Bullet stabilization

[Cuts Crooked]

One good way to get a grasp of this is to watch someone shooting BP with a wax disc under the slug, but no card wad. Saw this at a match several years ago. Female shooters significant other made up her BP 44-40s that way and you could watch the smoke trails spiral into the targets. Looked like there was no way in He!! that she was going to hit the 50 yd steel, but she did every time!

[Drydock]

Once the bullet exits the muzzle, it has to react to a whole new enviorment.  It is also pushed sllightly off center by gas acting on its base as it exits the muzzle.  The gyroscopic force of the bullets rotation counteracts this, so the initial trajectory has the bullet seeming to orbit a point outside its axis as it goes down range.  This axial "Point" coincides with the desired trajectory in a well aimed shot.

 As the bullet stabilizes, and equalizes the atmospheric forces acting upon it, gyroscopic precession causes it to tighten its "orbit" around the axial point until it falls within the bullet itself.  THus the bullet seemingly comes back on trajectory.  It has always been on trajectory, but simply "Orbiting" around it until full gryroscopic stabilization occurs. 

(You could REALLY see this on the 16"/50 battleship guns I got to watch a few times in my career.)

[Delmonico]

And not to sound like a smart arse, but it's plain to see that some of us understand this and how it happens.  Heck if you have fresh cast bullets and shoot away from the sun on a bright day you can see the bullet do this if you have good eyes.

[Advertising]

[Fiddler Green]

Once the bullet exits the muzzle, it has to react to a whole new enviorment.  It is also pushed sllightly off center by gas acting on its base as it exits the muzzle.  The gyroscopic force of the bullets rotation counteracts this, so the initial trajectory has the bullet seeming to orbit a point outside its axis as it goes down range.  This axial "Point" coincides with the desired trajectory in a well aimed shot.

 As the bullet stabilizes, and equalizes the atmospheric forces acting upon it, gyroscopic precession causes it to tighten its "orbit" around the axial point until it falls within the bullet itself.  THus the bullet seemingly comes back on trajectory.  It has always been on trajectory, but simply "Orbiting" around it until full gryroscopic stabilization occurs. 

(You could REALLY see this on the 16"/50 battleship guns I got to watch a few times in my career.)

So, your'e saying that a bullet that is just over one inch in length, that is4" off POA is going to come back to 2" of point of aim a 200 yards?

Bruce

[Delmonico]

It sure does, that is obvious by the groups tightening up at distance.

As I said eariler this effect is lessened by the more perfect the bullet is.  The base being perfect is very important, one reason many over the years have prefered either a nose pour bullet or a swaged one.

Also voids in the interior that are only known to be there by weighing and finding them to come up short has a big effect, depending on the size and how far they are away from center.  One needs to find the max standard for bullets with perfect looking bases and remembering a perfect bullet on the outside will not go over weight, one needs to decide a standard one will not shoot an under weight bullet. weighed before it is lubed.

My standard on mine is 509 grs with my alloy and my mould.  Nothing under 1/4 grain below that is ever shot,and with perfect bases, do not go over, those which don't meet the standard are recast.  You never mentioned your standard although you have told us many times you have shot a lot of bench rest.  My deviation on the closer shots tightened up a lot when I set this standard and pretty much now shoot groups at closer range as tight as the further range.

[drcook]

What has been very technically described is part of the ballistic curve. The other parts of the ballistic
curve deal with the physical effects of gravity on the projectile.

It's the effect you see when tuning a black powder load. A "circular pattern" (horizontal and vertical
string aside, these are caused by other issues) is what you  get on the target. As the load is tuned
the size of the "circle" - "coned corkscrew" thru time and space diminishes until a balance of
velocity and other variables is achieved.

We just see the effect more in this kind of rifle because the mass of bullets we use is larger and the
velocity slower than say a .223 or a .243 or a .30-06. Ballistics conform to the laws of physics, and
that is what is being described. The projectile from naval ship as described above, dramatically hilites
the effect because the mass of the projectile is so much greater than a 45 caliber bullet.

You can also the visulaize the effect being described in a curve ball thrown by a major league pitcher.
The spin imparted on the baseball causes it to fly in an arc. A gifted pitcher has learned to control
velocity and rate of spin and release point etc so that the ball just catches the edge of the target
(ie: the plate).

If a person really wanted to compound the discussion, we could bring in the effect of either a right
hand twist -vs- a left hand twist -vs- the rate of twist -vs- whether you are shooting in the northern
or souther hemisphere.  The earth itself, and its gravitation field affects the trajectory of a bullet, the
same way that water spins one direction in the northern hemisphere and the opposite in the southern
when going down a drain, ie: the water spinning in the toilet when its flushed.

Also what must be taken into consideration with these old rifles is the so called "null spot" on the
barrel. The barrel will ocillate and if not on the crosssticks at the null point, (assuming you are
shooting from sticks or a rest and not offhand) the bullet will exit the barrel on one of the waves.
Also if shooting off sticks, and the same point is not utilized, the bullet will exit the muzzle in a
different point of one of the waves, causing the groups to be bigger.

Velocity variations will also exaccerbate the "orbitting" or "corkscrew" effect the gentlemen above were
technically describing. That is why people who shoot BPCR matches strive for single digit EV's.

Regardless of how the process is described, very technically or in a plain manner, a balanced load, using
components that match (as Delmonico is so correctly emphasizing) with sufficient velocity to impart the
gyrosopic effect described above, will impact a target in the same place regardless of distance because
the bullet is acting the same, shot to shot to shot.  I know of a college professor who tunes his loads
using statistical analysis methods to achieve the shot to shot consistency.

You can visualize what happens to a bullet that has a void by thinking about the washing machine
that gets too many clothes on one side and the washing machine starts to walk across the floor
 instead of spiinning with no vibrations. A bullet that is ligher will have a higher trajectory and a heavier
one, of course the opposite.

Which gets back to the original question/thought/theory that the guns are more inherently accurate
at longer ranges over the shorter ramges, and I still maintain that they aren't. It's simply the effect of
a load that has not been tuned in. Otherwise there would be a bunch of folks in the BPCR crowd,
gong shooters, etc, who would not be shooting as good as they are, at all distances. Some of those
folks out west are doing phenominal achievements with these types of guns. And I shoot with a bunch
of folks on a short course BPCR range (100, 150, 210 and 235) who maintain consistent accuracy at
those ranges, month to month.

There are other variables that are going to effect percieved accuracy. Some of the BPCR folks have
switched to paper patched bullets and wiping between each shot, striving to maintain the shot to
shot consistency so that the bullets act in the same way as has been described above. Kenny
Wasserburger (from over at the Shiloh board) shoots paper patch bullets, up to a mile away, but he
also shoots at shorter distances also. I believe he recently shot 5 in 1 3/16" at 200 yds for a new
record.

dc

[Drydock]

Take a football, set it on its side, and spin it. If you do it right, and spin it fast enough, see how it ends up?

[Fox Creek Kid]

The two most important parts for bullet stabilization are:

A. Bullet length in relationship to twist rate.

B. When the bullet goes sub-sonic again downrange.

Bullet weight is basically irrelevant as it's mass, not weight that is involved here. Weight is just the method we use today. Select the best bullet for your twist rate. As far as sub-sonic concerns, worry about that when you can hit something past 500 - 600 yds.

[Drydock]

Now boys, play nice.

The most accurate bullet, all other things being equal, will be the one with the best distribution of mass around the desired axis of rotation.

[drcook]

The most accurate bullet, all other things being equal, will be the one with the best distribution of mass around the desired axis of rotation.

That is why Paul Jones' and Steve Brooks' moulds are used to cast superb bullets. I have a 540 gr PJ Creedmore
mould here at the house, and moulds from Steve Brooks in various calibers and weights. Recently Buffalo Arms is
starting to bore moulds on a CNC lathe and I have a 510 gr Creedmore mould from them and are a good buy
for the money.

Hoch nose pour moulds cast good bullets, with superb bases, but are a little harder to get casting correctly.
Temperature is critical on a nose pour mould. I now heat them up over the gas burner in the kitchen set on low
to help get them up to temp without having to cast 20+ bullets.

I have a Steve Brooks mould that I acquired when I bought a rifle. The rifle was in better shape than the mould
to say the least. I was able to drill out the frozen mounting screw and get it to line up better. It still sometimes
casts fins on the bullets where it appears to have been tried to lap it out a little.  HOWEVER, it still makes a
decent bullet and I have decided to send a sample back to Steve and have him make me a new one. It casts
a 513 gr Creedmore bullet. I really like it for my 45-70's.

I use electronic earmuffs and you can hear unstable bullets. They sound like a hornet buzzing. At Sagebrush's
match in Alliance Neb, we were able to hear someone's unstable bullets even without the use of electricon muffs.

Lately a group of people that I am acquainted with are really moving towards the paper patched bullet for the
utmost in accuracy. I guess I am going to have to try that next. You have to wipe the bore between each shot
though.  They are also (courtesy of Dan Theodore, amongst others) working on the nose profiles to create a
more aerodynamic bullet that deals with the time above, below and the transition through the sonic barrier.

Rick Mulhern shot this one at 1000 yds using a paper patched 50-90.  ALSO needless to say, as I have been
saying in my different posts in this thread, I and no one that I know, ascribe to the statement that these rifles
are not as accurate in the shorter ranges as they are at distance.

Click on the pic and it will take you to a larger version.

dc


   

[Angel_Eyes]

I have just read the whole of this argument discussion, and have come to the conclusion that you are all correct in the majority of details that you have all put forward.
The one thing that has only been mentioned in passing, is the supersonic to subsonic transition.
I have encountered this in both B/P cartridge shooting and Nitro loads.
As near as I can determine FG's load is right in that transition period at 100 yds!!
If you are only shooting that distance, my advice would be to try and keep it subsonic, and see how that works out.
Use your original load for longer distance's.

My B/P loads grouped better at 500yds than my nitro loads out of my Pedersoli Sharpes.

Regards to you all, AE

[Ranch 13]

270 yds.
 Also take a look at this years Quigley results. #126. Target 1 buffalo 789 yds, 2 stop sign 600 yds, 3 rectangle 531yds, 4 diamond (12 inch square)380 yds, 5 square 411, 6 bucket (22 wide at the top, 18 at the bottom, about 30 in deep) 350 yds off hand.
 
Now how much weight variation does Bruce allow between bullets? simple question, should be simple answer.

[Drydock]

We've explained transonic buffeting, we've explained gyroscopic precession, we've even gone into orbital mechanics.  If you do not comprehend the basic physics behind rotating ballistic objects, then no explanation given here will suffice.  Accept it and move on.

I would suggest you read this:  http://en.wikipedia.org/wiki/Precession

[Delmonico]

He sure seems to avoid the question of his weight standard and keeps repeating what he has said before and avoids the question. 

[Ranch 13]

We've explained transonic buffeting, we've explained gyroscopic precession, we've even gone into orbital mechanics.  If you do not comprehend the basic physics behind rotating ballistic objects, then no explanation given here will suffice.  Accept it and move on.

I would suggest you read this:  http://en.wikipedia.org/wiki/Precession

 Well here's what I've come to know about this deal, and purt neart all of it came from range time both as a shooter and a spotter at distances from 200-1000 yds.
 1. If a bullet won't group at 100 yds it sure won't group at 500 or anyplace inbetween. Unless A: the sight inserts don't allow for a good sight picture at 100, or B shooting technique gets fouled up when shooting the 100 yd group.
 2. As we weren't allowed any group sizes or what targets or what conditions were when this anomaly happened, my experience tells me that the transonic deal isn't into play here. When these big ol hunks of lead loose stability they're gone of to wherever they may be  headed and 9 times out of 10 it doesn't have anything to do with the target they were fired at.

 I've watched bullets in flight and there are times when all looks well right up to the target and then they just drop like a rock. I've watched in dissappointment as a young man that had been shooting almost perfect scores at 3,6 and 800 yds couldn't of hit the target at 900 and 1000 if he'ld of been setting on them. What happened was his 61 grs of swiss and the 500ish gr bullet ran out of stability somewhere past 800 yds. And you could see them in the spotting scope as they came into view at both the 9 and 1000 yd targets, it looked like they were riding a circular staircase.
 Also its not hard to tell which shooters have just fired bad bullets on the line as the unmistakable sound of a mini helicopter going down range, and flops of dust coming up who knows where maybe close to the target , maybe not.
 There's a plenty of things that could be going on with Bruce's loads here but bullet stability at the relatively short ranges he's shooting at isn't the problem

[Delmonico]

As I said, I allow 1/4 grain over or under the standard of 509 for the bullet I use.  When I went to doing that I have no unexplained fliers.  Also the groups stay tight from the get go. 

[Ranch 13]

 I play a little more fast and loose with the weights. I'll go 1gr +- of the zero point. The rcbs 82084 comes in at 532 from 20-1.
 Dan Theodore said a while back on one of the boards that as long as the bullets "match quality" a 3 gr difference didn't show up for him during some 1000 yd testing.
 With that said tho keeping everything close is a real good idea.

[Delmonico]

I play a little more fast and loose with the weights. I'll go 1gr +- of the zero point. The rcbs 82084 comes in at 532 from 20-1.
 Dan Theodore said a while back on one of the boards that as long as the bullets "match quality" a 3 gr difference didn't show up for him during some 1000 yd testing.
 With that said tho keeping everything close is a real good idea.

I've been told mine is overboard but when things are running good I only reject about a 1/4 of them for visible defects or weight.

[Ranch 13]

Oh I don't think what you're doing to be that overboard, the majority of the bullets I cast after the mold and melt get to running smooth fall in that close, I'm just to lazy to throw the ones that don't make it that tight back and do them over. That's why I allow the 1 gr .
 Going to get one of the Cabine Tree mold handles, lots of folks have plenty of good things to say about them. Seems the way they lock down the same everytime, they make for some awfully consistant bullets.

[Drydock]

Well, he was asking why some loads will appear to be off trajectory at relativly close ranges, yet be back on trajectory further down range.   Transonic buffeting combined with gyroscopic precession is the answer, as most BP loadings go transonic in the 100 to 200 yard range.