Clear as mud, eh?

Dave

I'll confess to not understanding this "time difference" theory at all. If there was a formula relating side-on BC, wind speed and flight time I could understand it, but what on earth does the flight time in a vacuum have to do with it

[RichardH]

Stop it, somewhere in here is a sensible discussion

[baz]

is it that gary/terry/and ben can not do it so it must not be true and no one else can do it maybee thats why harrys thread was deleted

Maybe Harry cant do it in front of someone

You have been told several times why Harry was deleted, I suggest you go back and read them

[bengarzy]

From being someone that wanted to hear more about all this, I've now lost the will to live! Maybe I should go and lie down, could be a good idea anyway, as I wrote off the Range Rover today.

Best thing that ever happened to it Graham, they were crap when they were brand new......

Ben