cross bows your view

[HillBill]

Upto a point yes. But with air rifles the velocity you can shoot at is dictated by pellet weight. There could be as much as 50 fps difference between the pellet weights available in .22. Pellet choice is dictated by what your barrel likes to chew on. The Logun needs a diet of accupells, as the rifle was designed to shoot this pellet. These are quite light and as such gain more velocity than a 16 gr pellet would. They are also harder, so less deformation is caused during the firing cycle. But i have tried these in other rifles and they just dont work very well. So i suppose the Logun is optimised for that pellet, But it was built to be. Perhaps thats why i can only group at 70 with this rifle and pellet combo.? One thing is for certain. The logun strikes 4" higher than any other rifle i have had at 70 yards. Even with the same power levels and pellets. The logun groups at 70, so do the others, but not as tight, maybe a 3" spread with some of them.

I can understand that if your longer barrel shoots the pellet faster it will spin faster, but if you are limited to 12 foot pounds doesn't that also limit the maximum velocity you can shoot at?

 

[santaman2000]

...Also a longer barrel delays the effects of gravity which impart forces on the pellet the second it leaves the barrel. This may only be a small amount, but at 70 yards with an air rifle the difference is a couple of inches at the POI...

Doing the math, the difference between an 18" barrel to a 24" barrel (in relation to a 70 yard projectile travel) is only .24%

6" = difference (in projectile travel unsupported to target)
70 yards = travel distance = 2520"

6"/2520" = .002380 X 100 = .24%

So assuming an initial pellet drop of 12.75" at 70 yards with an 18" barrel then you should only decrease it by .24%
12.75 X .0024 = .0306" higher POI. Of course this figure only reflects any difference related to reduced effects of gravity due to shorter pellet travel.

 

[HillBill]

Also a longer barrel on an air rifle allows a lower powered blast of air as there is more time for the propellant to propel the pellet. This efficiency does indeed reduce disturbance at the muzzle which can add a touch of wobble to a pellet. That wobble is less apparent at 30 yards than at 70. But as a general rule, especially as far as firearms are concerned then spin rate is directly linked to barrel length.

HOWEVER, assuming two rifles of same muzzle energy with a particular pellet weight, the muzzle velocity must be the same, hence (assuming same rifling) the pellets will have same spin rpm.

 

[nic.]

Upto a point yes. But with air rifles the velocity you can shoot at is dictated by pellet weight. There could be as much as 50 fps difference between the pellet weights available in .22. Pellet choice is dictated by what your barrel likes to chew on. The Logun needs a diet of accupells, as the rifle was designed to shoot this pellet. These are quite light and as such gain more velocity than a 16 gr pellet would. They are also harder, so less deformation is caused during the firing cycle. But i have tried these in other rifles and they just dont work very well. So i suppose the Logun is optimised for that pellet, But it was built to be. Perhaps thats why i can only group at 70 with this rifle and pellet combo.? One thing is for certain. The logun strikes 4" higher than any other rifle i have had at 70 yards. Even with the same power levels and pellets. The logun groups at 70, so do the others, but not as tight, maybe a 3" spread with some of them.

I understand that but you can only compare like with like, I was assuming you were talking about using the same weight pellets when you said a longer barrel would impart more veloicity and hence spin to a pellet than a shorter one. Definately agree that there are pellet / barrel / velocity sweet spots that seems to give greater stability to a pellet. This seems to be born out as you say by decreased drop at range and increased accuracy.
That seems to be the trouble when making comparisons - it is really hard to change just one variable at a time.

I suppose the acid test is that if you did heaven forbid cut your logun down into a carbine and then adjust the valving to bring the velocity back to the previous level would it spin the same pellets at the same rate?

 

[HillBill]

I think it also has a lot to do with how long the pellet is exposed on route to target. A longer barrel over the carbine version would keep the pellet under positive forces ( increasing velocity and having spin imparted) for a fraction longer. This may seem like a miniscule thing, but everything effects accuracy to some degree after it has left the barrel. The sooner a pellet exits the protection of the barrel the sooner the forces which cause inaccuracy can take effect. At 30 yards you wont notice. At 50 you might notice a POI change, at 70 theres more POI change. The longer a pellet is in the air, the greater the effects of gravity, deceleration and reduction of spin.

 

[nic.]

I think it also has a lot to do with how long the pellet is exposed on route to target. A longer barrel over the carbine version would keep the pellet under positive forces ( increasing velocity and having spin imparted) for a fraction longer. This may seem like a miniscule thing, but everything effects accuracy to some degree after it has left the barrel. The sooner a pellet exits the protection of the barrel the sooner the forces which cause inaccuracy can take effect. At 30 yards you wont notice. At 50 you might notice a POI change, at 70 theres more POI change. The longer a pellet is in the air, the greater the effects of gravity, deceleration and reduction of spin.

I assume you aren't talking about reduced distance to the target for a longer barrel? - the range measurement should really start at the end of the barrel, otherwise you could use a 70yard barrel.

Also velocity has to be the same - if not just for my theoretical experiment but for the 12 foot pound legal limit. A longer barrel that makes a pellet go faster could put you over. We are all stuck up against 11.8 or whatever we feel safe with.
However even if the final velocity is the same the acceleration is reduced in a longer barrel; this may treat the pellet more gently which gives a greater stability in this barrel/ pellet combination?

 

[Harvestman]

Wow, this thread has just put me right off air rifles. I haven't got a degree in maths.

Personally, I'd rather have a crossbow...

 

[HillBill]

That doesnt reflect the reality tbh. All i know 100% is that the accupels strike higher by 4" when fired from the logun, than they do when fired from other rifles of equal velocity. This is a consistent occurrence.

Doing the math, the difference between an 18" barrel to a 24" barrel (in relation to a 70 yard projectile travel) is only .24%

6" = difference (in projectile travel unsupported to target)
70 yards = travel distance = 2520"

6"/2520" = .002380 X 100 = .24%

So assuming an initial pellet drop of 12.75" at 70 yards with an 18" barrel then you should only decrease it by .24%
12.75 X .0024 = .0306" higher POI. Of course this figure only reflects any difference related to reduced effects of gravity due to shorter pellet travel.

 

[British Red]

Wow, this thread has just put me right off air rifles. I haven't got a degree in maths.

Personally, I'd rather have a crossbow...

Wait till you get into long range rifle shooting! You need to measure the relative angle between the shooter and the target, account for Earth curvature and on very long shots, the rotation of the Earth

Ballistics is all formulae and a fair bit of trig too - its about the only useful thing I have found for trig

I'm still a baby though - I haven't got into moly coating bullets for lower friction

Its the ultimate in geekery and thinking - any really long range shooter (or more likely his spotter in military circles) has to really get ballistics in a nerdy way.

 

[santaman2000]

That doesnt reflect the reality tbh. All i know 100% is that the accupels strike higher by 4" when fired from the logun, than they do when fired from other rifles of equal velocity. This is a consistent occurrence.

I have no reason to doubt what you say is happening. It's just that I don't believe that it's caused by the shorter travel path (end of barrel to target) There must be another factor causing greater influence.

 

[santaman2000]

Wait till you get into long range rifle shooting! You need to measure the relative angle between the shooter and the target, account for Earth curvature and on very long shots, the rotation of the Earth

Ballistics is all formulae and a fair bit of trig too - its about the only useful thing I have found for trig

I'm still a baby though - I haven't got into moly coating bullets for lower friction

Its the ultimate in geekery and thinking...

I'm waiting for the first rail gun to hit the civilian market.

 

[HillBill]

Fair enough mate.

Theres not much to go on really other than barrel length. As it is the only thing that i can see making a difference. I've measured FPS every 5 yards to target with a chrono, all the rifles show a consistent rate of drop off upto 55 yards. At 55+ the shorter barrelled rifles seem to drop off much more than the logun. Its at this point where the accuracy starts to suffer for them, where as the logun keeps grouping. Hence my idea that the pellets are de-stabilising in flight

I have no reason to doubt what you say is happening. It's just that I don't believe that it's caused by the shorter travel path (end of barrel to target) There must be another factor causing greater influence.

 

[Chiseller]

Wait till you get into long range rifle shooting! You need to measure the relative angle between the shooter and the target, account for Earth curvature and on very long shots, the rotation of the Earth

Ballistics is all formulae and a fair bit of trig too - its about the only useful thing I have found for trig

I'm still a baby though - I haven't got into moly coating bullets for lower friction

Its the ultimate in geekery and thinking - any really long range shooter (or more likely his spotter in military circles) has to really get ballistics in a nerdy way.

Then there is the ground your shooting over... Different ground colours have different thermals... Brown's not greens... Eg, moor n meadow.... An just to Stoke the embers more.... I shot more gear wi my ol theoben fenman. 20 than I have wi any other slug gun....

Lol ignore me fellas, couldn't resist.... I prefer lurcher any road :sly:


Nuggets.. "YOW Bear Yow Bear"
Bear.. "Eyup Chis... Can yor undastand a wurd e just sed? "

 

[British Red]

And air temperature...humidity.....time of day causing thermal expansion or contraction

 

[dwardo]

Or you could all just get closer

 

[British Red]

Rather like hugh jumpers really - why not just make the bar lower?

 

[dwardo]

Rather like hugh jumpers really - why not just make the bar lower?

Getting closer is just as much fun, not to mention just as adictive.

 

[HillBill]

Not always possible though.

Getting closer is just as much fun, not to mention just as adictive.

 

[santaman2000]

Getting closer is just as much fun, not to mention just as adictive.

For hunting yes, but we seem to have drifted into long range sport shooting as well. Two separate sports; eack fun in its own right.

 

[H2497]

I think you are misunderstanding what i'm trying to say tbh. All this time i have been talking about air rifles and you are talking about firearms for the most part. No friend – you tried to support your argument that long barrels are magic by asking why a sniper rifle does not have the same length barrel as an SMG.

Let me try clarify it a bit.

A blast of air from an air rifle is different to the charge used in cf cartridges. Cant compare them in terms of effect. Air has no burn time. You contradict yourself again – what happened to a longer airgun barrel allowing the blast of air to propel the pellet longer? For the purposes of this argument the principals are indeed similar.

What i'm saying with the longer barrel is that as it gives a higher velocity, (Okay, so it’s the starting velocity that is giving you longer range over your other airguns) this will also give it a higher spin rate as spin is relative to velocity. (Okay) The faster it flies the faster it spins.(Yup) The greater the range before it slows down to destabilisation point. Were talking low velocity air rifles here, not CF rifles so get the CF stuff out of your head for a minute. (I have)
At such low velocities the destabilisation point arrives quickly. A 12 ft/lb rifle firing a pellet at a target at 70 yards for example, would only have lets say 6ft/lb of energy left so at a guess lost a third of its velocity, also a third of its spin rate. At 90 yards it will be at around 4 ft/lbs which is to say its lost half of its velocity and half its spin rate.I don't know the exact percentage required to reach de stabilisation as its different for every rifle/pellet/round combo. But at some point around that area the pellet will start to "wobble" and accuracy falls off. (So? Again, same pellet, same rifling, same starting velocity, why is the long barrel more accurate?)

Also a longer barrel delays the effects of gravity which impart forces on the pellet the second it leaves the barrel. This may only be a small amount, but at 70 yards with an air rifle the difference is a couple of inches at the POI. (Jesus wept. This doesn’t deserve a response).

A longer barrel will be more accurate at greater range than a shorter barrel on an air rifle will for the reasons above. Like i said, my other rifles wouldn't attain the same group at that distance. All had shorter barrels. (And lower velocities presumably?)

I never said a bullet will "run out of spin" i said that spin slows in relation to velocity until it reaches a destabilisation point at which a bullet will "tumble" the same thing effects air rifle pellets which aint breaking sound barriers. (So, given the same pellet weight and design, same rifling, its the starting velocity that is important for longer range accuracy?)

Now I see where you have become confused, earlier you said:

“The shorter the barrel of an air rifle, the less spin is imparted on the pellet. Therefore the spin will slow down quicker and the pellet will de-stabilise in flight sooner, you will get wobble from the skirt first which will then deviate the flight path of the pellet. Greater the range, greater the deviation.”

This is not true. If the pellet leaves the rifle at the same velocity the pellet is spinning on its axis at the same rate. A longer barrel, does not in itself spin a pellet more.

"All i know 100% is that the accupels strike higher by 4" when fired from the logun, than they do when fired from other rifles of equal velocity. This is a consistent occurrence."

Your logun could have a twist rate that suits the pellets better than on your other rifles, but its unlikely to make that much difference, if the twist rates were the same then you Logun would appear to be outside the laws of physics. You seem to be saying that a longer barrel can flatten trajectory whilst keeping the velocity the same. You must know that is impossible.