Asymmetric and Unbalanced Bullets

[colt 357]

Dont know if this video has been posted but found it to be very interesting. This guy is shooting bullets that he filed to be off balanced then shot them on high speed camera. Makes me wonder if I am being to picking when inspecting my cast bullets your thoughts guys looking forward to what you guys think about this.

https://www.youtube.com/watch?v=C9Dylxy3zJc

[btroj]

To see the bullet corkscrew in flight tells you much.

[triggerhappy243]

I watched the video and my question to you would be how bad are your cast bullets and secondly what are your intentions for your cast bullets? I shoot cast because besides the propane and my lead, all else was free. i shoot just plinking. so they are not intended for match accuracy at this time. still have not tried accuracy tests. all in good time.

[pretzelxx]

I like how he got the flat to curve upward, that was cool to see

[Larry Gibson]

To see the bullet corkscrew in flight tells you much.

Too bad the pundits of the RPM threshold don't watch this and understand what the helical arc in flight is (the "corkscrew"). They also might take note of how imbalances adversely affect the bullet in flight. The .22LR rounds used had a low RPM to begin with. The RPM threshold was lowered by the severe unbalancing of the bullets so even at that low level of RPM the effect is dramatic. Imagine the increase in RPM if we double the velocity and deacrease the twist from 1-16 (maybe 14") in the test rifle to 10" twist or faster?

Larry Gibson

[rhead]

While it is in the barrel the bullet is forced to spin around the center of the bore. Once it leaves the barrel it will begin to try to spin about its center of mass.

A cast boolit cools and becomes solid from the outside in so there will be an area of lower density somewhere near the center of the boolit. the closer to the center this area is the more accurate the boolit will shoot.

Does a boolit cast from a single cavity mould show more accuracy than a boolit cast from a double cavity mould? I do not own a both single and double cavity mould of the same boolit and probably cannot shoot well enough to see the difference. This is conjecture. has anyone ever tested this. Some of the skilled match shooters should know if (on average) do single cavity moulds preform better than double cavity moulds (which should cool faster from the sides than they do to the end).
If the area of lower density was on the outside the upset should be multiplied.

[Garyshome]

Great video!

[JimA]

Surprising accuracy for some of those bullets. The flat "curveball" was cool.

[Wayne Smith]

Dr. Mann did much more. Damage the base and see what happens! Or read his book, The Bullet's Flight.

[jonp]

Too bad the pundits of the RPM threshold don't watch this and understand what the helical arc in flight is (the "corkscrew"). They also might take note of how imbalances adversely affect the bullet in flight. The .22LR rounds used had a low RPM to begin with. The RPM threshold was lowered by the severe unbalancing of the bullets so even at that low level of RPM the effect is dramatic. Imagine the increase in RPM if we double the velocity and deacrease the twist from 1-16 (maybe 14") in the test rifle to 10" twist or faster?

Larry Gibson

My first thought was the relationship between the off balance corkscrew and rpm of the projectile. Larry, in assuming the RPM is low are you making a general statement about the velocity and an average barrel twist for a 22 rifle? Also, that the rpm will always be lowered by the aerodynamics of the projectile due to drag?

rhead: "A cast boolit cools and becomes solid from the outside in so there will be an area of lower density somewhere near the center of the boolit"

Can you explain this a little more rhead without getting too technical? Do you mean that your melt is of uneven density and the most dense lead migrates naturally towards the outside? Considering how quickly the boolit cools into a solid state the chance of the melt to become uneven in cooling is very small and it will not change much. Hardness and Density are not the same thing. Are you using slang to make a point about how a boolit reacts?

[45 2.1]

Too bad the pundits of the RPM threshold don't watch this and understand what the helical arc in flight is (the "corkscrew"). They also might take note of how imbalances adversely affect the bullet in flight.

This is actually funny, coming from you. We have observed... We do know what is happening... We also know how to cure that problem and have done so.

Here is how:
1. We reduce tolerance stack.
2. We do not shoot substandard dimensioned boolits, especially ones you use.
3. We pay no attention to the use of any 4895 powder or dacron.
4. We use a properly proportioned alloy suitable for the pressures involved.
5. We shoot boolits that actually fit the firearm that aren't undersized.
6. We load them to the required pressure level so they shoot properly.
7. etc.

All the effects you've noted occur with match jacketed bullets also.... and some of them shoot very tiny groups at long range, just like a good boolit does. You might want to look at a BP match grade boolit in flight from muzzle out to about 600 yards and see what it does, you might learn something there.

[C. Latch]

Could someone fill me in on the nature of the RPM threshold feud?

I'm kinda new and must have missed the roots of this one.

[45 2.1]

Could someone fill me in on the nature of the RPM threshold feud?

I'm kinda new and must have missed the roots of this one.

It is fairly old now.... and I'm sure that someone will say something else about it. The crux of the matter is that the poser of the theory says you will have trouble with unbalanced boolits above a certain RPM (which can be true if you use substandard equipment toleranced incorrectly and you make some decisions so the boolit has plenty of room to get booted out of line with the bore). He has proposed you can "push" it if you have your ducks in a row OR you can use a slow twist barrel to alleviate it somewhat. While the second is true (and reduces the firearms use for other things), the first is just a wrong assumption caused by other tolerancing factors which have been brought up several times by me and others. Now, lets see if this is succinct enough.

[C. Latch]

It is fairly old now.... and I'm sure that someone will say something else about it. The crux of the matter is that the poser of the theory says you will have trouble with unbalanced boolits above a certain RPM (which can be true if you use substandard equipment toleranced incorrectly and you make some decisions so the boolit has plenty of room to get booted out of line with the bore). He has proposed you can "push" it if you have your ducks in a row OR you can use a slow twist barrel to alleviate it somewhat. While the second is true (and reduces the firearms use for other things), the first is just a wrong assumption caused by other tolerancing factors which have been brought up several times by me and others. Now, lets see if this is succinct enough.

Thanks for the explanation. I keep seeing this pop up in various threads (some new, some older ones that I find in searches) and couldn't figure out what the big fuss was about.

[jmort]

I too was surprised by how accurate the " unbalanced" bullets were and that the uneven flat cut was "worse" than the others.

[Larry Gibson]

It is fairly old now.... and I'm sure that someone will say something else about it. The crux of the matter is that the poser of the theory says you will have trouble with unbalanced boolits above a certain RPM (which can be true if you use substandard equipment toleranced incorrectly and you make some decisions so the boolit has plenty of room to get booted out of line with the bore). He has proposed you can "push" it if you have your ducks in a row OR you can use a slow twist barrel to alleviate it somewhat. While the second is true (and reduces the firearms use for other things), the first is just a wrong assumption caused by other tolerancing factors which have been brought up several times by me and others. Now, lets see if this is succinct enough.

C.R. Latch

45 2.1's explanation is wrong which is why there is a continuing "feud" as such. 45 2.1 just doesn’t understand that when he says; “The crux of the matter is that the poser of the theory says you will have trouble with unbalanced boolits above a certain RPM (which can be true if you use substandard equipment toleranced incorrectly and you make some decisions so the boolit has plenty of room to get booted out of line with the bore)" that it is absolutely true for 90+ % of rifle bullet casters and shooters. As long as they use regular cast bullets of regular ternary alloys loaded with standard equipment using standard loading procedures their loads will bump into the RPM threshold, generally in the 120,000 to 140,000 RPM range. So when one of those 90%+ ask why they lose accuracy at a certain velocity I explain it to them. The explanation is correct as it pertains to their load. 45 2.1 goes into a nut roll and says it isn't so......problem is he has just admitted it is so. The RPM threshold does exist. He, simply by what he says as we've seen no groups or even photo's of proof of his posted, apparently is adept at pushing the RPM threshold upward. He uses all of the techniques I have stated are necessary for many years on this forum. I assume he is successful as I am but he adamently refuses to demonstrate such to many of us. None the less let us continue.

A simplified definition of the RPM threshold is; “The RPM threshold is that point where accuracy begins to deteriorate when the RPM is sufficient to act on imbalances in the bullet in flight to the extent the bullet begins a helical arc in flight or it’s flight path goes off on a tangent. It is best noted when working up a load as velocity increases flyers begin to happen. Then as velocity is further increased the total group size increases sometimes to the point some bullets fly so far off they miss the target. A further indication the cast bullets at or over the RPM threshold is (or some of them in a load that is on the edge of the RPM threshold) the non linear dispersion of the group size as range increases.” A more detailed explanation is found in the sticky; http://castboolits.gunloads.com/show...velocity-chart

45 2.1 continually post untruths about what he thinks I believe and say. So let’s take a look at what his untruths are in this thread as he posted them. I will tell you what I really think and say in answer to each of his "talking points".

1. We reduce tolerance stack.

Unknown what he means by this(?) but assuming he means consistency of loading procedures and equipment so the bullet, cartridge and components along with the rifle are consistent and aligned. Truth is I consistently provide real information as to all this. If one is to push the RPM threshold up then tolerances of the bullet, the cases, the components and the rifle must be as close as we can make them. With factory and milsurp rifles we are pretty much stuck with the way they are assembled as far as tolerances. With custom rifles we are not and can make them to as close as tolerance as possible. With custom rifles we can also pick a rifling twist more conducive to keeping the RPM under the RPM threshold to begin with for cast bullet use at higher velocity.

2. We do not shoot substandard dimensioned boolits, especially ones you use.

45 2.1 continues to offer this untruth. I do not use “substandard dimensioned bullets”. I used a standard 311291 in one test to prove a point. The point was proven. That mould does not produce a nose diameter that “fits” most .30cal bores. Thus 45 2.1 continually used that example of my “substandard dimension bullets” even though I used it intentionally. He ignores the fact that I go to great lengths to ensure proper fit of the bullet to the case neck, the throat and the bore. He ignores I advise to keep the bullet concentric to the bore. He ignores the fact I consistently say if the RPM threshold is to be pushed up a bullet of proper design is needed. Then worst of all he ignores that I use several of his own designed bullets to push the RPM threshold up. Ponder his; if I am using "substandard dimensioned bullets" (I always give the sizing I use in my test reports) then how is it I shot a sub moa 10 shot group at 100 yards at 2600+ fps with a 311466?

I also posted photo’s of 6.5 Kurtz bullet (his design) that were sent to me by a person we can not mention here. The photo and post were deleted by a moderator. These 6.5 Kurtz bullets were sent to me to test by the unmentionable. 45 2.1 posted numerous times of the marvelous accuracy these bullets produced at very high velocity/RPM when shot by the unmentionable. Most of those bullets were rejects by my standards of properly dimensioned cast bullets. They shot very poorly BTW. Thus it is obvious that 45 2.1 and I do have a very different idea of what “substandard dimensioned bullets” really are.

In order to push the RPM threshold up your cast bullets of a ternary alloy must be of consistent dimension and consistent weight. They must fit the case neck, the throat and the bore. They must be loaded concentric to the bore. That is the truth.

3. We pay no attention to the use of any 4895 powder or dacron.

What this has to do with pushing the RPM threshold up is anyones guess? The truth is I almost always recommend a slower burning powder for use in pushing the RPM threshold. Most often I recommend the use of AA4350, RL19, H4831SC and RL22. Those all meter well and they ignite and burn efficiently at lower psi’s of 28,000 to 40,000+ psi’s. They offer a slower time/pressure curve to lesson the unbalancing of the cast bullet during acceleration. I measure the actual pressure and see the time/pressure curve of numerous cartridges in 30+ firearms BTW. All of the powders I recommend most often have an 80%+ load density and do not need a dacron filler nor do I recommend one for those powders with loads that are pushing the RPM threshold.

My recommendation of 4895 powder and the use of a dacron filler has nothing to do with pushing the PM threshold. The truth is; the recommended use by me of 4895 with a dacron filler has to do with standard loads under the RPM threshold. The dacron filler simply holds the owder in position against the primer consistently allowing for consistent ignition and burning of the powder at the lower psi's (usually under 28,000)reducing the extreme velocity spread of the load. That most often simply improves accuracy below the RPM threshold.

4. We use a properly proportioned alloy suitable for the pressures involved.

Yes we do. As mentioned by me in almost any thread of this topic the RPM threshold can be pushed up or down by hardening the cast bullet through heat treating or annealing and change in alloy by hardening or softening with the addition of additional lead or copper for example. If you want to push the RPM threshold up then hardening the bullet is needed. I use a heat treated ternary alloy and BadgerEdd’s copper alloy for the highest velocity/RPM loads. Though I have pushed the 311466 of ternary AC’d alloy to 2600 fps with sub 2 moa accuracy out of my 14” twist Palma rifle and to 2400+ fps out of my 12” twist M70 Target rifle. Out of my 10” twist pressure test rifle accuracy goes over 2 moa at 2100 fps. Those are all .308Ws and the tests are with 10 shot groups at 100 yards.

With the hardened alloys I am pushing 2750 fps with 2 moa accuracy using the 311465. I also shoot the MP 311-180 (one of 45 2.1s designs) to the full potential of the .308W in both the 12 and 14” twist rifles at 2400+ fps.

5. We shoot boolits that actually fit the firearm that aren't undersized.

45 2.1 sure is stuck on that one, eh?

6. We load them to the required pressure level so they shoot properly.

As do I and anyone else who pushes the RPM threshold. The “required” pressure level is needed for efficient burning of any powder. All powders have a “required pressure level” before they burn efficiently. The faster burning powders burn efficiently with as low as 7 - 8,000 psi and the slowest require upwards of 40,000+ psi to burn efficiently. The trick is to use the right slower burning powder that gives 80%+ load density, that burns efficiently and that gives the slowest time/pressure curve to push the RPM threshold up.

7. etc.

Looks like 45 2.1 ran out of untruths and has already repeated the “fit” one………it is unfortunate 45 2.1 doesn't pay close attention to what he said in this thread (I posted it in this post above) as he does actually agree with me. However, he made his bed and is insistent on sleeping in it I guess.......thus the "feud".

So C.R. Latch I would invite you, if you are interested, to look at what I’ve posted here and really posted on the other threads relating to the RPM threshold. Look at the tests I’ve done, the target groups I’ve posted and my willingness to demonstrate such by going shooting with you, 45 2.1 or anyone else. If you shoot cast bullets in rifles and have worked up a load and found the accuracy went south at a certain velocity simply convert that velocity to RPM and you will find the RPM threshold.

Larry Gibson

[Idz]

So how much of the corkscrew is caused by the off center weight and how much is due to the totally screwed up aerodynamics? Did Mann separate the effects by drilling out an off-center core of lead and then plugging it with plastic or something?

[mrbill2]

Well C. Latch now you went and done it. You had to stir the pot, didn't you. Here we go again. Which came first, the chicken or the egg?

[C. Latch]

I certainly learned a bit today.

In all seriousness, my interest in this would be academic, not practical; unless I get a wild hair to shoot my '06 a lot and start stuffing my 30-30 boolits into it, I'll probably never launch a cast projectile faster than 2000' to 2200' MV. Right now most of my shooting is .45 Colt and .45 ACP. That's not to say that the argument above isn't worthy - physics is fascinating stuff and well worth learning - it's just, honestly, more than I can chew on at the moment.

[45 2.1]

Well C. Latch now you went and done it. You had to stir the pot, didn't you. Here we go again. Which came first, the chicken or the egg?

Awww, mrbill2....... Larry sure does go on a tear on those long posts trying to convince folks he is right. He has done the same thing on more than one forum about that video and gotten his backside handed to him, some of it by people from here. I think C. Latch and others can make up their own minds about this nonsense from what is written here.