Moderator as barrel tuner

[1066]

37 minutes ago, brown dog said:

Yup, if the Al tube is holding a damping material, to my mind.   

Is that yours?

No that's a commercial one - Not sure how that works but something similar with a dozen "o" rings under it and clamped up should do - in fact just a tidy version of a limbsaver.

[1066]

1 hour ago, terryh said:

....and you tune the barrel length to the MV to find the next batch you buy has a different MV 😨 it must be adjustable IMHO

If you are looking at a bulge wave (sort of reverse peristalsis if you like) could you put a clamp on the barrel (like a scope ring design item) that messes with the bulge wave, a tuner for longitudinal waves as opposed to the barrel end tuner trying the mess with the sinusoidal waves?

....gosh we are out into the bleachers now 😯

T

If the theory holds together, I'm not sure MV would be all that critical. Are we saying that we don't want a bulge to reach the muzzle at the same time as the bullet? If that's so, and the wave travels through the barrel at the speed of sound and If the bullet and wave start at the moment of full ignition, the barrel wave will reach the muzzle and be on the way back well before the bullet reaches the muzzle. Even in a shorter barrel the the wave can't catch the bullet up second time round as the bullet will be up to the same speed as the barrel wave by the time it has traveled around 14" up the barrel.

[brown dog]

3 minutes ago, 1066 said:

If the theory holds together, I'm not sure MV would be all that critical. Are we saying that we don't want a bulge to reach the muzzle at the same time as the bullet? If that's so, and the wave travels through the barrel at the speed of sound and If the bullet and wave start at the moment of full ignition, the barrel wave will reach the muzzle and be on the way back well before the bullet reaches the muzzle. Even in a shorter barrel the the wave can't catch the bullet up second time round as the bullet will be up to the same speed as the barrel wave by the time it has traveled around 14" up the barrel.

Allan, the wave is travelling at the speed of sound in steel, not in air. I'll look it up, but gets to the muzzle when the bullets barely left the chamber 

[1066]

2 minutes ago, brown dog said:

Allan, the wave is travelling at the speed of sound in steel, not in air. I'll look it up, but gets to the muzzle when the bullets barely left the chamber 

Ok - speed of sound in steel is 5,920 metres per second - around 12x times faster than in air : )  

[1066]

More like 17 times faster  Lucky I'm not trying to land a space craft on an asteroid.

[brown dog]

10 minutes ago, 1066 said:

More like 17 times faster  Lucky I'm not trying to land a space craft on an asteroid.

😂😊

[brown dog]

Just noticed, long has some OBT calculators here: http://www.the-long-family.com/optimal barrel time.htm

We're working back to front with .22lr... is anyone able to give a barrel time value for .22lr match at 1" intervals 14" to 24"?

 

[1066]

Separating the chamber from the barrel would solve all the problems.

[brown dog]

37 minutes ago, 1066 said:

Separating the chamber from the barrel would solve all the problems.

😂

[brown dog]

Right.  I'm bored, so some fag packet maths to try to show what I mean.

QL barrel times for .22lr could make this more meaningful.... but, until someone has the QL approximations, here's my  best approximation (with a valid assumption on .22 acceleration form described in the first photo):

so,

[brown dog]

Remembering those aren't real, but based on the (valid and necessary) assumptions described in the photo, I think my values will be close enough and 'within tolerance'.

Using Long's OBT calculator to identify node times against barrel times:

 

So... taking my valid-assumption-based barrel times as 'close enough', ... we can see the following:

16-19" barrels all have roughly the same low value for muzzle disruption with match ammo ... meaning 17.5" would be a safe 'forgiving of variance' midpoint to pick

20" is nice... but right on the edge of the wheels falling off...so unforgiving of variance and likely to be the most frustrating- sometimes good sometimes seemingly randomly bad

21"-24" have more muzzle disruption and are therefore likely to be consistently less forgiving   ...  (perhaps that's why longer match barrels are choked, to overcome muzzle disruption at this length?)

[brown dog]

If someone has 'real' match ammo velocities and barrel times, it'd be interesting to rerun that; I'd be keen to see if any of the output is sustained by QL approximations 

...that said, it's worth noting that I picked the Tenex published midpoint mv ... so it's probably a good representative value for finding an mv-tolerant sweetspot barrel length

 

[Popsbengo]

19" is optimum in your fag packet calculation.  According to the EXCEL calculator he gives some very different numbers to yours.  I need to understand his calculation method - further reading.

There may be something in this,  but how well does QL actually model barrel time?  There's an assumption in Long's method that QL is strongly correlated to what's really going on.  Bore tolerances must add variance to this?

I have QL but never used it for .22rimfire. I'll have a play.

[brown dog]

24 minutes ago, Popsbengo said:

19" is optimum in your fag packet calculation.  

Why? 16, 17, 18, 19 all show identical delta; so 17.5 midpoint to my eye ? 

If you include the 20 too, (which I don’t because it marks the start of rapid change into the next values) then midpoint 18? 

[brown dog]

7 minutes ago, Popsbengo said:

 According to the EXCEL calculator he gives some very different numbers to yours.  

I used his macro. 

You have to adjust barrel length and then node number (to find values matching your barrel time).

[brown dog]

1 hour ago, Popsbengo said:

 but how well does QL actually model barrel time?  

My calculated barrel times won't be that far out  ... start vel (0) and MV are knowns, as is barrel length. 

A simple approximation would have assumed constant acceleration the whole way,

but I've improved on it with an assumption that acceleration for .22lr takes place from  0" to 16"

and that , from that point,  vel is constant...

which is likely to better approximate reality, certainly close enough for govt work.

...on that methodologically, it'll be in the parish.    

I think 🤔😂 

 

 

To my mind, the only variance QL could introduce would be nuances that challenge my working assumption to treat acceleration as being constant from 0" to 16".... but I'd have thought such nuance would introduce  differences likely to be in  microseconds, rather than milliseconds. 

 

Best gross-error idiot-check would be to confirm my 16" barrel, barrel time: Start 0m/s end 324m/s, distance 16" 😊😊

 

[Popsbengo]

15 hours ago, brown dog said:

My calculated barrel times won't be that far out  ... start vel (0) and MV are knowns, as is barrel length. 

A simple approximation would have assumed constant acceleration the whole way,

but I've improved on it with an assumption that acceleration for .22lr takes place from  0" to 16"

and that , from that point,  vel is constant...

which is likely to better approximate reality, certainly close enough for govt work.

...on that methodologically, it'll be in the parish.    

I think 🤔😂 

To my mind, the only variance QL could introduce would be nuances that challenge my working assumption to treat acceleration as being constant from 0" to 16".... but I'd have thought such nuance would introduce  differences likely to be in  microseconds, rather than milliseconds. 

Best gross-error idiot-check would be to confirm my 16" barrel, barrel time: Start 0m/s end 324m/s, distance 16" 😊😊

 

I've been playing all morning with QL and trying to find .22LR data.  In summary it would seem that 16" is optimum for .22LR velocity and the time taken to travel 16" is approximately 1.5mS.  This appears supported by playing scenarios in QL but there is no .22LR file available so I tried .223 and varied the Mv to match a 40gr .22LR.

Using Long's calculations,  node 15 seems to be in phase with OBT of 1.5mS

 

For interest I pulled a CCI Minimag:

COAL  0.986

Case 0.600

Bullet 0.513 (small hollow base)

Powder 1.5gr of an unknown but I assume very fast powder  (the primer must give quite a contribution)

Case usable volume (H2O)  3.3gr (measured and calculated)

 

[Popsbengo]

I've run some comparisons between my known good load for 6.5CM and the OBT calculations.  The QL calc was tweaked to give the real-world measured Mv for 144 Berger Hybrid doing 2880 fps from 30" barrel

My best load (0.3moa , two off 5 shot groups at 100yds) falls between the OBT calculated nodes - ie in the wrong place!

It also shot like a laser at 600yds.  (Mr Dolphin makes exceedingly nice guns).

Conclusion:  I remain skeptical of the value of this 'theory'.  I shall check further with .338

Recommendation:  find a bullet that your rifle likes, do some load development in the real-world using the "method" of one's choice,  shoot it lots.  Check results, tweak. 😁

[brown dog]

3 hours ago, Popsbengo said:

it would seem that 16" is optimum for .22LR velocity and the time taken to travel 16" is approximately 1.5mS.  

 

That's very quick - and being a mS faster than avg vel calculates (0 to 324 m/s over 16") , would imply that it must be reaching mv speed well in advance of 16".... did it give a bespoke pressure/vel time curve?

[Popsbengo]

3 minutes ago, brown dog said:

That's very quick - and being a mS faster than avg vel calculates (0 to 324 m/s over 16") , would imply that it must be reaching mv speed well in advance of 16".... did it give a bespoke pressure/vel time curve?

No but looking at velocity/time charts on QL in general, the acceleration is much greater initially so your finger in the air 162m/s is too slow I feel.

I picked up the 1.5mS over 16"  from here:  https://sites.google.com/site/thelongrangerimfireclub/home/longrange-rimfire-ballistics

 

[brown dog]

55 minutes ago, Popsbengo said:

No but looking at velocity/time charts on QL in general, the acceleration is much greater initially so your finger in the air 162m/s is too slow I feel.

I picked up the 1.5mS over 16"  from here:  https://sites.google.com/site/thelongrangerimfireclub/home/longrange-rimfire-ballistics

 

That sounds far too quick; this is a 6br going  three times faster at shot exit

[brown dog]

Thinking on.... even if a 22lr instantaneously accelerated from 0m/s to 324m/s in the first 0.0001mm of barrel;

and did all 16 inches at 324m/s...which, clearly it doesn't..

.... it'd take 1.28mS  to do 16"

...so 1.5mS fails a commonsense check to my mind.

 

(PS edit:   

Note in the 6br graph how S-shaped the acceleration curve is - interpolating to a broadly linear acceleration... this is because the X axis on the graph is 'time'.     

Similar QL graphs, appearing to show faster initial acceleration have the X axis as distance (rather than time) which shows 'where' the acceleration happens, not 'when' it happens - which gives a subtly, but significantly different visual:

 

)

 

[Popsbengo]

1 hour ago, brown dog said:

Thinking on.... even if a 22lr instantaneously accelerated from 0m/s to 324m/s in the first 0.0001mm of barrel;

and did all 16 inches at 324m/s...which, clearly it doesn't..

.... it'd take 1.28mS  to do 16"

...so 1.5mS fails a commonsense check to my mind.

 

(PS edit:   

Note in the 6br graph how S-shaped the acceleration curve is - interpolating to a broadly linear acceleration... this is because the X axis on the graph is 'time'.     

Apparently similar graphs, appearing to show faster initial acceleration have the X axis as distance (rather than time) which shows 'where' the acceleration happens, not 'when' it happens - which is subtly, but significantly different)

 

looking at these graphs from Geoffrey Kolbe's P-Max program, I've used finger in the air to get similar to .22LR ballistics:

75% of the acceleration is all in the first 4 inches.  The pressure curve shows pressure to 1.75mS, so I've taken that as barrel time.

Am I missing something here?  I read this to show a Mv of 1061 fps achieved in 1.75mS in a 16" barrel

[brown dog]

3 minutes ago, Popsbengo said:

looking at these graphs from Geoffrey Kolbe's P-Max program, I've used finger in the air to get similar to .22LR ballistics:

75% of the acceleration is all in the first 4 inches.  The pressure curve shows pressure to 1.75mS, so I've taken that as barrel time.

Am I missing something here?  I read this to show a Mv of 1061 fps achieved in 1.75mS in a 16" barrel

?

Plot one showing velocity against time, not distance.

I've got a pretty strong audit trail to my calculation; you seem to be plucking numbers🤔😊

[Popsbengo]

1 minute ago, brown dog said:

?

Plot one showing velocity against time, not distance.

I've got a pretty strong audit trail to my calculation; you seem to be plucking numbers🤔😊

Not at all,  as I said, there's no .22LR data I can find so I've just made a imaginary cartridge that has fast powder, achieves something similar to .22LR in a 16" barrel at the muzzle.  I can't plot anything else as Kolbe's program just gave me that output.