Cannelures

Bucksnort1 · January 19, 2016, 08:28 PM

Last week, a friend was with me when I loaded some 44 magnum JHPs with cannelures. He is not a re-loader. I explained a few things to him including why we sometimes seat bullets with cannelures to the cannelure then crimp at that point. He asked if there is any leakage of gasses at the cannelure. That is my question.

Is there any gas leakage at the cannelure?

Ole Joe Clark · January 19, 2016, 09:04 PM

No

Bucksnort1 · January 20, 2016, 09:52 AM

Ole Joe,

You are a man of few words. Thanks.

F. Guffey · January 20, 2016, 10:01 AM

Quote:

Is there any gas leakage at the cannelure?

I suggest reloaders purchase R. Lee’s book on modern reloading; and then read it. I know there are many reloaders that claim they purchased the book; base on feed back I see little evidence their book has ever been opened, just saying.

Older reloading manuals suggested crimping was a bad habit because their was an illusion crimping improved bullet hole. Granted; that created an answer without a question; meaning before the Internet there was bullet hold, after the Internet someone invented neck tension with no way to measure it. I have tension gages, all of my tension gages measure in pounds not tensions. I have deviation gages, my deviations gages measure in pounds of deflection; the gages that are not calibrated in pounds or marked off in thousandths.

If the bullet has a cannelure and a crimp is to be applied it is suggested the crimp be applied at the cannuler. Then there is that thing about following instructions and the cannelure is not located where the reloader thinks it should ‘be located’.

I have a machine, the machine allows me to add a cannelure or it allows me to apply a cannelure on a bullet that did not have one. My opinion; the tool is nothing more than something nice to have because I do not have a tool that measure neck tension. I have tools that measure bullet hold. I want all the bullet hold I can get.

Quote:

I explained a few things to him including why we sometimes seat bullets with cannelures to the cannelure then crimp at that point.

http://m14forum.com/ammunition/79474...cannelure.html

F. Guffey · January 20, 2016, 10:40 AM

Quote:

No

Quote:

You are a man of few words. Thanks.

If there is leakage the leakage is around the bullet. For years reloaders thought the bullet was ‘THE SEAL’. And then? Before that the military had to change everything they thought they knew about the sequence of events beginning with dropping the firing pin on the primer.

A photographer decided he would stand behind a big gun to catch the moment the crew lit up the sky. When he developed the photograph he had no ideal what he was looking at. Not knowing what he was looking at did not slow him down. He published the picture and won and the picture was recognized as ‘art’.

Later the military saw the picture and said something like “WHAT!?” It tool the military types months to sort things out. The biggy was gas passing the bullet.

F. Guffey

Forgive, all of this took place +/- a few years of 1913.

Mauser69 · January 20, 2016, 10:40 AM

Quote:

I suggest reloaders purchase R. Lee’s book on modern reloading; and then read it. I know there are many reloaders that claim they purchased the book; base on feed back I see little evidence their book has ever been opened, just saying.

Man, ain't that the truth!

**Unclenick** · January 20, 2016, 10:21 PM

Mr. Guffey is giving both excellent advice and a good example of gas bypass.

If you look online for some of the super high speed slow motion video of bullets firing, you see the puff of bypass gas that precedes the bullet to the muzzle. Dr. Lloyd Brownell describes how it is affected by seating depth and how it, in turn, affects peak pressure. Look at pages 45-51, here.

The main thing is that pressure expands the brass at the neck away from the bullet faster than it can move the bullet mass significantly forward. Therefore, gas starts leaking out at the case mouth and goes around the bullet until the bullet covers the free-travel distance (aka, bullet jump to the lands) so its widest diameter can begin creating a seal. That's the gas you see preceding the bullet in the slow motion videos.

Pressure peels the neck brass from the bullet starting at the bullet base and moving forward. At the moment the lifting of the brass reaches the case mouth, gas starts to escape, creating a pressure drop that stops the neck being expanded much further. The result, which you can find on any rifle case, is the mouth of the case hasn't expanded quite as much as the rest of the neck below it. Often, if the chamber neck isn't too loose, you find a new bullet will not fall into it until you expand it slightly.

Below is an image of .308 case, the bottom one a newly fired case and the upper one well-used. Both show the little bit of inward curl at the mouth.

So How does a cannelure affect that? My expectation would be that when there is a crimped cannelure, it will delay the start of bypass because the crimped case mouth takes a little more time and effort to lift clear of the bullet, which is probably how it raises start pressure. It would seem likely that as it starts to lift, gas can, indeed, start to bleed through the grooves in the cannelure, so the mouth may not lift quite as far as it does from a smooth bullet surface until after the bullet had moved the cannelure past the mouth, and thus it adds a little drag to the bullet's initial motion. A cast bullet crimp groove would behave no differently. Indeed, I have some jacketed bullets of foreign manufacture that have crimp grooves in them; a sort of toothless cannelure. They are not very accurate, though. It's not easy to avoid distorting a bullet when you roll any kind of groove into it. This is why match bullets don't have cannelures. Though, frankly, the big bullet makers have gotten pretty good at rolling cannelures with minimal distortion, and I've had some very accurate Hornady and Sierra bullets that have cannelures.

buck460XVR · January 21, 2016, 02:04 PM

IMHO, the cannelure is so short, relative to the rest of the seated bullet, that gas leaking past it, would have already passed by the rest of the seated bullet. Thus, no different than an uncannelured bullet using a taper crimp. Now if the cannelure ran the whole length of the seated part of the bullet, you might have an issue.

Ole Joe Clark · January 22, 2016, 08:26 PM

The OP asked the question: Does gas leak at the channelure? Not the base. As the bullet exits the barrel gas will mushroom out of the barrel and past the base of the bullet. The short answer to the question is still "No."

flashhole · January 22, 2016, 08:36 PM

What would the perfect round with a crimp look like?

Consider putting the loaded round under a microscope. What would you expect to see?

If you had to make thousands of loaded rounds with "acceptable" performance, what engineering design tradeoffs would you make?

F. Guffey · January 25, 2016, 10:16 AM

Quote:

The OP asked the question: Does gas leak at the channelure? Not the base. As the bullet exits the barrel gas will mushroom out of the barrel and past the base of the bullet. The short answer to the question is still "No."

I understood the question; it reminds me of the topic of annealing when reloaders start telling me everything they know about the subject of annealing. Gas passes the bullet, again, I believe a good start for a reloader would be to purchase R. Lee’s book on modern reloading. Next? Read the book.

Then there was this picture taken the moment the bullet left the barrel close to 100 years ago. The picture never made it to a reloading manual it did however make to a book or art; anyhow, that is where I found it. There it is, the atmosphere so compressed moisture is visible in the form of a cloud. And then; the smoke ring, behind the smoke ring the bullet, behind the bullet the rest of the gas so defined the rifling can be counted. The rest of the gas left the barrel at 90 degree.

F. Guffey

January 19, 2016, 08:28 PM	#1
Bucksnort1 Senior Member Join Date: July 8, 2013 Location: Littleton, Colorado Posts: 1,121	Cannelures Last week, a friend was with me when I loaded some 44 magnum JHPs with cannelures. He is not a re-loader. I explained a few things to him including why we sometimes seat bullets with cannelures to the cannelure then crimp at that point. He asked if there is any leakage of gasses at the cannelure. That is my question. Is there any gas leakage at the cannelure?

January 20, 2016, 10:21 PM	#7
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Mr. Guffey is giving both excellent advice and a good example of gas bypass. If you look online for some of the super high speed slow motion video of bullets firing, you see the puff of bypass gas that precedes the bullet to the muzzle. Dr. Lloyd Brownell describes how it is affected by seating depth and how it, in turn, affects peak pressure. Look at pages 45-51, here. The main thing is that pressure expands the brass at the neck away from the bullet faster than it can move the bullet mass significantly forward. Therefore, gas starts leaking out at the case mouth and goes around the bullet until the bullet covers the free-travel distance (aka, bullet jump to the lands) so its widest diameter can begin creating a seal. That's the gas you see preceding the bullet in the slow motion videos. Pressure peels the neck brass from the bullet starting at the bullet base and moving forward. At the moment the lifting of the brass reaches the case mouth, gas starts to escape, creating a pressure drop that stops the neck being expanded much further. The result, which you can find on any rifle case, is the mouth of the case hasn't expanded quite as much as the rest of the neck below it. Often, if the chamber neck isn't too loose, you find a new bullet will not fall into it until you expand it slightly. Below is an image of .308 case, the bottom one a newly fired case and the upper one well-used. Both show the little bit of inward curl at the mouth. So How does a cannelure affect that? My expectation would be that when there is a crimped cannelure, it will delay the start of bypass because the crimped case mouth takes a little more time and effort to lift clear of the bullet, which is probably how it raises start pressure. It would seem likely that as it starts to lift, gas can, indeed, start to bleed through the grooves in the cannelure, so the mouth may not lift quite as far as it does from a smooth bullet surface until after the bullet had moved the cannelure past the mouth, and thus it adds a little drag to the bullet's initial motion. A cast bullet crimp groove would behave no differently. Indeed, I have some jacketed bullets of foreign manufacture that have crimp grooves in them; a sort of toothless cannelure. They are not very accurate, though. It's not easy to avoid distorting a bullet when you roll any kind of groove into it. This is why match bullets don't have cannelures. Though, frankly, the big bullet makers have gotten pretty good at rolling cannelures with minimal distortion, and I've had some very accurate Hornady and Sierra bullets that have cannelures. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

January 22, 2016, 08:36 PM	#10
flashhole Senior Member Join Date: February 9, 2005 Location: Owego, NY Posts: 2,000	What would the perfect round with a crimp look like? Consider putting the loaded round under a microscope. What would you expect to see? If you had to make thousands of loaded rounds with "acceptable" performance, what engineering design tradeoffs would you make? __________________ ,,, stupidity comes to some people very easily. 8/22/2017 my wife in a discussion about Liberals. Are you ready for civil war?

January 19, 2016, 09:04 PM	#2
Ole Joe Clark Member Join Date: March 14, 2015 Location: Heart of Dixie Posts: 52	No

January 20, 2016, 09:52 AM	#3
Bucksnort1 Senior Member Join Date: July 8, 2013 Location: Littleton, Colorado Posts: 1,121	Ole Joe, You are a man of few words. Thanks.

January 21, 2016, 02:04 PM	#8
buck460XVR Senior Member Join Date: December 28, 2006 Posts: 4,342	IMHO, the cannelure is so short, relative to the rest of the seated bullet, that gas leaking past it, would have already passed by the rest of the seated bullet. Thus, no different than an uncannelured bullet using a taper crimp. Now if the cannelure ran the whole length of the seated part of the bullet, you might have an issue.

January 22, 2016, 08:26 PM	#9
Ole Joe Clark Member Join Date: March 14, 2015 Location: Heart of Dixie Posts: 52	The OP asked the question: Does gas leak at the channelure? Not the base. As the bullet exits the barrel gas will mushroom out of the barrel and past the base of the bullet. The short answer to the question is still "No."