Bill & Al discussion.....

[IndianaJames]

I would like to thank Bill and Al for discussing this in front of all of us. I hope this thread can be used for comments and keep the discussion thread uncluttered.

I would like to know if Al's animations are considering the initial movement of the barrel...the one that counts. Is it modeled on the first rise of the muzzle from rest when the bullet is still in the barrel? Does the bullet leave the muzzle on the first cycle, or does it take the ride for X number of cycles before it exits?

Thanks again, guys!

Jim

 

[pacecil]

The curves that show muzzle movement show right where the bullet exits, as well as before and a little bit after. These curves, and there are many of them, indicate lower velocity bullets may exit after one or two cycles, while faster bullets will exit during the first cycle.
Muzzle movement before the bullet leaves probably shouldn't be called a "cycle". This is a period during which the pressure against the bolt face causing movement is still being applied and the movement may not strictly be in the form of a regular repeating cycle. It's the natural vibration that occurs after gas pressure has dropped to zero that is a regular repeating "cycle".
The pictures that show barrel vibration show the entire recoil time, that is while the bullet is in the barrel and afterward.

 

[IndianaJames]

Muzzle movement before the bullet leaves probably shouldn't be called a "cycle".

That's what I was getting at. Do we really care about the vibration after the bullet exits unless we can use it to predict what the "bullet in the barrel" movement is? Is the "BITB" wave congruent with the natural barrel vibration?

It's beyond me, and it seems like it would be a bear to model that first movement. I'm really looking forward to this discussion.

Jim

 

[Madrox]

The curves that show muzzle movement show right where the bullet exits, as well as before and a little bit after. These curves, and there are many of them, indicate lower velocity bullets may exit after one or two cycles, while faster bullets will exit during the first cycle.
Muzzle movement before the bullet leaves probably shouldn't be called a "cycle". This is a period during which the pressure against the bolt face causing movement is still being applied and the movement may not strictly be in the form of a regular repeating cycle. It's the natural vibration that occurs after gas pressure has dropped to zero that is a regular repeating "cycle".
The pictures that show barrel vibration show the entire recoil time, that is while the bullet is in the barrel and afterward.

Pacecil,

This is not an SA question, it is seriouus. Why do we care what vibrations occur AFTER the bullet has left the barrel. I mean assume it takes 10 minutes for the bullet to strike the target after leaving the barrel. I could put the gun up and leave in that amount of time and the bullet would not be affected. So, do we care?

 

[Vibe]

Pacecil,

This is not an SA question, it is seriouus. Why do we care what vibrations occur AFTER the bullet has left the barrel. I mean assume it takes 10 minutes for the bullet to strike the target after leaving the barrel. I could put the gun up and leave in that amount of time and the bullet would not be affected. So, do we care?

And it's a good valid question. Truth is, No, we don't care what goes on after the bullet has left. However - the natural vibration pattern takes shape in the formation of that first cycle. This in itself is a useful tool in determing where the barrels muzzle will be pointing at the instant that the bullet escapes, and thus the direction that the bullet will be traveling at that instant. If the bullet leaves at a null point AND during a period of the "end of travel" then the vertical rate of change of the muzzle is at a minimum - which leads to a more consistent state of exit from shot to shot. Consistency leads to accuracy.

 

[pacecil]

Indiana James.....That's what I was getting at. Do we really care about the vibration after the bullet exits unless we can use it to predict what the "bullet in the barrel" movement is? Is the "BITB" wave congruent with the natural barrel vibration?
It's beyond me, and it seems like it would be a bear to model that first movement. I'm really looking forward to this discussion.
Exactly, we don't care about "before" or "after" - it's only that instance in time right when the bullet departs the muzzle. We have to study the "before" to determine what happens at the muzzle.

 

[pacecil]

madrox....This is not an SA question, it is seriouus. Why do we care what vibrations occur AFTER the bullet has left the barrel. I mean assume it takes 10 minutes for the bullet to strike the target after leaving the barrel. I could put the gun up and leave in that amount of time and the bullet would not be affected. So, do we care?
See my post to Indiana James above and Vibes post above that.

 

[IndianaJames]

Sort of...

OK. I did the math; and, this is not the "new" math. It's been a long time since high school, but I still remember D=RT.

Varmint Al lists the Mode 2 frequency as 406Hz. This is on a 22 inch barrel. Since we use about 26 inch barrels, I think that would make it about 345Hz. Now add a tuner to effectively add 5 inches to the resonating length and get about 300Hz. This would give us a 7.4ms period(I think that's the term for the time of one cycle).

Now, a whole bunch of assumptions later, I used 550ft/sec for the average speed of the bullet...roughly half the muzzle velocity. This answers my own question above, as using these calculations(4.3ms BITB) the bullet exits after about one and three/quarter full cycles...260º of the second cycle.

I still don't have a clue where to start the clock to synchronize the bullet to the vibration, and I have this non-educated feeling the first "resonant cycle" of the barrel is not as short as the following ones. That pressure in the tube surely doesn't cause it to start vibrating as it would if you just "twanged" it.....does it?

Please feel free to add to my confusion.

Jim Pherson

PS: OK. I did that backwards! It comes out 210º on the first cycle...wrong number on top! Still ugly, but hopefully someone knows the actual BTIB for Eley Match and it will get better.

 

[mks]

That's good math

That pressure in the tube surely doesn't cause it to start vibrating as it would if you just "twanged" it.....does it?

Jim,
Your math skills are not failing you. The steady state vibrations are not nearly as important as the transient response. The force on the bolt face is above the center of gravity of the rifle, and causes angular acceleration of the action. This angular motion propagates forward along the barrel.

Cheers,
Keith

 

[pacecil]

Hey Beau!....

I just read this on your post for Calfee....As I have time we'll get into the difference between having the muzzle STOPPED, or just having it stationary, and what causes it. ( a hint.....the node, or dead spot, does not form an X shape, as Al's computer graphics suggest)
Now, I'm not being asinine or condescending (but I'm probably being a smart a**) but....wait a minute!...wipe that smile from your face! This is no laughing matter!

 

[B. Harvey]

One cycle at 406hz would have a barrel time of .00246 seconds.

IF, and this is a big IF, the nodes in the system, from action to the node, equate to the half wave, then a true frequency can be found. If the 22" barrel's node was 4.4" behind the muzzle, the half wave would then be 17.6" and a full wave is 35.2", which would put the frequency at 383.63 hz.

Now, say barrel time is .00246 seconds, you would then have 1.06 cycles by bullet exit.

IF, the nodes correspond to the actual frequency, then moving the node forward, closer to the muzzle, would put the system even farther from the one cycle tuning.

 

[Beau]

I just read this on your post for Calfee....As I have time we'll get into the difference between having the muzzle STOPPED, or just having it stationary, and what causes it. ( a hint.....the node, or dead spot, does not form an X shape, as Al's computer graphics suggest)
Now, I'm not being asinine or condescending (but I'm probably being a smart a**) but....wait a minute!...wipe that smile from your face! This is no laughing matter!

It's the smartass part that just lowers you a notch. You can be critical, you can even point out your way of seeing things. You can be a smartass if you want, but no good deed goes unpunished.

You know, I could be wrong, but I don't think I've ever really read anything significant from you. It's usually vaguely condescending. Must feel good to be the smartest man in the world. Well you may not be the smartest but top 5% anyway. You and the other 299,999,999 (approx)

 

[Lynn]

Hey Vibe and Pacecil

Now, a whole bunch of assumptions later, I used 550ft/sec for the average speed of the bullet...roughly half the muzzle velocity. This answers my own question above, as using these calculations(4.3ms BITB) the bullet exits after about one and three/quarter full cycles...260º of the second cycle.Isn't 260 degrees pretty close to my 270 degree anti-node were the barrel would be moving its slowest and have the most "Area under the curve"?

Didn't Pacecil say earlier that waves in steel don't reflect back like other waves do? Why would we get a transient wave in steel if it doesn't react the same?
Waterboy

 

[D R Greysun]

My question for Al........!

How much angular difference at the muzzle over a duration of 0.014 ms? That's assuming barrel has been tuned so that off-node/anti-node is at 0.5 inches short of the muzzle? Or 'what if' the barrel is tuned so the off-node/anti-node is moved to the muzzle? Also, could off-node/anti-node as indicated be considered parallel for each barrel? Note: I node not the proper term for that proportion of the two line coming together at the point in the graph. To a common person such as myself, the vibrations appear nearly 'stopped' for a period of time.

D R

PS: Al please allow me the use of your graph for this illustration. dr

 

[tim]

It's the smartass part that just lowers you a notch. You can be critical, you can even point out your way of seeing things. You can be a smartass if you want, but no good deed goes unpunished.

You know, I could be wrong, but I don't think I've ever really read anything significant from you. It's usually vaguely condescending. Must feel good to be the smartest man in the world. Well you may not be the smartest but top 5% anyway. You and the other 299,999,999 (approx)

Remember, you encouraged him a while back. No good deed goes unpunished

 

[Beau]

I encouraged him when he was in rehab or something. Not bad when he's on the meds or off them as the case may be.

 

[Carp]

It's the HALF WAVE THEORY of the stopped muzzle. The stopped muzzle is the bullet leaving the muzzle at the HIGHEST point of muzzle travel at the EXACT SAME TIME. The other half of the wave is not useable ( with the exception of a theory that says the gun doesn't have to wait on you). It's simple folks. You don't need great math skills. You want the highest point of the HALF wave to be the exit point of the bullet. You cannot make any math do it for you to determine the tuner setting. IT STILL takes testing. More discussion only leads to more confusion and only to ultimately more fighting. If the theory holds water then the CF shooters really ought to know because they can control their ammo more than we do. Otherwise it is all still just theory. A great shooter, with great ammo can overcome this for some time (I don't know how long). Their scores can be awesome in the RF world. That is why a great shooter will always be a bigger threat than a great gun. Can that be any simpler?

Carp

 

[pacecil]

Hey Beau!

Did you see what Al said?......You are making statements without anything to back them up except faith. You need to show some evidence of what you are saying.
Yeh, that's what you would expect from one of them condescending, smarter than everybody, engineers! You and Tim better straighten him out! He's probably one of them keyboard shooters as tim calls 'em! Oh, and by the way, a few posts back you were going on how you beat me in that BR match. Hell, I'm a blind old man, shooting a 60 year old home made 52, using cheap SK ammo....a five year old could have beat me!

 

[Varmint Al]

I {know} not the proper term for that proportion of the two line coming together at the point in the graph.

D R
PS: Al please allow me the use of your graph for this illustration. dr

D R,
The two curves coming together is a mere coincidence. There is no meaning there. The Muzzle Projection Curves are where the muzzle is pointing in time as the bullet travels up the bore. It would be like having a laser taped to the barrel and watching it move on the 50 yard target. I wrote a small BASIC program to take the last 1/2 inch of the muzzle and extend a straight line from the muzzle to the 50 yard target.

No problem with altering the picture file. I am only trying to explain what is going on when a rifle is fired.
Good Hunting... from Varmint Al

 

[D R Greysun]

D R,
The two curves coming together is a mere coincidence. There is no meaning there. The Muzzle Projection Curves are where the muzzle is pointing in time as the bullet travels up the bore. It would be like having a laser taped to the barrel and watching it move on the 50 yard target. I wrote a small BASIC program to take the last 1/2 inch of the muzzle and extend a straight line from the muzzle to the 50 yard target.

No problem with altering the picture file. I am only trying to explain what is going on when a rifle is fired.
Good Hunting... from Varmint Al

Thank you for the reply Al, OK, I see what your graph represents. I have been trying to make the point that where the last 0.5 to 1.0 inch of the barrel is pointed at the time the bullet exits is the critical part. All the other gyrations are meaningless. If I can believe Quickload, the difference between a 1036 fps bullet and a 1085 fps bullet transversing the last inch of a 23 inch barrel is 0.014 ms. Seems if the barrel can be tuned (dampened) to co-inside with that small area of 'whatever you call it' at the muzzle for close to 0.014 ms (1.4e-005 seconds?) for all practical purpose the barrel would be stopped. Is this not within the realm of possibility? TIA

D R