Turbulence Point (TP) revisited

[jamesdmock]

It is with reluctance that I reopen this topic. While talking with Mike Ezell the subject came up and I told him that I remembered an article in PS from years back and I would try to find it. I found it and it is in the May, 1997 edition. The article was written by Ron Jeter, who I do not know.

He stated that P.O. Ackley may have been the first to look at this. Back in the 1990's a line of cartridges was developed that supposedly optimized the TP at 88% of the neck. The TP is the convergence of lines found by extending the shoulder angle. This was done to existing cartridges by changing the shoulder angle to direct the angular hot gases (with particles) to converge inside of the neck. For the line of TP wildcats 88% was chosen because that's where the PPC TP falls.

According to the author, the TP is not totally controlled by the shoulder angle. There are some cartridges that have a TP that falls in the neck without alteration. The .222 Remington has a TP that is 95 % out in the neck and therefore shows great barrel life and accuracy. The .223 has the same shoulder angle (23 degrees) but has a TP outside the neck (149%) due to a different length of the trimmed neck.

According to the author, decreased barrel life is due MORE to being overbore than to TP but found that the wildcat cartridges with the 88 % TP were very accurate.

I was going to scan some of the article, but the batteries are down in my scanner. I am just a messenger here and have not taken a position on this TP stuff...yet. Good shooting, James

PS
TP % = 1/2 groove diameter/ Sine of shoulder angle/minimum trimmed case neck length

 

[chkunz]

I am not an engineer and do not know if hot gases under pressure would react the same way. Just something to consider.

Good observation and worth considering but based on my knowledge of the subject the two cases are not comparable. One case would be somewhat comparable to incompressible, laminar fluid flow and is a very simple, constant temperature, adiabatic process and the other would be comparable to compressible gas flow but even more complicated; you have some solid being converted to a gas in the flow process, very complicated indeed.

 

[Cloudrepair]

It is with reluctance that I reopen this topic. While talking with Mike Ezell the subject came up and I told him that I remembered an article in PS from years back and I would try to find it. I found it and it is in the May, 1997 edition. The article was written by Ron Jeter, who I do not know.

He stated that P.O. Ackley may have been the first to look at this. Back in the 1990's a line of cartridges was developed that supposedly optimized the TP at 88% of the neck. The TP is the convergence of lines found by extending the shoulder angle. This was done to existing cartridges by changing the shoulder angle to direct the angular hot gases (with particles) to converge inside of the neck. For the line of TP wildcats 88% was chosen because that's where the PPC TP falls.

According to the author, the TP is not totally controlled by the shoulder angle. There are some cartridges that have a TP that falls in the neck without alteration. The .222 Remington has a TP that is 95 % out in the neck and therefore shows great barrel life and accuracy. The .223 has the same shoulder angle (23 degrees) but has a TP outside the neck (149%) due to a different length of the trimmed neck.

According to the author, decreased barrel life is due MORE to being overbore than to TP but found that the wildcat cartridges with the 88 % TP were very accurate.

I was going to scan some of the article, but the batteries are down in my scanner. I am just a messenger here and have not taken a position on this TP stuff...yet. Good shooting, James

PS
TP % = 1/2 groove diameter/ Sine of shoulder angle/minimum trimmed case neck length

Is that the sine of the included angle?

 

[seymour fish]

It is with reluctance that I reopen this topic. While talking with Mike Ezell the subject came up and I told him that I remembered an article in PS from years back and I would try to find it. I found it and it is in the May, 1997 edition. The article was written by Ron Jeter, who I do not know.

He stated that P.O. Ackley may have been the first to look at this. Back in the 1990's a line of cartridges was developed that supposedly optimized the TP at 88% of the neck. The TP is the convergence of lines found by extending the shoulder angle. This was done to existing cartridges by changing the shoulder angle to direct the angular hot gases (with particles) to converge inside of the neck. For the line of TP wildcats 88% was chosen because that's where the PPC TP falls.

According to the author, the TP is not totally controlled by the shoulder angle. There are some cartridges that have a TP that falls in the neck without alteration. The .222 Remington has a TP that is 95 % out in the neck and therefore shows great barrel life and accuracy. The .223 has the same shoulder angle (23 degrees) but has a TP outside the neck (149%) due to a different length of the trimmed neck.

According to the author, decreased barrel life is due MORE to being overbore than to TP but found that the wildcat cartridges with the 88 % TP were very accurate.

I was going to scan some of the article, but the batteries are down in my scanner. I am just a messenger here and have not taken a position on this TP stuff...yet. Good shooting, James

PS
TP % = 1/2 groove diameter/ Sine of shoulder angle/minimum trimmed case neck length

James, if this theory were not at least partially correct, would sandblasting work ?

 

[gunsandgunsmithing]

James, if this theory were not at least partially correct, would sandblasting work ?

Hello Charlie,

Partially? Like how much barrel wear happens at 8000° vs. 100° flame temp? Yes, I would agree that partially may be a good word.

Point being, that if wear occurs from an abrasive aspect, it's miniscule compared to the temps barrels are subjected to. JMHO, though.

Now, you do bring up an interesting analogy with a sandblaster. They have a ceramic nozzle that wears, but very slowly as compared to the part being blasted. True, it is ceramic for a reason but I think we can see the apples to oranges comparison where that logic is concerned. Anyway, this is sort of the point I was trying to make to James last night. Remember me trying to make an analogy with a balloon, James?

Yes, some powder will blow down the barrel too, but it IS what creates the propulsion also. Without the powder, there'd be no propulsion. So, does reducing the amount of powder reduce the abrasion? If so, it sort of defeats the argument that powder abrades the rifling away, substantially.

Also, take a 30br vs a 6br with nearly equal weight bullets. The 6 will use a similar but less amount of relatively slow burning powder.
The 30 will use a very fast powder..likely even a heavier charge than the 6. Yet the 30 will out live the 6 by several times over.
What gives here? One more thing. I have a lot of experience with a 30 Major(30 Grendel). It shares the same shoulder angle as a BR but has about .070" shorter neck. IME, with dozens of barrels, it lasts as long or longer than a 30BR. Lots of variables here to claim one is absolutely better than the other, conclusively..in any respect.

I don't know the answer but can guess with the rest of us. I opine that the vast majority of barrel life is dependent upon heat and duration.

I am very open to scientific data that will prove me wrong or right, although, I'm not sure it'll matter much as to what I shoot in competition.

--Mike Ezell

 

[Stan Taylor]

Hello Charlie,

Partially? Like how much barrel wear happens at 8000° vs. 100° flame temp? Yes, I would agree that partially may be a good word.

Point being, that if wear occurs from an abrasive aspect, it's miniscule compared to the temps barrels are subjected to. JMHO, though.

Now, you do bring up an interesting analogy with a sandblaster. They have a ceramic nozzle that wears, but very slowly as compared to the part being blasted. True, it is ceramic for a reason but I think we can see the apples to oranges comparison where that logic is concerned. Anyway, this is sort of the point I was trying to make to James last night. Remember me trying to make an analogy with a balloon, James?

Yes, some powder will blow down the barrel too, but it IS what creates the propulsion also. Without the powder, there'd be no propulsion. So, does reducing the amount of powder reduce the abrasion? If so, it sort of defeats the argument that powder abrades the rifling away, substantially.

Also, take a 30br vs a 6br with nearly equal weight bullets. The 6 will use a similar but less amount of relatively slow burning powder.
The 30 will use a very fast powder..likely even a heavier charge than the 6. Yet the 30 will out live the 6 by several times over.
What gives here? One more thing. I have a lot of experience with a 30 Major(30 Grendel). It shares the same shoulder angle as a BR but has about .070" shorter neck. IME, with dozens of barrels, it lasts as long or longer than a 30BR. Lots of variables here to claim one is absolutely better than the other, conclusively..in any respect.

I don't know the answer but can guess with the rest of us. I opine that the vast majority of barrel life is dependent upon heat and duration.

I am very open to scientific data that will prove me wrong or right, although, I'm not sure it'll matter much as to what I shoot in competition.

--Mike Ezell

Mike I may be in left field of what you're saying but the smaller the bore the more the erosion occurs that is why over bore cartridges don't live long because the amount of fire you're trying to shove down a small hole hope this makes sense.

 

[gunsandgunsmithing]

Mike I may be in left field of what you're saying but the smaller the bore the more the erosion occurs that is why over bore cartridges don't live long because the amount of fire you're trying to shove down a small hole hope this makes sense.

Fire? I agree. A larger bore likes faster powders that do equal work in less time. The larger bore allows for pressures and Temps to fall faster.
Right?

 

[jamesdmock]

One thing that I noticed in the article is that some cartridges were near the author's ideal TP without modification. Other than the aforementioned .222 was the .284 Winchester.

 

[Stan Taylor]

Fire? I agree. A larger bore likes faster powders that do equal work in less time. The larger bore allows for pressures and Temps to fall faster.
Right?

Yes no doubt