air going over the nose of the sub sonic bullet is super sonic MAY be, not always. Remember, we're pushing air out of the way and venturi effect MAY increase the velocity. Just like lift of a wing, air has to speed up to get around the curved surface or low presure area is developed. Oh, that's a BT bullet! The velocity vector (forward and down, i.e. yaw angle) mean the velocity around the body is faster than at the nose (for ogival bullet). So pressure on the bottom of the body is greater than the top. Same for nose but as the body has greater surface area, force to generate yaw is greater. No matter what the forward velocity! Super sonic makes it worse due to pressure 'ridges' or 'shock waves'. THe pressure ridges 'move' relative tothe bullet as fps changes in the transonic region. Spin momentum keeps it stabilized to a point but sudden yaw will cause the gyro to presesand go off axis quite rapidly. The real and only sucessful solution is to keep it supersonic all the way. Really hard to do. That is why we have the 50BMG for 'reaching out and touching someone'! Only other solution is big, heavy and slow. We get to try stuff that is not optimal. Known as LOL.
Effects of Transition Speed
- Thread starter Snakeoil
- Start date
fiver
Well-Known Member
i see snakeoil asked about COG and if it is important.
where that COG is, is important.
as the air moves over and changes course the highest effect of the buffeting on the bullet of course moves.
if the cog is forward and the air is right there moving things around the COG is more affected.
think about someone doing a flip in the air their COR and COG is actually moved away from the body.
do that to a bullet and it too is making that same motion.
keep the COG back away from those affects and the bullet is able to fight the nose moving around and continue in a forward stable[ish] position.
where that COG is, is important.
as the air moves over and changes course the highest effect of the buffeting on the bullet of course moves.
if the cog is forward and the air is right there moving things around the COG is more affected.
think about someone doing a flip in the air their COR and COG is actually moved away from the body.
do that to a bullet and it too is making that same motion.
keep the COG back away from those affects and the bullet is able to fight the nose moving around and continue in a forward stable[ish] position.
Ian
Notorious member
Sort of, but mainly the nose, regardless of shape, starts to compress a pressure wave in front of it as it approaches mach 1. That pressure wave in effect increases the frontal surface area of the bullet many times over and becomes very audible. Eventually the nose pierces the pressure wave and we get sonic boom. What Popper and Fiver are talking about is when the bullet is half in, half out of that pressure wave is when stability goes to hell because the front of the bullet and the back are acting in completely separate mediums with different stability rules and requirements.
RBHarter
West Central AR
Gyro stability , aero stability , COG and CoP ........ I'm dizzy already .
Mechanics over simplified version .
You have to match speed and twist to the nose shape and weight distribution .
To a degree nose shape and weight distribution within the bullet may make a bullet that on paper shouldn't stabilize or is on the outside edge of stability rock solid . Twist can make it or break it , see monolithic copper . Then we have the behind center target/varmint HP that should be resistant to tip but when we get them in that 8.5" 7mm barrel and drive them with a 280AI or RM knocking on 3kfps or more and a little nose defect becomes a big deal .
Of course then we have me pouring/alloying for useable expansion vs the target guy that can shoot a HT lino with good results while upsetting the thumb rules and all of us that are well beyond "you'll have terrible leading at anything past pistol speeds" shooting .
Mechanics over simplified version .
You have to match speed and twist to the nose shape and weight distribution .
To a degree nose shape and weight distribution within the bullet may make a bullet that on paper shouldn't stabilize or is on the outside edge of stability rock solid . Twist can make it or break it , see monolithic copper . Then we have the behind center target/varmint HP that should be resistant to tip but when we get them in that 8.5" 7mm barrel and drive them with a 280AI or RM knocking on 3kfps or more and a little nose defect becomes a big deal .
Of course then we have me pouring/alloying for useable expansion vs the target guy that can shoot a HT lino with good results while upsetting the thumb rules and all of us that are well beyond "you'll have terrible leading at anything past pistol speeds" shooting .
CZ93X62
Official forum enigma
I am not very scientifically-minded. I strive to be that way, but I fall short. I DO pay attention to what myself and others do, to see via observation and reportage "What Works" and "What Doesn't Work". On occasion, calculated & predicted outcomes surprise us.
An example from my own experience. I once had a very nice Savage 99 in 250 Savage, made in 1930. Its rifling twist was the 1-14" pitch, bemoaned by many as incapable of stabilizing bullets over 87 grains in weight (length). Bull Twinkie--it did a fine job with 100 grain spitzers of several makes at 2600-2700 FPS, and did SUPERB work with an NEI 107 grain bore rider at 1400-1700 FPS that looked like an RG-4 or my SAECO #301 that got shrunk in the wash.
At some point--you need to shoot your chosen bullets in your firearms. I value the insights of others derived from their experiences, and often make "Yay or nay" decisions to purchase based on those informed viewpoints. But ultimately--ya gotta get out from behind the keyboard and pick that rifle or revolver up AND BUST SOME CAPS.
Which reminds me......I have 44 and 45 caliber pistol brass in the tumbler, which should be ready for media separation.
An example from my own experience. I once had a very nice Savage 99 in 250 Savage, made in 1930. Its rifling twist was the 1-14" pitch, bemoaned by many as incapable of stabilizing bullets over 87 grains in weight (length). Bull Twinkie--it did a fine job with 100 grain spitzers of several makes at 2600-2700 FPS, and did SUPERB work with an NEI 107 grain bore rider at 1400-1700 FPS that looked like an RG-4 or my SAECO #301 that got shrunk in the wash.
At some point--you need to shoot your chosen bullets in your firearms. I value the insights of others derived from their experiences, and often make "Yay or nay" decisions to purchase based on those informed viewpoints. But ultimately--ya gotta get out from behind the keyboard and pick that rifle or revolver up AND BUST SOME CAPS.
Which reminds me......I have 44 and 45 caliber pistol brass in the tumbler, which should be ready for media separation.
"'Overstabilization' is a myth." -- I'll take you on. It is not only a myth but impossible! Stability is binary. A stationary rock is stable, a moving one is not - it cannot be over-stationary. The equation we use is just a ratio of linear momentum vs angular momentum. The mass terms cancel so we speak velocity. It is stable if the vectors(axis) of radial and linear momentum coincide. Overspun is a reality - but by it's self is of no effect. Energy is used to convert rotational momentum to linear momentum (precession) and cause both axis to diverge (momentarily). Gravity is a good source of the disturbance. Air is also.
See, I didn't step into 'it'.
See, I didn't step into 'it'.
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Ian
Notorious member
Dang Popper, there you go and ruin all the drama with facts.
This is it in a nutshell, applied to cast bullet ballistics. If you think you have some sort of speed limit or rpm threshold theory or whatever you want to call it, what you in fact have is the results of allowing angular mass to become a variable. That usually happens during the first 1/4" of bullet travel. No variable, no effect.
This is it in a nutshell, applied to cast bullet ballistics. If you think you have some sort of speed limit or rpm threshold theory or whatever you want to call it, what you in fact have is the results of allowing angular mass to become a variable. That usually happens during the first 1/4" of bullet travel. No variable, no effect.
Snakeoil
Well-Known Member
I've never heard the term "overstabilization". I would tend to respond similar to what Popper said, but using stable rather than stationary as the variable and again, either yes or no, hence binary in his terms. I'm defining stable in this case in the context of a bullet spinning on it's axis uniformly.
Where I could see it having meaning would be in something being stable longer. An example would be one of those spinning tops that spin on their mushroom end until they reach a certain speed and then begin to wobble as it slows and the shaft rotates about the center until it flips over and spins on the shaft. If you spin it faster it will remain stable on the mushroom end longer. In terms of a bullet, if you are shooting to 100 yds, the bullet only had to be stable out to that range. But if the bullet is stable out to 500 yds, then the twist rate is over-stabilizing the bullet for the intended purpose. But it's really a definition thing that defines how long something is stable while in-flight.
In the case of a long skinny bullet, is it possible that the bullet goes thru a critical speed where it bends only to become straight again once passing thru that critical speed? Granted, a bullet is an extremely short and fat shaft. But gotta wonder if there is a critical speed for a long skinny bullet.
Where I could see it having meaning would be in something being stable longer. An example would be one of those spinning tops that spin on their mushroom end until they reach a certain speed and then begin to wobble as it slows and the shaft rotates about the center until it flips over and spins on the shaft. If you spin it faster it will remain stable on the mushroom end longer. In terms of a bullet, if you are shooting to 100 yds, the bullet only had to be stable out to that range. But if the bullet is stable out to 500 yds, then the twist rate is over-stabilizing the bullet for the intended purpose. But it's really a definition thing that defines how long something is stable while in-flight.
In the case of a long skinny bullet, is it possible that the bullet goes thru a critical speed where it bends only to become straight again once passing thru that critical speed? Granted, a bullet is an extremely short and fat shaft. But gotta wonder if there is a critical speed for a long skinny bullet.
Just had to do it 
The spin of a bullet changes very little in flight. Too fast a spin and the mechanical strength of the bullet can cause it to poof. If CG is NOT on axis, you can get wobble. Wind can increase yaw angle and induce instability. Understable is a misnomer also - once unstable who knows what it will do. The equation we use just gives the ratio of the 2 momentums to imply it SHOULD be stable.
The spin of a bullet changes very little in flight. Too fast a spin and the mechanical strength of the bullet can cause it to poof. If CG is NOT on axis, you can get wobble. Wind can increase yaw angle and induce instability. Understable is a misnomer also - once unstable who knows what it will do. The equation we use just gives the ratio of the 2 momentums to imply it SHOULD be stable.
F
freebullet
Guest
CZ93X62
Official forum enigma
Before spoiling the chamber in my flatband Win 94 with dacron fiber, I ran a little experiment with its barrel (25/35 WCF caliber) and its 1-8" twist rate. I had a number of 25 caliber moulds on hand, and ran up against a DEFINITE speed limit with the NEI 114 grain flatnose GC design in this 1-8" twist. The rifle had delightful accuracy up until the 1600 FPS level--once past that speed, the groups "Went 12 gauge", and not even full-choke. I tried two shorter bullets at same sizing (.260"), Lymans #257420 and #257312; same result--decent to 1600 FPS, then groups went galley-west. I tried a plain-base just for grins, the RCBS #25-85-CB; it was accurate to about 1000 FPS, past that point it was ridiculous. (Note--this same bullet in my Marlin 94 [25/20] shoots very well to 1400 FPS). I don't have the background to opine the wherefores and whys of this--I just know it happened. SOMETHING causes this to occur.
This is part of “too fast a twist rate”. In this context they are talking rifles intended for use as sniper rifles in the 1000 plus yard range as an alternative to the 50 BMG.
My understanding is that it also explains why part of why Palma rifles often use a 13” twist rate with a 155 gr bullet. Goal it to keep the nose pointed in the direction of bullet flight, not nose up even as the bullet descends.
This has little bearing on shooting at ranges we normally use. One of the biggest problems with shooting sports is taking something from one discipline where it matters and assuming it matters in all other disciplines.
My understanding is that it also explains why part of why Palma rifles often use a 13” twist rate with a 155 gr bullet. Goal it to keep the nose pointed in the direction of bullet flight, not nose up even as the bullet descends.
This has little bearing on shooting at ranges we normally use. One of the biggest problems with shooting sports is taking something from one discipline where it matters and assuming it matters in all other disciplines.
Snakeoil
Well-Known Member
This is an interesting tangent. When I was shooting BPCR, I shot with a gentleman who won the senior class at Raton the year he went. He was a retired artillery Colonel in the Army. There were always discussions at the range because of the broad range of knowledge amongst the shooters (like me as a newbie and others like Dave Hicks and Don Hamilton that forgot more than I'll ever know) and a point Adrian made was that a projectile's nose does not arc a shown in the first curve, but rather flies as shown in the third curve. The vast amount of the basis for his statement was artillery rounds. I always had assumed the 1st curve applied in all things from simple experience like water rockets as a kid.
I understand the point here. If the bullet travels with an attitude based upon how it leaves the barrel, the aerodynamics change as it reaches the apex of the arc and begins to descend. I would assume there is a reduced pressure on the top side of the bullet making it want to flip over as shown in the second curve. But, does not the equal pressure about the nose tend to keep it aligned with the flight path? Or is the spin sufficient to keep it from tipping, similar to what you would experience holding a gyroscope in your hand and trying to tip it.
Needless to say, I'm not very well informed on this subject. I'm trying to put into simple terms as I am understanding it. I have to admit that when you start talking about angular mass and ratio of two momentums, you are losing me simply due to ignorance on my part. Probably need to start reading that precision long range shooting book so I can keep up.
Getting back to CZ's experience with his '94 Win., my limited knowledge on the subject would have me thinking that the twist rate was too fast for the bullet speed and the alloy strength of the bullet and he was shearing thru the lands and a very torn up bullet was leaving the muzzle.
I'm also curious about is ruined chamber (I suspect ringed) due to Dacron wad. I'd have to ask what did you do wrong, CZ. Not to find fault, but to understand better the pitfalls of fillers. There are so many opinions on either side that there might as well be no opinions. But data speaks volumes, if available.
I understand the point here. If the bullet travels with an attitude based upon how it leaves the barrel, the aerodynamics change as it reaches the apex of the arc and begins to descend. I would assume there is a reduced pressure on the top side of the bullet making it want to flip over as shown in the second curve. But, does not the equal pressure about the nose tend to keep it aligned with the flight path? Or is the spin sufficient to keep it from tipping, similar to what you would experience holding a gyroscope in your hand and trying to tip it.
Needless to say, I'm not very well informed on this subject. I'm trying to put into simple terms as I am understanding it. I have to admit that when you start talking about angular mass and ratio of two momentums, you are losing me simply due to ignorance on my part. Probably need to start reading that precision long range shooting book so I can keep up.
Getting back to CZ's experience with his '94 Win., my limited knowledge on the subject would have me thinking that the twist rate was too fast for the bullet speed and the alloy strength of the bullet and he was shearing thru the lands and a very torn up bullet was leaving the muzzle.
I'm also curious about is ruined chamber (I suspect ringed) due to Dacron wad. I'd have to ask what did you do wrong, CZ. Not to find fault, but to understand better the pitfalls of fillers. There are so many opinions on either side that there might as well be no opinions. But data speaks volumes, if available.
Great visual Brad. Unfortunately, #1 never happens (well it does for slow fps/twist nose heavy arrow). #2 happens at the terminal end. Getting back to the transonic region, the velocity direction (vector) follows the path in #3. Force of air is exact opposite. Base has more surface area therefore more force exerted on base than nose and (as #3 shows) nose tilts up. This yaw angle change acts on the spin momentum to force the nose 90 deg (gyro action)horiz. to path. The nose up also changes the pressure (shock) ridges ON the bullet changing path more. Very complicated and hard to predict results in transonic region.
RBHarter
West Central AR
Proximity , timed , and detonation fuzes .
The big guns have used all 3 sometimes all 3 in a single fuze train rotationally armed . And I just deleted toooooo much information ...
Proximity fuzes use an atmospheric switch that sets or trips at a given speed or altitude . Think of air burst shells with high trajectory .
Timed fuzes are pretty obvious . Typically hand grenade types but useful in long range shells where a flight time can be watched on a wall clock say 50 miles with an MV of 2700 fps and a BC over 4.0 (someone gave me that number years ago on CB) . A time fuze in such could be set for 10-12 even 15 seconds in the case of a penetration type round to go off "well after" impact .
A detonation type has a 270° sphere at x ftlb non directional impact firing arrangement . After firing it is 360°² so the shell can hit in any attitude and as long as X ftlb of impact force is present .....poof .
The big guns have used all 3 sometimes all 3 in a single fuze train rotationally armed . And I just deleted toooooo much information ...
Proximity fuzes use an atmospheric switch that sets or trips at a given speed or altitude . Think of air burst shells with high trajectory .
Timed fuzes are pretty obvious . Typically hand grenade types but useful in long range shells where a flight time can be watched on a wall clock say 50 miles with an MV of 2700 fps and a BC over 4.0 (someone gave me that number years ago on CB) . A time fuze in such could be set for 10-12 even 15 seconds in the case of a penetration type round to go off "well after" impact .
A detonation type has a 270° sphere at x ftlb non directional impact firing arrangement . After firing it is 360°² so the shell can hit in any attitude and as long as X ftlb of impact force is present .....poof .