cannelure placement

[Kevatc]

Both are 55 gr FMJBT's. The one on the left is a Montana Gold the one on the right is a Hornady. Why isn't the placement of the cannelure standard?

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[deadshot2]

In the end, it only matters if one's crimping. I find the Montana Gold to be just right when cases are trimmed to 1.750 and OAL is 2.255" The military tech manual indicates that the cannelure should be about .510 from the meplat of the bullet when working backwards off their drawings for M-193 round.

 

[Kevatc]

In the end, it only matters if one's crimping. I find the Montana Gold to be just right when cases are trimmed to 1.750 and OAL is 2.255" The military tech manual indicates that the cannelure should be about .510 from the meplat of the bullet when working backwards off their drawings for M-193 round.

I crimp so I am going to have to do some die adjustments. Still, why isn't the cannelure standardized????

 

[ma96782]

I crimp so I am going to have to do some die adjustments. Still, why isn't the cannelure standardized????

I suspect that the various mfns use the spec that they want.

That being said............

If I were the mfn and assuming that I'd want the bullet to be crimped in it's provided cannelure. I'd put the cannelure where the OAL of the finished round, will meet my spec for OAL (keeping in mind the internal magazine length spec).

You'd usually see that most "standard" bullet weights used with popular weapons, will have the cannelure placed in about the same place. But, because of various construction materials and shapes that are/can be used when making bullets, the cannelure placement can vary from slight to alot.

Aloha, Mark

PS..........try this..........

Using the two different bullets (say X and Y brand) try crimping them in the cannelure and measure the OAL. Also, try loading them into a magazine. IF X brand of bullet won't fit into a magazine then, I guess I won't be buying any more of that stuff. OR, I could just forget about the cannelure and go from there.

 

[nrc]

The ogive on those two are different.

If you are one of those fellows who is chasing accuracy - It's not how close the 'point' is to the rifling, its at what point does the bullet at its apex contact the rifling. If you crimp both of those in their respective cannelures, you will engage the rifling at about* the same time. I say about* because they are made by entirely different companies on different assembly lines...

If you are banging away at soda cans (quite fun in its own right) then it doesn't make enough difference to matter.

 

[Kevatc]

OR, I could just forget about the cannelure and go from there.

Wouldn't I see different pressures if I don't worry about the cannelure? Perhaps the slight difference in cannelure and seating depth might not make much of a difference?????

 

[Spitpatch]

Reading perhaps more into your question than what is actually there, I truly think the answer to your question is that if you change bullets, you definitely need to change a lot of other things (or at least examine them). Your good scrutinization of components (and resulting discovery of differing cannelure placement) is a healthy trait to continue to cultivate. nrc is absolutely right with his drawing of attention to the ogive.

With a good safe load with the bullet that seats more shallow, no horrible problem may erupt if you willy-nilly switch to the bullet that seats deeper, but pressures may indeed change, point of impact may indeed change, group size may indeed change, etc., etc., etc. The axiom here is that changing bullets requires that you begin again with load development for the new bullet (and that would include adjusting of the equipment, including seating depth). This "back to the drawing board" rule is not only beneficial from a safety standpoint, but also conducive to accuracy pursuits.

You will also find manufaturer-to-manufacturer inconsistencies with primers (one may seat more firmly than another, etc.), brass (capacity, rim thickness,etc.). We cannot just go "mixing and matching" to our heart's content if we want the best ammunition from our little factories at home.

Finally, I will restate my practice of not bothering with crimps and cannelures and such with my AR. Nor would I oppose the practice for those that choose it. I have simply found it not necessary for my purposes: my gun is a sporting weapon, not a battle gun. I have tried every way I can think of to make my bullets "walk" out of (or into) the case neck, and short of putting the cartridge in the Quinetic, it just doesn't happen. My crimping activities therefore remain restricted to revolver loads, and my blackpowder cartridge guns. For those operations, I share with others a devotion and trust for the consistency offered by Lee's "factory crimp" dies. Probably the best product Lee has ever developed.

Abandoning any thought of crimping AR cartridges allows for an almost infinitely vast selection of "cannelure-less" sleek-sided bullets to choose from, and allows me to choose seating depth without the dictation of crimping concerns. My criteria become magazine operation and throat placement.

 

[Kevatc]

Reading perhaps more into your question than what is actually there, I truly think the answer to your question is that if you change bullets, you definitely need to change a lot of other things (or at least examine them). Your good scrutinization of components (and resulting discovery of differing cannelure placement) is a healthy trait to continue to cultivate. nrc is absolutely right with his drawing of attention to the ogive.

With a good safe load with the bullet that seats more shallow, no horrible problem may erupt if you willy-nilly switch to the bullet that seats deeper, but pressures may indeed change, point of impact may indeed change, group size may indeed change, etc., etc., etc. The axiom here is that changing bullets requires that you begin again with load development for the new bullet (and that would include adjusting of the equipment, including seating depth). This "back to the drawing board" rule is not only beneficial from a safety standpoint, but also conducive to accuracy pursuits.

You will also find manufaturer-to-manufacturer inconsistencies with primers (one may seat more firmly than another, etc.), brass (capacity, rim thickness,etc.). We cannot just go "mixing and matching" to our heart's content if we want the best ammunition from our little factories at home.

Finally, I will restate my practice of not bothering with crimps and cannelures and such with my AR. Nor would I oppose the practice for those that choose it. I have simply found it not necessary for my purposes: my gun is a sporting weapon, not a battle gun. I have tried every way I can think of to make my bullets "walk" out of (or into) the case neck, and short of putting the cartridge in the Quinetic, it just doesn't happen. My crimping activities therefore remain restricted to revolver loads, and my blackpowder cartridge guns. For those operations, I share with others a devotion and trust for the consistency offered by Lee's "factory crimp" dies. Probably the best product Lee has ever developed.

Abandoning any thought of crimping AR cartridges allows for an almost infinitely vast selection of "cannelure-less" sleek-sided bullets to choose from, and allows me to choose seating depth without the dictation of crimping concerns. My criteria become magazine operation and throat placement.

Good post. Thanks for your thoughts.

 

[IheartGUNS]

I don't know why but I started to laugh when I read the heading and saw the picture. Why in the heck would the cannelure be in different places? At first I was going to respond, but after looking at the picture I'm a bit confused myself...

 

[Spitpatch]

Once again, nrc's post is a concise explanation: The point at wich the bullet ACTUALLY BECOMES .224 diameter (as you examine it from top to bottom) is the same (or nearly the same) distance from the cannelure, which would make the bullet rest in the chamber at the same (or nearly the same) distance from engaging the rifling. The two bullets differ in taper, and therefore differ in cannelure placement.

 

[deadshot2]

The two bullets differ in taper, and therefore differ in cannelure placement.

This still begs the question of why they aren't "standard" for placement above the base. If you crimp each of these bullets in the cannelure like tradition calls for, you'll end up with two widely different OAL's and/or bullet insertion depths. All this for the same bullet weight and intended use.

Yes, the cannelure can contribute to drag but the military still wants it because on the lighter bullets (55 gr. and 62 gr.) it increases the bullets tendency to fragment or break apart at the cannelure. They even forced the almighty Sierra to add a cannelure to their bullets even though Sierra said it wasn't necessary for the MK282 ammo.

Reminds me of something my Dad always told me. "Reason? There doesn't have to be a reason. That's just the way it is."

 

[Spitpatch]

I would agree, that for someone who would change bullets (all but weight and "purpose"), the resulting overall length and seating depth may well cause some difficulty if that person expected everything to be the same with such a bullet change. In fact, I shared this concern when viewing these two bullets, wondering if the one of "shorter" cannelure distance from the base might result (if seated/crimped properly) in an OAL not compatible with an AR magazine. One more reason I enjoy my exemption from crimping concerns.

However, if we keep in mind that changing a component (especially bullets) may well change ALL ELSE in the loading procedure and/or usage, such "difficulty" is predictable and usually easily dealt with.

The fact that two bullets are the same weight and "purpose" does not exempt the handloader from accomodation to the changed component. Stepping away from the example at hand, there exists a plethora of .308 150g weight bullets with the "purpose" of killing deer. There even exists more than one style of 150g deer bullet from each of many manufacturers. If I load my .30-06 with one 150g deer bullet, and then switch to a different 150g deer bullet (even from the SAME manufacturer), I can well expect to make more than one adjustment in my loading procedure for the new bullet.

(Dad was right. That's just the way it is.)

 

[ma96782]

YES, bullet seating depth will affect pressures. And, I'm not just talking about waaay deep or waaay out seating. Just a little bit can and will make a difference. But, at what point are you at that unsafe level?

Besides..........do you have the equipment to test?

And YES there are many other factors that also affect pressure. From your choice in primers, powder, brass, etc.....


Check this out: http://www.frfrogspad.com/miscelld.htm#components

and this warning from Speer Bullets........

IMPORTANT NOTE: Reloading data published by SPEER are for SPEER bullets. Many of our bullets are of unique construction; there is no such thing as "generic loading data" any more. Other bullet makes may produce significantly different pressures and velocities. We make no warranty that our published loads are safe with another make of bullet. You, the reloader, bear the ultimate responsibility for knowing your firearm, loading equipment, and techniques.

But with that being said..........many reloaders will experiment so.......

A prudent reloader doesn't try for max pressure or velocity out of their first try. Most prudent reloaders will, "work up their loads." They will READ their brass for possible signs of over pressure. And, even that isn't without pitfalls.

So, SOP is to "work up a load".........while watching/reading/looking.

Most reloading manuals/books will have this warning………

WARNING: Because of variations in powders from lot to lot, and variations and differences in components, the handloader should use the data in this manual as a guide. Do not start with the heaviest load shown. Start low, and try successively heavier charges carefully, watching for signs of excessive pressure, before increasing the charge. Many individual guns will safely handle greater charges of powder than shown here, but don't start at the top. Another reason for caution is that loads safe at normal temperatures can have excessive pressure if shot in either very hot or very cold temperatures.

I'd suspect that most reloaders are looking for accuracy (besides saving money). You can measure that. But, pressure is a lot harder to measure. So even when you're using reliable data, you should still be "working up your loads."

Aloha, Mark

 

[ma96782]

When I said.

OR, I could just forget about the cannelure and go from there.

I was talking about..............

Who says that I HAVE TO seat my bullet exactly where the cannelure is placed?

I could/can just seat the bullet where I wanted (within reason). And, I didn't mention "working up loads" (at that time) because that is SOP with prudent reloaders.

Aloha, Mark

 

[motoman98]

I don't use the cannelure for locating my bullet seating depth, either. Working back from the start of the rifling I allow a proper clearance and TAPER CRIMP for those rifles that reccomend a crimp. Much less trouble!

 

[deadshot2]

. But, pressure is a lot harder to measure.

Actually it's a lot easier than it used to be. For just a little more than the price of a good hunting rifle one can buy a Pressure Trace system which includes a CED Chronograph and analytical software. You can add strain gauges to each of your rifles if you want for only a small cost. It's the RSI Pressure Trace system. Considering what we spend on the rest of our equipment and rifles it's not that bad. Many of the Long Range Shooters (1,000 yard and up) are using this system because they are going to set their own standards for loads, not pull them out of some book.