Trailing Edge and accuracy

[Bama]

Hope to get some discussion and enlightenment. I have always read about the importance of a good barrel crown for an accurate rifle. The question is " Is the trailing edge of the Bullet which should be just the reverse of the crown as important as the barrel crown?" Has anything been done in the past to enhance or improve the trailing edge to improve accuracy other than adding a gas check?

[ascast]

I am not sure what you mean by "reverse of crown" but bullits have bevel base, boat tail, and nose pour and adding a few wads to improve accuracy.

[JBinMN]

I would say that it does. Look at "boat tail" bullets. They are designed so the trailing edge of the bullet has low drag. That is just one example of the shape of the base having an effect on the speed & accuracy. So, IMO, the base of bullets, and particularly cast boolits should be inspected just as much for imperfections as well as the rest of the boolit. Seems to me that a bullet that has a chunk missing on the base wile also have an effect on it when flying thru the air due to it being out of balance & an effect on the drag/B.C. I am not expert though, just using what I thought would be a comparison to help with your question. I think it does have an effect.
:)

[country gent]

Casting your bullet and maintaining a sharp square clean edge is one. Rounded edge or dinged up can have a detrimental effect same as a bad crown. Even the bevel base if not true and clean can cause problems. A mould that casts a square true clean base is a big plus. This is one reason for nose pour moulds, bases are square and done correctly the base is sharp as a knife edge. I modified a 535 grn 45 cal lyman postell mould from base pour to nose pour. Accuracy improved compared to bullets cast with the same mould before converting. Bases looked like glass on the bottom no sprue marks or imperfections Base appeared slight more square on the comparator and edges were very sharp and crisp, compared to the ones cast before. The conversion took away a little of the radious on the nose for a small flat. Was an interesting experiment on this mould.

[kens]

in muzzleloading round balls, we know that it is more important for the base to be perfect rather the nose.
I dont know why. But we know if the base is chewed up they wont group. But if the nose is chewed, it dont matter as much.
That is why we load with the sprue on top.
No doubt a similar thing exists with bullets.
I would imagine that a skewed base would have uneven gasses exiting the muzzle

[runfiverun]

http://castboolits.gunloads.com/showthread.php?120735-Cast-bullet-accuracy-and-trailing-edge-failure

[JBinMN]

http://castboolits.gunloads.com/showthread.php?120735-Cast-bullet-accuracy-and-trailing-edge-failure

Thanks for that link.
:)

Good read!

[725]

Good crown and good bullet base are very important for accuracy. Irregular gas escape at the point of bullet departure from the muzzle will induce a yaw in the bullet flight and adversely affect accuracy. Recut your crown if there are dings or worn sides and cast good boolits. The two work in tandem towards good accuracy.

[OS OK]

http://castboolits.gunloads.com/showthread.php?120735-Cast-bullet-accuracy-and-trailing-edge-failure

Yeah boy...thanks R5R...you the man today!

That link just lead me to a 4 Volume set of books by F W Mann...'The Bullet's Flight' . . . "Whooopti Do!' . . . :bigsmyl2:

[runfiverun]

you'll love those books Charlie.

the original poster of that thread was a PHD type DR. of physics and mathematics
he unfortunately left us when someone here wouldn't get over some spin rate theory and nagged him to death about it.
which really sucks because he was working on some rotational stress numbers for me.

[OS OK]

Love those technical books...my wife just looks at me and shakes her head!

[Bama]

in muzzleloading round balls, we know that it is more important for the base to be perfect rather the nose.
I dont know why. But we know if the base is chewed up they wont group. But if the nose is chewed, it dont matter as much.
That is why we load with the sprue on top.
No doubt a similar thing exists with bullets.
I would imagine that a skewed base would have uneven gasses exiting the muzzle
When the bullet exits the barrel is what i was thinking. If one side exits even a small amount before the other the gasses will push the bullet to the opposite side and set up a large yaw. Even nicks in the edge should do the same thing just to a possible less degree. None of it is good for accuracy.

[OS OK]

There could be as much as 6,000 PSI exiting the muzzle right behind the boolit...that's quite a kick in the butt !

[popper]

Several years ago I purposely nicked the base of several 40SW and got a circular pattern on the target. Recently I shot some 145 gr PB in BO @ 2100 fps. Got the similar 'ring' on the target (100 yds, posted elsewhere). It's an AR so the port cut the base. Proof was a clogged gas key. Barrel has a good crown. GC jacket loads don't have the problem. My solution to not finding inexpensive nose pour moulds is a base that has a very short GC shank and bevels up to the drive band. Effectively the crown 'sees' a nice crisp beveled edge. It also seats straight quite easily. Works in 30/30 & 308 marlin run pretty hard. 308MX 1875 fps, 50 yds. 150gr PB WW + Cu.
207588

[Bama]

I am not sure what you mean by "reverse of crown" but bullits have bevel base, boat tail, and nose pour and adding a few wads to improve accuracy.

If a crown is dented or not cut square with the axis, it allow some of the gases to come out near the dent before the gas on the other side. Depending on the size and shape of the dent the high pressure gas will cause to bullet flight to be off from the bore axis. Recently had a barrel that when bore sighted, bullet would hit 8-10 ft to right of point of aim. Only thing we could find is crown was not cut square with bore axis. I have been applying gas checks using a homemade system which results in the slightly rounded corners of gas checks to be swagged to a very sharp 90 degree angle. I was wondering if this hurt or helped accuracy. I believe it helps.

[Larry Gibson]

you'll love those books Charlie.

the original poster of that thread was a PHD type DR. of physics and mathematics
he unfortunately left us when someone here wouldn't get over some spin rate theory and nagged him to death about it.
which really sucks because he was working on some rotational stress numbers for me.

The doctor, for all his self claimed ballistic knowledge, had very little understanding of ballistics not withstanding his pontifications of such knowledge. In the reference thread you listed in post #6 the doctor's lack of ballistic knowledge is self evident.

He begins with the title of his thread;

Cast bullet Accuracy and Trailing Edge Failure

The doctor then states;

"So I had a thought... Probably not a new one, but I haven't yet come across it exactly....... You would think since immediately prior to departure from the bore the base edge of a bullet is confining the gas pressure and restraining inertial wobble that a major impact to accuracy would be the beginning of blow out of this trailing edge due to gas pressure (+ other forces), and subsequent net off axis forces imparted to the bullet. Asymmetric venting during departure would impart forces, and further erosion/scarring could additionally influence the creation of net off-axis forces. Non uniform release of inertial forces could also tend to throw the shot."

Now with all the doctor's self claimed PHD ballistic knowledge you have to ask yourself.....why doesn't he already know the answer to his question? Could be he's asking a rhetorical question but the next two posts belie the truth;

When asked; “Have you ever heard of Dr. Mann's the flight of the bullet”

The doctor answer's with; "Was he the fellow who categorized types of imperfections vs. accuracy impact? Wrinkled, nose defects, base defects, etc? If so, I'm familiar with the experiment generalities but never came across the actual article....”

His own answer defines his own knowledge of ballistics. Anyone who has studied ballistics and claims to have a PHD in such studies is well aware of Dr. Mann's book and work. Obviously the doctor (DrB to be exact) was not as knowledgeable as he claimed. He was not "nagged" either. He was presented with facts concerning the adverse effect too much RPM can have on bullets and, not having the knowledge he claimed, could not refute those facts with ballistic evidence. Not sure why he left this forum but I'm sure being totally discredited by his own doing may have had something to do with it.

Now, if you would care to present actual ballistic evidence (facts) that discredits the "spin rate theory" we would all certainly like to see them? Probably a good thing never gave you the "rotational stress numbers" because they probably would have been wrong given his actual ballistic knowledge. The fact that he did not give you the numbers, after saying he would, probably speaks as well to his integrity.

BTW, another quote I like; "I don't have a PHD.....I have a DD 214......"

[Oklahoma Rebel]

sounds a bit judgemental to me, but I don't know the whole story....interesting stuff either way. I imagine the base of the boolit and the crown have equal consequences, but a marred or otherwise imperfect boolit base only lasts one shot, whereas a bad crown, well, can cause a major toothache!!!

[Larry Gibson]

....... I imagine the base of the boolit and the crown have equal consequences, but a marred or otherwise imperfect boolit base only lasts one shot, whereas a bad crown, well, can cause a major toothache!!!

Oklahoma Rebel

That certainly agrees with what I've found but some recent testing appears to demonstrate that a crown not square to the bore isn't as detrimental to accuracy as we think. It also agrees with most "experts" and ballisticians opinions. I've not done a test my self but know that I've corrected a lot of "accuracy" problems over the years with a simple recrowning of the muzzle. Perhaps there are more factors at play here than we think or are considering?

[vzerone]

sounds a bit judgemental to me, but I don't know the whole story....interesting stuff either way. I imagine the base of the boolit and the crown have equal consequences, but a marred or otherwise imperfect boolit base only lasts one shot, whereas a bad crown, well, can cause a major toothache!!!

I think that too Oklahoma Rebel. Far as I can see it looks like Larry Gibson has broken some forum rules. "Inflammatory Without Merit", "Insulting Other Member(s)" and "Condescending\Arrogant".

What are your credentials in external ballistics Larry? Don't tell me a DD 214 because that's not going to cut it. My God, Dr B has been gone long ago, and contrary to what you say you did nag him till he could no longer stand you and left, and yet you're still berating him and his education. I've spent hours and hours reading and going over all the old threads and nobody with credentials have agreed with you. Your theory isn't proven. I know from reading here other people have exceeded your threshold and then you came back said you can push it. Then why is it a threshold if you can push it? Definition of threshold:
the magnitude or intensity that must be exceeded for a certain reaction, phenomenon, result, or condition to occur or be manifested.
"nothing happens until the signal passes the threshold" Your threshold seems that you can maneuver it to be what you want it to be.

[MostlyLeverGuns]

This 'perfect crown' thing has been around a long time. Many experiments have shown that an imperfect crown has little to do with group size. Point of impact can be affected but group size has little change. If you burr or gouge the muzzle, a few shots might go wild due to burrs, but then groups will return. A worn muzzle due to improper cleaning, mostly old military rifles can affect grouping.
NOW perfect bullet bases are critical, back to Dr. Mann's experiments, the defective bullet base causes lots of trouble. How far you shoot comes into play. Crown angle, another boogey man, square, the magical 11 degrees, 45 degrees, 60 degrees, or rounded? IT really doesn't matter. The barrel Maker, Mr Obermeyer uses 60 degrees because that is what he has from the center used when turning or threading a barrel. He also cleans from the muzzle to reduce the possible damage to the throat, easier to shorten and remove muzzle damage than rethread and chamber. ALL these sacred cows, still alive from BEFORE the internet.

[Larry Gibson]

vzerone

Nothing condescending or inflammatory there in my post. I was responding to runfiverun's remark which some might consider "inflammatory". However, I do not consider his remark that but just his usual snide remarks. Other than that my remarks are facts based on what was said in the other thread.

The point is DrB claimed all sorts of "credentials in Ballistics" but it became quite apparent his knowledge on the topic was lacking. I do have a college degree but have learned far more from practical experience and learning by doing/experimenting than I did in college. What I did learn in the science classes I took was how to properly conduct an experiment with a sufficient sampling so that a correct conclusion may be reached. I know many highly educated people, including PHDs, who could not pour water out of a boot with out cutting the toe off to do it. Conversely I also know many highly educated people, including PHDs, who can and do use their education and knowledge correctly. I have been studying ballistics since I was in high school. I have continued through the years and have invested heavily in the study to be able to conduct and measure the results of tests/experiments. What I present is based on facts from that testing.

Did Dr. F. W. Mann have a PHD in Ballistics? No, he was a medical physician (general practitioner including obstetrics) With a degree in science. He began studying ballistics as a young man because he was intrigued by the bullets dispersion on target (what we call groups). He learned through tests and experimentation. We are fortunate for the results of his work.

When I first mentioned preliminary testing was indicating too much RPM might be the root cause of inaccuracy at high velocity on this forum long ago I was challenged by many on this forum. I was told by several "old sages" here that I must prove the theory. I went to great lengths of time and expense to prove the RPM Threshold was valid. Most knowledgeable shooters here believe that proof and believe the RPM Threshold is valid because they have experienced the effect of too much RPM resulting in loss of accuracy also.....at the RPM levels predicted. If you still doubt then you also are more than welcome to present actual test evidence proving otherwise. However, unless you actually post real test results with sufficient groups such as I have at 100, 200 and 300 yards then be prepared to have your results questioned. Posting what someone else says they have done, especially on the internet, without the actual test results is meaningless. Also posting cropped photos of a supposed 4 shot group at 312 yards by a relative is questionable.

You can indeed push up the RPM Threshold. I have also proven that not only on this forum but you can still find the information on the NOE Forum. However, even though you can push up the RPM Threshold you will still bump into it. Several claim by using Cu in the alloy and heat treating they attain "accuracy" at 2400 fps +/- from .308W ARs or similar rifles with 10" twists. For sake of argument let's just agree with that. So then if there is no RPM Threshold then why are they not pushing 2500 - 2600 fps from the .308W.....it certainly is capable. The RPM Threshold of 120,000 to 140,000 RPM is the "magnitude and intensity" based on the use of bullets cast of ternary alloys. Adding Cu, PPing, and it appears some PCing are some methods to push up the RPM Threshold.

However, all of this has nothing to do with the OP's question. I'm all for getting back on topic.

[oldblinddog]

I have done no testing on crowns that I puposely disfigured. However, I have recrowned more than one barrel with a hacksaw, square and file, and a 1" diameter grinder ball in a hand drill and obtained groups of less than one inch at 100 yards, so it can't be that hard. On the other hand, it has been my experience that the base of a cast bullet should be as near perfect as you can make it, even if you are covering it with a gas check.

[runfiverun]

sarcasm isn't snide.

[Shopdog]

Firearm-fixed(short term,throat brrl condition)

Target-fixed(stapled)

Shooting station-fixed

Skill-fixed(plateau)

'Bout the only thing not "fixed" is the bullet flight.So don't put fixed limits on a dynamic part of the equation.Just sayin.

[john.k]

I have recrowned barrels and counterbored worn muzzles,not due to any theory,but because owners paid to have it done.And I have read claims that a barrel crown needs to be accurate/even to within a millionth of an inch.Now if someone was willing to pay ,I could certainly charge extra for that.Whether it was achieved or not.But I have always theorized that if all this was so critical,why isnt porting of barrels ie Pendleton Dekicker /Swedish AG42....universally applied.Venting pressure from the exit discharge should work. IMHO,the shooters most likely to pay for anything that works would be the rimfire competition crowd.Do they?I dont know.Fixing their guns is like clockmaking,i cant do that either.

[Larry Gibson]

oldblinddog and john.k bring up some interesting points concerning just how "precise" does the crown have to be?

I have, many years ago, filed the bases of bullets so they were not square to the axis of the bullet. Accuracy with those was very poor.

I believe there was a test done with the results posted in CBA's "Fouling Shot". I'll try to find it.

[vzerone]

vzerone

Nothing condescending or inflammatory there in my post. I was responding to runfiverun's remark which some might consider "inflammatory". However, I do not consider his remark that but just his usual snide remarks. Other than that my remarks are facts based on what was said in the other thread.

The point is DrB claimed all sorts of "credentials in Ballistics" but it became quite apparent his knowledge on the topic was lacking. I do have a college degree but have learned far more from practical experience and learning by doing/experimenting than I did in college. What I did learn in the science classes I took was how to properly conduct an experiment with a sufficient sampling so that a correct conclusion may be reached. I know many highly educated people, including PHDs, who could not pour water out of a boot with out cutting the toe off to do it. Conversely I also know many highly educated people, including PHDs, who can and do use their education and knowledge correctly. I have been studying ballistics since I was in high school. I have continued through the years and have invested heavily in the study to be able to conduct and measure the results of tests/experiments. What I present is based on facts from that testing.

Did Dr. F. W. Mann have a PHD in Ballistics? No, he was a medical physician (general practitioner including obstetrics) With a degree in science. He began studying ballistics as a young man because he was intrigued by the bullets dispersion on target (what we call groups). He learned through tests and experimentation. We are fortunate for the results of his work.

When I first mentioned preliminary testing was indicating too much RPM might be the root cause of inaccuracy at high velocity on this forum long ago I was challenged by many on this forum. I was told by several "old sages" here that I must prove the theory. I went to great lengths of time and expense to prove the RPM Threshold was valid. Most knowledgeable shooters here believe that proof and believe the RPM Threshold is valid because they have experienced the effect of too much RPM resulting in loss of accuracy also.....at the RPM levels predicted. If you still doubt then you also are more than welcome to present actual test evidence proving otherwise. However, unless you actually post real test results with sufficient groups such as I have at 100, 200 and 300 yards then be prepared to have your results questioned. Posting what someone else says they have done, especially on the internet, without the actual test results is meaningless. Also posting cropped photos of a supposed 4 shot group at 312 yards by a relative is questionable.

You can indeed push up the RPM Threshold. I have also proven that not only on this forum but you can still find the information on the NOE Forum. However, even though you can push up the RPM Threshold you will still bump into it. Several claim by using Cu in the alloy and heat treating they attain "accuracy" at 2400 fps +/- from .308W ARs or similar rifles with 10" twists. For sake of argument let's just agree with that. So then if there is no RPM Threshold then why are they not pushing 2500 - 2600 fps from the .308W.....it certainly is capable. The RPM Threshold of 120,000 to 140,000 RPM is the "magnitude and intensity" based on the use of bullets cast of ternary alloys. Adding Cu, PPing, and it appears some PCing are some methods to push up the RPM Threshold.

However, all of this has nothing to do with the OP's question. I'm all for getting back on topic.

Well Larry those members shooting CU in the alloy aren't claims, they are facts. One member, who doesn't post much anymore, is getting full jacketed velocities with a 7mm-08. Now your mention of the AR10 with the ten twist reminds me of my cousin and you know who I'm talking about. I also wonder if you meant him, but he wasn't using CU in his alloy. Well he did 3100 fps with more then very good accuracy, but you and your minions just ran him into the ground. He done it, I've seen it, I've seen him do it again and again. Now he doesn't care about it. You've made this statement to a current member, which I won't mention, and he called it your "canned response" "about the small calibers not having enough distance away from the centerline of the bullet to be affected by the spin as much". With that said why did you fail the high velocity with accuracy test with the 6.5 Swede which can still be read here? Or did you purposely fail it to smite my cousin and another banned member? I'd say you just outright failed at it.

Larry you just can't or won't see that gripping the rifling and alloy flow under acceleration is the problem and that the spinning just exacerbates and magnifies those issues. You know about the famous seven twist Colt HBAR my cousin has. He has done some precise measurements of that barrel's bore and groove. Mainly the groove is of his concern. The dept of the rifling groove is barely .0025. That would give you a .006 across the grooves. He surmises that when you are going to manufacture a barrel that is going to be chromed in the bore and chamber that the manufacturer makes allowances for the chroming. Maybe Colt didn't??? Or maybe they didn't feel the smaller groove measurement was going to make any difference. Well it doesn't with jacketed, but it sure does with cast. You are correct about not getting accuracy with that seven twist HBAR, but not because of the rpm theory, but because of the reason stated at the beginning of this paragraph. What's even more amazing is that I've seen you mention shallow rifling is bad for cast in another post somewhere else or even some other forum. Yet you hold onto this rpm theory.

There are two current members, that I know of, at the present and closing in on 3000 fps velocity with reasonable accuracy using powder coat alloy bullets. So maybe Larry powder coat, paper patch, even unique alloy mixes are better gripped by shallow rifling. I know another thing that paper patch does for the alloy bullet and that is it keeps the heat from powder combustion and friction off it. Perhaps powder coat does the same, but unique alloys don't.

If rpm doesn't have a flaw to work on, it doesn't affect accuracy.

[vzerone]

BTW perfect crowns and perfect bullet bases are very old knowledge.

[swheeler]

:holysheep:killingpc

[Larry Gibson]

vzerone

If you read what you just posted (post #27) you validate the RPM Threshold and explain why it exists.

I know a bullet with Cu in it can push the RPM Threshold.....I said that not only in this thread but in numerous other threads. I have tested bullets with Cu in it, one of those "former" members you mention sent me the babbitt and useful information. I also have tested PC'd bullets and have pushed the RPM threshold with them. I've posted the results of both on this forum. Even so, the RPM threshold is only pushed up....it is still there with those bullets. Obviously you have problems understanding the RPM Threshold of 120,000 - 140,000 RPM applies to ternary alloyed bullets not those with Cu in them or those that are PC'd.

I have no idea what you mean by "canned response" but the higher the rotational velocity the greater the adverse affect of any defect will be given the same RPM.

"If rpm doesn't have a flaw to work on, it doesn't affect accuracy."

Absolutely correct. By posting such you obviously admit to the adverse affect RPM has on accuracy. Thank you for finally coming to the correct conclusion.

I'll not enter into a discussion of your cousins, shall we say, bodacious claims as they've been discussed too many times before. The completeness of my testing on the 6.5 Swede thread speaks for itself. No one else posted any factual test evidence of doing any better.

As to closing in on 3000 fps......I closed in on it last year using a ternary alloy (#2 alloy) cast bullet (the 30 XCB) and held 1 1/2 moa accuracy with 10 shot groups at 100, 200 and 300 yards consistently.

[Shopdog]

"One hit wonders".... sheesh.

I'll never forget gettin front page coverage on/in Southern Living mag.....

[Larry Gibson]

sarcasm isn't snide.

Before admitting to using something you might want to look up its meaning. I was being nice and continuing to give you the benefit of the doubt using the term "snide".

According to Webster's New Collegiate Dictionary "sarcasm" is defined as; 1. a sharp and often satirical or ironic utterance designed to cut or give pain. 2. a mode of satirical wit depending for its effect on bitter, caustic, and often ironic language that is usually directed against an individual.

Thus your "sarcasm" is duly noted.

Now, can you and vzerone kindly knock off what has been hashed out so many times and just let this thread get back on topic? I for one would appreciate it as I'm sure would most everyone else.

[vzerone]

vzerone

If you read what you just posted (post #27) you validate the RPM Threshold and explain why it exists.

I know a bullet with Cu in it can push the RPM Threshold.....I said that not only in this thread but in numerous other threads. I have tested bullets with Cu in it, one of those "former" members you mention sent me the babbitt and useful information. I also have tested PC'd bullets and have pushed the RPM threshold with them. I've posted the results of both on this forum. Even so, the RPM threshold is only pushed up....it is still there with those bullets. Obviously you have problems understanding the RPM Threshold of 120,000 - 140,000 RPM applies to ternary alloyed bullets not those with Cu in them or those that are PC'd.

I have no idea what you mean by "canned response" but the higher the rotational velocity the greater the adverse affect of any defect will be given the same RPM.

"If rpm doesn't have a flaw to work on, it doesn't affect accuracy."

Absolutely correct. By posting such you obviously admit to the adverse affect RPM has on accuracy. Thank you for finally coming to the correct conclusion.

I'll not enter into a discussion of your cousins, shall we say, bodacious claims as they've been discussed too many times before. The completeness of my testing on the 6.5 Swede thread speaks for itself. No one else posted any factual test evidence of doing any better.

As to closing in on 3000 fps......I closed in on it last year using a ternary alloy (#2 alloy) cast bullet (the 30 XCB) and held 1 1/2 moa accuracy with 10 shot groups at 100, 200 and 300 yards consistently.

No Larry I don't admit to your false theory. Anyone that casts good bullets, loads them properly, good lube, and the bullets start straight there is no rpm theory.

You know I see you're nit picking on Runfiverun, so legal season then. As I mentioned your "minions" I see one showed up and put up some emoticons. I leave you with this

Knowing the truth, seeing the evidence of the truth, but still believing the lie.

I'll use your ploy, let's get back to the original posters questions.

[blackthorn]

Here we go again with the "this guy I know" or "my cousin did this" but never any documentation to back it up. This kind of garbage cost us more than one top notch contributor to this forum in the past! Hey Larry, for what its worth---it never pays to interact with trolls! It's sort of like trying to teach a pig to sing---frustrates you and aggravates the pig!

[OS OK]

Here we go again with the "this guy I know" or "my cousin did this" but never any documentation to back it up. This kind of garbage cost us more than one top notch contributor to this forum in the past! Hey Larry, for what its worth---it never pays to interact with trolls! It's sort of like trying to teach a pig to sing---frustrates you and aggravates the pig!

Nailed it...you must be a framer! . . . :bigsmyl2:

Especially about loosing the top notch contributors, their hard to come by...Ever now and then a post like this one will get deep and danged interesting but there's always someone and his kinfolk to contend with.

I wish some of you 'drive by commenters' would put the effort into a quality thread, jam packed with facts and pictures ever now and then...it'd make the arguments a lot more tolerable.

[JBinMN]

I am not sure I understand what some folks are saying for sure in the last 10 or so posts about other topics, but due to my own previous experience in another field, I do know that items in rotation, do show an effect of more deviation of path due to defects/changes in rotation.( in my case/experience by "doing" & "testing", aviation & "tracking" "helo" blades & propellers in particular)

Thus, I can visualize/understand how the path of a bullet that has a certain defect would not follow the same path as others without the same defect, or others that had dissimilar defect(s) would not follow the same path as the former, nor the same as bullets without defect.

How I see this in my head is... A set of blades/props that has one that has a defect, or is out of adjustment(OOA), can have an effect on the others, even though the others may have no defect/OOA situation, due to the same rotational path of the set. The speed is the same, the torque is the same, every thing is the same but the defect(s).
[Or, perhaps dissimilar materials used in manufacture. I.E. - Fiberglass &/or metal construction, wood, different assembly components et al, etc.]

In aviation,( or used to do it) we test for such situations so that we can try to find the optimal set of parameters that makes each work as a whole & not as an individual.

To me, it is the same with bullets/boolits/projectiles of any kind. Could be a rock, or a missile. If they are not the same as each other, they will react differently due to any factor that may have influence.

Be it "rotation" differences in lands & grooves, or differences in the powder charge or prime or combination, crimp, or lack of, etc... they are all factors to be considered.

In the case(s) of my experiences testing & correcting blade tracking issues( in particular), I have found that even when all components are the same type & manufacturer, there may still be cases of one having a defect or being just different enough, but still in specifications from the others, that an OOA condition can be noticed as compared from the others rotational path & correction needs to be made for optimal & efficient performance.
http://aviationmaintenance.tpub.com/TM-1-1500-204-23-5/css/TM-1-1500-204-23-5_68.htm


I see no difference in bullets or boolits...

Any differences of opinion about one of the "factors" such as RPMS,etc. is likely a different topic subject than the OP here. ( & seems to be, from some time before)

To "try" to paraphrase the OP & what I got from it's intentions...

"What effect does a bullet/boolits shape at the "Trailing edge" have on its' accuracy as far as being different from a normal one?

Or something along those lines...

I said before I think it does have an effect & it appears so do more than a few here & other places...

Are we back to the regular scheduled program?
;)

[john.k]

I have no doubt that all of the research into this was done over 100 years ago,in respect to artillery projectiles.The results are probably still top secret,buried in the archives .Factors relating to the barrel are easily controlled, but once the projectile is free of the barrel,then how many variables are there?I dont know,and its certainly beyond the means of any private person to investigate in a scientific manner.......Here s one more variable...I recently fired and recovered some cast bullets,and i have noted that paper patched flat based bullets develop a small uneven bevel around the base when fired.But imagine how much Dr Mann could have achieved with a labradar and high speed video recording.Look in the archives,dont ask to reinvent the wheel.

[Shopdog]

Let me get this straight.... if I rip off someone else's work,change a "name" and present it as fact,that anybody questioning it is somehow not paying due diligence?

[Larry Gibson]

For those CBA members the Fouling Shot article is "The Need for a Perfect Crown is a Myth" - John Alexander, Fouling Shot Jul-Aug 2014. I'll have to check and see if I can repost it here.

[Bama]

Hey Guys, I didn't mean to stirr up such an issue. I was trying to get some insight into something I thought I was seeing. I put my gas checks on with a small mallet and a fitted nose punch. I reamed a piece of shafting the same size as an "as cast boolit". A short section the height of a gas check is reamed to diameter of gas checkon one end. in operation the gas check is pushed into bottom, boolit dropped through top and nose punch slid in from top. The rawhide mallet is used to fully seat and expand the boolit base into gas check. This in line application insures the gas check is almost perfectly square with the base of boolit. Crimping the check is carried out with push through seater in a separate operation. This is where the deviation was observed. When lightly tapped into place the gas checks still had the slightly rounded corners at the sides of base (nornady checks). If not done lightly (strong taps) the bottom corners were sharp 90 degrees when pushed through the sizing dies. I have not tried to do a full scale test to determine the best accuracy to date but the 90 degree bases "seems" to be more consistent. Just wondering if there was a scientific basics for one to be more accurate than the other.