pressure/velocity-clean brass v carboned

[rogn]

Did a brief search on this with no result. I have wondered about the differences in loads fired in clean shinny interior brass v. those with interior carboned. There would be some difference I would think due to the reflectivity of the clean brass versus the black carbon coated interior. One should keep the heat of combustion up in the case while the other might absorb some and lower pressure. Im not able to test this out at the moment so I thought Id as, anyone ever checked on this?

 

[bozo699]

Did a brief search on this with no result. I have wondered about the differences in loads fired in clean shinny interior brass v. those with interior carboned. There would be some difference I would think due to the reflectivity of the clean brass versus the black carbon coated interior. One should keep the heat of combustion up in the case while the other might absorb some and lower pressure. Im not able to test this out at the moment so I thought Id as, anyone ever checked on this?

rogan,
I have not tested your exact question but for loading wise using a force restoration setup on a K&M arbor press the difference is huge!... having the carbon left in only lightly brushed with a nylon brush is way easier and consistent also my vertical at 1000 yds was significantly reduced doing it this way. Since finding this maybe around 2012 I have never cleaned another inside neck.
Wayne

 

[powderbrake]

I agree with bozo699.
Also, after annealing, the carbon is gone from the inside of the neck, and seating is erratic unless necks are inside lubed.

 

[Rsadams]

You can also try something like imperial dry neck lube for new brass....

 

[dmoran]

Warning: topic hijack occurring....lol

Am in agreement with @bozo699 when it comes to case necks, but the OP is asking about the entire case internally.
While I haven't conducted actual pressure/velocity tests to the scenario, I have checked capacity variation of cleaned cases verses not cleaned. In one scenario, had an average of 0.6-grain capacity variation after a thorough internal cleaning of some 300-WSM brass that had 5-firings on them since new, which is more then enough capacity variation to also effect pressure/velocity.

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[CharlieNC]

I agree with bozo699.
Also, after annealing, the carbon is gone from the inside of the neck, and seating is erratic unless necks are inside lubed.

I also observed that the carbon appears to disappear after annealing, based on the color changing from black to a reddish/brassy appearance. But I don't notice neck seating variability and don't lube, only an occasional difference. This is an interesting aspect.

 

[rammac]

Any energy transfer would be of such insignificance that I doubt if anybody has ever studied it. There are far more important features to pay attention to.

 

[rogn]

Any energy transfer would be of such insignificance that I doubt if anybody has ever studied it. There are far more important features to pay attention to.

In other words you dont know either.

 

[rammac]

In other words you dont know either.

No I don't, but I do know how to search the Internet for information and without much effort I've found one paper, published in 1951 by the British Scientific Advisory Counsel of the Ministry of Supply, called "Internal Ballistics" which makes my point pretty well.

It states in Appendix II that:

Near the back of the chamber, where the gas velocity is always small...the total heat transferred to this region is relatively small, so the heat transfer by radiation has been completely neglected.

Previous to that they state:

The total heat-loss to the barrel...was found to lie between 4 per cent. and 9 per cent. of the total energy liberated...

So considering that the total amount of heat loss to the entire barrel is less than 10% of the total energy available and that they said that the loss in the chamber is so small that it wasn't worth investigating, I'd say that you wont find any studies on the topic because it's a waste of time.

 

[Straightshooter1]

In other words you dont know either.

I've been running a little experiment to see how much build up occurs over several firings. I'm finishing up on the 7th load without cleaning the interior and will then be measuring MV and case volume before I then clean the cases where I'll measure case volume again along with an MV to see what difference, if any, there might be. I'll be posting the results when done.

 

[rammac]

Technically the black inside the case isn't carbon, it's soot, there is a difference (I learned something while researching this stuff). Soot is made up of more than just carbon and it's typically made up of smaller particles than carbon.

Thermal Conductivity
Air (atmospheric gas) - 0.0262
Carbon - 1.7
Soot - 0.07
Steel - 30

The conductivity of steel varies quite a bit but 30 is an approximate average.

So, soot conducts heat 24 times less than carbon but about 2.5 time better than air.
Steel conducts heat about 430 times better than soot.

So since soot is a poor thermal conductor and steel conducts heat several hundred times better than soot, it's easy to see that the barrel steel would remove heat energy so much more quickly than the soot would. Between the speed that the gasses move away from the case and the heat conductivity of the steel, I think it's pretty obvious that the energy loss at the chamber would be comparatively inconsequential.

 

[bozo699]

Technically the black inside the case isn't carbon, it's soot, there is a difference (I learned something while researching this stuff). Soot is made up of more than just carbon and it's typically made up of smaller particles than carbon.


Thermal Conductivity
Air (atmospheric gas) - 0.0262
Carbon - 1.7
Soot - 0.07
Steel - 30

The conductivity of steel varies quite a bit but 30 is an approximate average.

So, soot conducts heat 24 times less than carbon but about 2.5 time better than air.
Steel conducts heat about 430 times better than soot.

So since soot is a poor thermal conductor and steel conducts heat several hundred times better than soot, it's easy to see that the barrel steel would remove heat energy so much more quickly than the soot would. Between the speed that the gasses move away from the case and the heat conductivity of the steel, I think it's pretty obvious that the energy loss at the chamber would be comparatively inconsequential.

That’s some serious studying!.... nice job
Wayne

 

[243winxb]

Cleaning brass in stainless tumbling media is important to consistency.
For example, we have noticed an increase in case capacity averaging close to 1 grain of water after cleaning previously fired .300 Win Mag cases.3

https://apps.dtic.mil/docs/citations/ADA572333

 

[rogn]

Rammac, Thank you for your research. 1951 research may be valid but seems to be based on opinion rather than documented instrumentation. I didnt see where they thought their "research" was pertinent to what. Anyone who has had a semiauto drop a case into their tee shirt or sock might question some of their hypotheses. What I was hoping for was some one who might have chronographed and compared velocities of identical loads in the two types of cases. I hoped this could be a simple request for first hand information. I didnt realize I had invited some pedant to demonstrate their superior intellect.
By the way, what is the thermal conductivity of bare cartridge brass.?

I have the feeling you jumped into this thread just to show me how smart you are, Ill grant you youre probably smarter than I. But the simple proposition as to whether there is actually a change in velocity has not been answered. I know there are more important issues like where do I get RE26 or Lapua punch or drill flash holes.
My apologies to any dealing with Alliant or Lapua.

 

[bozo699]

Interesting read!.... funny they found that almost seventy years ago and Hodgdon has done nothing to fix the problem.
Wayne