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jGEE
06-07-2009, 12:14 AM
"POW" vs "PUSH"
B.S. theory, :POSTULAS:
Two identical rimfire bullets 40g, same weight/density ect. Only difference is powder charge/charastic. One powder is slow burning "push", the other powder is fast burning "pow". Both bullets leave the bbl at the same speed, say 1050 fps.

The "push" burns slower and takes the full length of the bbl to acclerate the 40g pill to 1050 fps. The "pow" burns faster and acclerates the 40g pill to 1050 fps in half the distance.

Can the 40g pill/bullet have 2 different amounts of "stored energy" from different acceleration charastics?... i'm sure the answer is no but i say yes.
I know this is probably "out there" but which accleration rate will make the bullet fly farther and flatter???

Probably everyone would agree the burn rate would effect the way the bbl vibrates. Both bullets leave the bbl at 1050 but bbl viberations would be different. Burn rate may also effect the "harmonic hum" of the bullet in flight also.
Any thoughts, Mr pacecil, your thoughts other than i'm crazy, lol.

Just a thread for discussion, you never know where they will go. joe :)

Joe Haller
06-07-2009, 03:08 AM
I would say that the faster burning powder that allows the bullet to coast the second half of it's passage down the barrel, will have less gas pressure on exit at the muzzle.

If the base of the bullet is ever so slightly deformed, or the muzzle does not have an even, well lapped crown: The more violently escaping gasses from the slow burning powder, would tend to tip the bullet more than the bullet that has been coasting the last half of the barrel length. That tipping will result in yaw or the "corkscrew" effect and will degrade accuracy. The faster a bullet "goes to sleep" after it leaves the muzzle, the less it will be affected by wind drift.

One of the reasons match grade rimfire rifles have longer barrels? The other one would be to keep those bullets below the speed of sound.

It also seems to me that if a bullet with less pressure behind it at bullet exit results in less yaw, then the bullet will have a shorter time of flight, resulting in flatter trajectory and longer range.

JOE Haller

Roger T
06-07-2009, 08:29 AM
Both bullets leaving the barrel at the same Vel. would have the same stored energy/ballistic track. Accuracy was not mentioned in the question but as stated above may be different for each burn rate. My .02 anyway. Chronys are typically set up at about 10-15 ft. after the muzzel the readings are then corrected for muzzel vel.So it would be hard to account for added Push or lack thereof between the powder burn rates as long as the Chrony speeds were the same.

David Valdina
06-07-2009, 08:40 AM
When playing football, when you are accelerating when you hit another player coming at you, it hurts less, than when you are slowing up and the collision happens, even if the combined collision speeds are identical. This experience might lead some to think some differences might exist with bullets leaving the barrel.

Beau
06-07-2009, 09:15 AM
[QUOTE=jGEE;510042]"POW" vs "PUSH"
B.S. theory, :POSTULAS:

The "push" burns slower and takes the full length of the bbl to acclerate the 40g pill to 1050 fps. The "pow" burns faster and acclerates the 40g pill to 1050 fps in half the distance.

/QUOTE]

I guess there is no friction or other resistance in the second half of that barrel so the bullet having been accelerated to to its full velocity in half the barrel length does not begin to slow.

jGEE
06-07-2009, 09:37 AM
[QUOTE=jGEE;510042]"POW" vs "PUSH"
B.S. theory, :POSTULAS:

The "push" burns slower and takes the full length of the bbl to acclerate the 40g pill to 1050 fps. The "pow" burns faster and acclerates the 40g pill to 1050 fps in half the distance.

/QUOTE]

I guess there is no friction or other resistance in the second half of that barrel so the bullet having been accelerated to to its full velocity in half the barrel length does not begin to slow.

"Both bullets leave the bbl at the same speed, say 1050 fps." I wasn't concerned with the bullet fps anywhere in the bbl just the exit speed as i stated. I thought it would be obvious that for the "pow" to quit pushing at half track the pill would have to be faster than 1050 to exit at 1050. You gotta work with me here, lol.

... and yes i was thinking which would be more "ACCURATE".

Mr haller has an interesting thought:
I would say that the faster burning powder that allows the bullet to coast the second half of it's passage down the barrel, will have less gas pressure on exit at the muzzle.

It makes me think of the pappas noodle -maybe the noodle lets off gas pressure slowly?.. Now this is a very interesting thought to me i wasn't thinking about. It will take some mulling around in my brain. I can only "mull" on one thing at a time -i'll put it in 'quea, lol!

J Pappas
06-07-2009, 12:36 PM
[QUOTE=Beau;510079]

"Both bullets leave the bbl at the same speed, say 1050 fps." I wasn't concerned with the bullet fps anywhere in the bbl just the exit speed as i stated. I thought it would be obvious that for the "pow" to quit pushing at half track the pill would have to be faster than 1050 to exit at 1050. You gotta work with me here, lol.

... and yes i was thinking which would be more "ACCURATE".

Mr haller has an interesting thought:

It makes me think of the pappas noodle -maybe the noodle lets off gas pressure slowly?.. Now this is a very interesting thought to me i wasn't thinking about. It will take some mulling around in my brain. I can only "mull" on one thing at a time -i'll put it in 'quea, lol!

The noodle works because of the air being compressed in front of thje bullet. It exits the holes in the noodle at the first place it can, the holes in the noodle.

pacecil
06-08-2009, 12:02 AM
I can’t tell you, which is better, a “push”or a “pow”. What I can do is give you some things to think about and maybe you can solve the problem yourself.

First, there is essentially no difference in “stored energy” in bullets that leave the muzzle at the same velocity. Energy of the moving bullets depends on velocity and weight. It makes no difference how they were accelerated up to their velocity.

Second, you have to look at the pressure-time curves. A fast burn pow load is going to reach a high peak very quickly and then fall off rapidly. A slow burn push load is going to have to come to a lower peak at a later time and then fall off at a rate that keeps the average prassure force on the bullet bases the same. This is important: the curves have to be such that the average pressure will produce the same velocity. I can’t say wich load would have the highest exit pressure but probably they would be pretty close.

Third, unless you had a pow load that in effect produced an EXPLOSION or IMPACT on the bullet I doubt you would see much difference in effect from the two loads. Based on pressure-time curves I’ve seen, you just can’t get this kind of effect with normal powders. However if you did introduce deformation or vibration in the bullet then in theory you could see an effect on accuracy… It’s like throwing a ball 100 yards with your arm and hitting a ball 100 yards with a bat – you know the batted ball is deformed and vibrating and this would affect it’s flight. But remember, that was IMPACT with the bat!

I’m sure someone is going to grab on to that “higher peak pressure” with the pow load and say this could cause deformation and change the bullets flight but again it’s a matter of degree. Repeating myself: I don’t think the difference in loads THAT MUST PRODUCE THE SAME AVERAGE VELOCITY will result in a significant difference in deformation.

David Valdina
06-08-2009, 07:39 AM
and perhaps a grant to fund the study. Take a carbine length rifle, and play with loads using cast bullets until you find identical velocities as close to the muzzle as you can measure. One load using Bullseye powder, which I think is suppose to burn completely in a 2" barrel and the other load using the slowest rifle powder you can find, one where when you shoot it, you see the flame extending out many feet so you know it is still generating expansion when the bullet is launched, and then test your results.

Now, if I only could find primers to buy...

But I will speculate that the quick burn (fully burned powder) potentially will produce more consistency than the still burning. In quick burn you know 100% of the powder has been used up and the friction of the barrel is now slowing the bullet in the barrel. In the slow burn, you may not be able to predict what percentage of the powder has been burned by exit, maybe more true with less than 100% loading densities. Also, in a lead bullet, perhaps the flame melts a wee bit of the bullet. It may be better to have had the flame die out and the lead not as soft at exit, as opposed to the flame burning the tail end of the lead as it exits. My speculations.

jGEE
06-08-2009, 10:26 AM
Also, in a lead bullet, perhaps the flame melts a wee bit of the bullet. It may be better to have had the flame die out and the lead not as soft at exit, as opposed to the flame burning the tail end of the lead as it exits. My speculations.

mr valdina That would be an interesting experiment and that's another interesting thought! I didn't even consider the temp of the bullet in pow vs push but i bet there would be a difference in lead temp.

We're talking about very small differences but maybe when your trying for 1 hole groups maybe it does matter. I think something is going on when you use different rimfire ammo besides just the speed.

mr pacecil what about does the temp of the bullet influence it's ability to "store energy"?
I wonder if it's the temp of the bullet that influences flight along with speed?? i think something is something is going on besides exit speed! Now i'm just fishing but maybe the temp differential of the bullet and air temp maybe does something.

I know as little of a 10 degree increase in outside temp can change the way a rimfire bullet flies. I was thinking it was the speed of the bullet thru the air made the difference, maybe bullet/air differential is at work also? joe :)

pacecil
06-08-2009, 01:05 PM
A bullet accelerates for the full length of barrel regardless of whether fast burn or slow burn powder is used. It will accelerate at a slower rate as it nears the muzzle but it is still gaining velocity. It never "coasts". It is only in rim fire that pressure might drop so low and friction forces be so high that conditions be set up to allow a bullet to slow down. This would be very unusual and probably never happens. It certainly never happens in center fire.

Pressure behind the bullet does not drop to zero when burning stops. This applies with fast or slow burning powders. Pressure stops building up when burning stops and then falls as the volume of space behind the bullet increases, and as the gas temperature drops. It only drops to zero when the bullet leaves the muzzle.

There is not enough time for the burning temperature to have much effect on the bullet. It's like waving your hand through a flame. The surface may reach melting point briefly and the whole bullet may rise in temperature slightly. The effect of friction and hot gas on base means the bullet will leave the barrel warmed up but probably not enough to effect flight.

This slight warming of the bullet does mean it has some "stored energy" in the form of heat. The moving bullet also has "stored energy" in the form of kinetic energy due to its velocity and weight. It's doubtful heat energy in the bullet has any effect on accuracy but the kinetic energy probably does.

This is off subject but I have a question about the "noodle". Does the air escape through the holes faster than it would into free space?

blades
06-08-2009, 01:43 PM
In regards to pressure escaping behind bullet,possibly deflecting flight line, take a look at the latest top Olympic air pistols. All are drilled to relieve pressure prior to the pellet exiting the barrel in addition to the compensator (or stripper) at the muzzle. The reasoning, I was told, was to eliminate the possibility of high pressure air deflecting the pellets path at the critical instance of pellet exiting barrel. I also seem to remember various discussions in this vein many years back regarding the sight radius extension tubes (bloop tubes in rimfire) which were not ported affecting accuracy due to containment of exiting gases rushing past the bullet. Reported cause was deposits on muzzle building up into the crown area which we are aware of with the tuners.

Beau
06-08-2009, 02:02 PM
A bullet accelerates for the full length of barrel regardless of whether fast burn or slow burn powder is used. It will accelerate at a slower rate as it nears the muzzle but it is still gaining velocity. It never "coasts". It is only in rim fire that pressure might drop so low and friction forces be so high that conditions be set up to allow a bullet to slow down. This would be very unusual and probably never happens. It certainly never happens in center fire.

It can't accelerate and slow down both. That's impossible. However, common sense would tell you that the bullet eventually starts to slow. Think of it in extreme terms. If you had a barrel a mile long, how fast would a 22-250 exit the muzzle. I don't think it would exit at all, which tells me that it slows down somewhere.

In relation to rimfire, it is well documented that the velocity is generally max at 16" and slows at a rate of about 10 FPS in a 24" barrel. Call that coasting or friction or whatever, it still slows.

pacecil
06-08-2009, 05:39 PM
See the problems caused when we don't put numbers on these things! If I had said the bullet had an acceleration of -100fps, there would have been no confusion! You would have seen that -100 number and all would have been clear!

You have to have a clear understanding of what causes velocity of a moving object to change. Basically the bullet will accelerate when the pressure against the base is greater than the friction drag from bore contact. When pressure force drops lower than the friction force the bullet will accelerate in the opposite direction. This is negative acceleration (deceleration). Or you can call it "slowing down". Now, remember what I said: It is only in rim fire that pressure might drop so low and friction forces be so high that conditions be set up to allow a bullet to slow down

Where this might happen in a barrel, that is where the bullet might start slowing down, depends only on the value of those two forces. Could be, it happens around 16" in most rim fires. If you look at a pressure-time curve for a typical 22 rim fire (look in Varmint Al's site for good one of these) it does drop to about 600 psi at about 16" down the barrel and this is roughly where it could drop below the friction force - so, it all makes sense doesn't it?

DonMatzeder
06-08-2009, 06:23 PM
Cecil, this all depends on whether the barrel is straight. With just a little curve, we can keep the pill accelerating the length of the barrel no matter how long.

Beau
06-08-2009, 07:54 PM
See the problems caused when we don't put numbers on these things! If I had said the bullet had an acceleration of -100fps, there would have been no confusion! You would have seen that -100 number and all would have been clear!

You have to have a clear understanding of what causes velocity of a moving object to change. Basically the bullet will accelerate when the pressure against the base is greater than the friction drag from bore contact. When pressure force drops lower than the friction force the bullet will accelerate in the opposite direction. This is negative acceleration (deceleration). Or you can call it "slowing down". Now, remember what I said: It is only in rim fire that pressure might drop so low and friction forces be so high that conditions be set up to allow a bullet to slow down

Where this might happen in a barrel, that is where the bullet might start slowing down, depends only on the value of those two forces. Could be, it happens around 16" in most rim fires. If you look at a pressure-time curve for a typical 22 rim fire (look in Varmint Al's site for good one of these) it does drop to about 600 psi at about 16" down the barrel and this is roughly where it could drop below the friction force - so, it all makes sense doesn't it?

That's engineering speak. Since my brother is an engineer, I've been exposed to it for quite sometime and have learned to speak a little. I remember when I was about 13 I used to take my bicycle to the top of a hill where there was road construction going on. It was a steep hill and I wanted to see how far I could coast. I would accelerate for quite sometime and then begin negative acceleration until the point that both acceleration and velocity reached zero and the bicycle would topple over (took me a while to learn to use my feet). I remember the last time I tried that, I hit a "quick negative acceleration" rock. I think the bicycle actually began negative velocity and acceleration, but I continued forward for what seemed like a long time until I hit the negative acceleration ground. Negative acceleration can be rough on you. I can't really put any numbers on that so it may not be too clear.

Anyway, I'm an accountant. We're the guys who couldn't make it as engineers. And tonight I read your last post just before a late meeting with a client and I thought of a very practical use for your explanation. This guy seems to think that the bad economy has caused him to lose several million dollars, but I explained that he was still really making money and lots of it. It's just negative money and I put a number on it for him and a projected number of the final negative money he would make before he would hit rock bottom and final negative acceleration. You were right, putting a number on it makes people happy. I never saw a guy so happy. He started laughing right there at the conference table and laughed all the way out the door. Good client but he said something about he may not come back for a while. So I guess I solved his problem.

J Pappas
06-09-2009, 05:05 PM
Pacecil, did you get my PM?

pacecil
06-10-2009, 08:29 AM
O, I missed that - I'll answer you shortly.