Cartridge neck length vs throat erosion

[TAJ45]

Heard/read this mentioned when someone recommended the 6mm Rem AI'd over the .243 AI. The 6 Rem was said to have less erosion b/c of the longer neck.......fact?

I had not heard this stated before and am curious if this is factual or more opinion/personal perception than reality. Thought I'd toss it out here to try and see what shakes out.

 

[Dgd6mm]

Nobody, Anybody? I'm curious also. ;D

 

[357Mag]

Taj -

Howdy !

In general ( not specific to one cartridge )....

If the case's " turbulence point " is inside the neck, then throat errosion is better held in-check; than when the turbulence point lies outside the neck.... inside the barrel itself.

In side view, trace two lines depiciting the shoulder angle of the case in question, and see where the lines intersect. If shown to intersect inside the case' neck, throat errosion should eb minimized.

With regards,

357Mag

 

[fdshuster]

TAJ45:I put this thought up for consideration, on this site several years ago & was quickly shot down for suggesting it.

I was made aware of a study done by Speedy Gonzales that included diagrams showing the path of the unburned granuals or whatever comes out the mouth of the case, and his drawings show the granuals following the inside of the case shoulder, then "bending" and blowing straight out the neck, because of the force of the blast. His theory is that the granuals cannot continue to follow the straight line of the shoulder because of the force of the blast.

If you make a sketch it's easier to visualize the theory. Seemed to be one of the reasons for the throat erosion of a 243 with the 20 degree shoulder angle, compared to the 30 degree's of a 6BR, for example.

It seemed like a valid point & I have never voiced an opinion, either pro or con, since then.

 

[Leonardo63]

If using the theory of the convergence of fire based on the shoulder angle then all the AI designs would put that point within the neck regardless of neck length I'm pretty sure.
Recently I saw what sounded most probable. Flame cutting from blowing by the bullet before it was fully engaged in the rifling to create a seal. Supposedly, longer bullets that were deep seated in long necks, while into the lands, allowed the bullet to seal in the bore before the base left the case mouth.
Seems to make sense. So, this may lend to longer necks somewhat?, but would rely primarily on length of the bullets full diameter.
But bottom line, I think it comes down to big powder and high heat and shooting it up hotter and hotter.
Just ideas and postings I've read on here by much more experienced than I.

 

[fdshuster]

Leonardo63: And Ackley Improved's are not known for their longer barrel life, compared to the parent case/ cartridge. I lean toward believing it's nothing more complicated than amount of powder versus diameter of bore, but won't argue either way. Way above my pay grade.

 

[Leonardo63]

I agree FD- And I have one of those Ai in 22-250. Was going to do a 243AI until a guy talked me out of it purely on barrel life. He said the 243 was really bad and going improved was even worse. Again, from a guy much wiser than I

 

[Steve Blair]

So if the throat is the most susceptible portion of the bore for erosion to take place, why do we not experience erosion of the cartridge case necks? Figure that one out you big brain gun guys.

[br]
Copper alloys have higher melting points, do not burn like steel does and have excellent thermal conductivity, moving heat away from the neck rapidly. [br]
I never had a 6mm AI but have three 6mm Remingtons and owned another. None are good on barrel life. If you burn up to 50 grains of powder in a 6mm bore at full pressure, the result is predictable. [br]
The longer neck does give you more flexibility in bullet seating. The 6mm Rem and AI have ~.350" necks. That may be more than they need but allows shooting a wide range of bullets without hitting the neck-shoulder junction.

 

[robbor]

For what its worth here is an article.
http://www.reloadersnest.com/article_shoulder_angle_oct2603.asp

 

[fdshuster]

robbor: Excellent, thanks for posting.

"Short necks also cause more throat erosion than those cartridges with longer necks", really got my attention as I'm having an issue with a 6 BRX chambering ( short neck) compared to numerous 6BR chamberings, (longer case neck).

Watching it progress with my borescope and the BRX is "doing it" at a much faster rate than the 6BR's.Has to be a good comparison. Same shoulder angle, case design except for the neck length difference, and only 2 1/2 to 3 grains more of the same powder.

 

[TAJ45]

Thank you all for your thoughts and referenced article. I wuz kinda wondering if I had hit a previously mentioned topic that somehow went, let's say, less than "good" - when I didn't have a response after a reasonable time.

I'm kinda kicking around a "new improved" wildcat........yah, you all can get up off the floor when you're through laughing............and having read the neck length thing, wondered if I should include that feature in my "Same Hole" wildcat.

I think most shooters secretly want to design something different at least one time before they rack the rifle for the last time.

Again, thanks.

Tom
NRA Life ' 76

 

[Hombre0321]

Don't really know if this short throat, short barrel life holds up. Their is an extreme example of this being done and I do mean extreme. Stan Wares Wolf Pup cartridge has an extremely short neck, Almost no neck at all. Don't know what kind of barrel life he is getting but since the case is based on the 30BR case it is my belief that it does very well on barrel life.

I do not believe there is a case anywhere with a shorter neck than the Wolf Pup. That may just be the place to start looking for any anomoly.

Roland

 

[Steve Blair]

I do not believe there is a case anywhere with a shorter neck than the Wolf Pup. That may just be the place to start looking for any anomoly.
Roland

[br]
Neck length is not the only factor. The Wolf Pup burns a relatively small amount of powder relative to the bore.

 

[Hombre0321]

Yea might be so, but that wasn't the question now was it? Man asked about short neck's and there affect on barrel life. Besides I'm not sure I consider 41 Grains of H4198 to be a light load, in a case as small as the 30BR. Read That "I".

Barrel life and how short it "can" be is something we all just have to live with. Barrels are expendable just like Powder bullets and Primers. How that fits into your shooting discipline is another thing. For me personally I would Never trade long barrel life for accuracy, and I'm not suggesting that any would reading here would.

Roland

 

[Steve Blair]

Yea might be so, but that wasn't the question now was it? Man asked about short neck's and there affect on barrel life. Besides I'm not sure I consider 41 Grains of H4198 to be a light load, in a case as small as the 30BR. Read That "I".

Barrel life and how short it "can" be is something we all just have to live with. Barrels are expendable just like Powder bullets and Primers. How that fits into your shooting discipline is another thing. For me personally I would Never trade long barrel life for accuracy, and I'm not suggesting that any would reading here would.

Roland

[br]
The three cartridges mentioned by the O.P. have similar case capacities, use similar powders, and are a fair comparison. You actually introduced a very different example that does not compare to the initial examples. So, it is a bit of a non sequitur. Even so, the .30 BR, with a longer neck and less capacity, probably has better barrel life than the Wolf Pup.[br]
That said, I agree that barrels are expendable. I have three finished, spare barrels waiting their chance and seven blanks with another on the way. I (mostly) avoid barrel burners because I don't live for the break-in and load development process. I would rather shoot a dependable barrel and load for a while before it is necessary to do it again.

 

[robbor]

Hey Taj im not laughing, there are reasons to do things and you should be justified in your reasons if just because thats what you want to do. I was looking for a smaller quieter cartridge for hunting when i remembered the article i posted. I was interested in a Vartarg but didnt like the case design of the neck, so i went with the 222. But have thought about doing a vartarg with a 222 neck and that would probably be enough to fix feeding issues also. thats my idea if someone steals it ;D.