Why is Black Powder so Hot?

  • 348 Views
  • Last Post 16 December 2019
Squid Boy posted this 14 December 2019

As I said, I am relatively new to cast bullets and black powder but I have been loading smokeless for over fifty years. Since I started with BP I have never read an explanation as to why my guns get sizzling hot after just a few shots with BP and hardly get warm with smokeless. It seems contrary since the heat of combustion is so much higher with smokeless and even the slowest powders don't get the barrels as hot. What's the physics and chemistry behind this? Thanks, Squid Boy 

"Squid Pro Quo"

Attached Files

Order By: Standard | Newest | Votes
rhbrink posted this 14 December 2019

When I got into BPCR Silhouette I found out how hot and how quickly they do get hot 5 to 8 rounds in a 5 minute period and that barrel is HOT! I was shooting a 45-90 with 88 to 90 grains of powder 535 grain bullet my thought was the large amount of powder compared to modern powder and the dwell time as these guns shot much slower so all that hot gas has more time to react with the steel barrel? 

Just my guess for what that's worth from an old Missouri squirrel hunter!

RB

Attached Files

R. Dupraz posted this 14 December 2019

More fuel, more heat and bigger bill, Least that's how my furnace starts working about this time of year, every year. 

 

R. 

Attached Files

  • Liked by
  • JeffinNZ
  • delmarskid
Squid Boy posted this 14 December 2019

All thought provoking ideas and maybe it will lead to the answer but I did some more digging and came up with these numbers. Most data I found lists BP at 3000 KJ/Kg with a solid density of 1.7 grams per cubic centimeter. That's kilo Joules per kilogram or the heat output of a kilogram of BP. The solid density is basically the weight of a cubic centimeter of stiff. At least that's my lay interpretation of it. I just picked IMR-4895 as an example because it was easier. The heat is 4080 KJ/Kg or a little more than a thousand joules per cubic centimeter with a solid density of 1.62 grams per cubic centimeter. So 4895 is only about one tenth of a gram lighter density wise but over a thousand more joules of heat content. My own personal experience tells me it is heat that pushes the bullet because heat = pressure. Simplistic maybe but I haven't seen were it goes wrong yet. So yes you would use less smokeless to get the same payload velocity as BP. Now here is where the light bulb seems to have lit. Payload includes the weight of the gas evolved plus any solids left over. BP, I believe leaves about 60% as solids, smoke particles mostly and so you need much more BP to get things going because it's not just the bullet you are moving. More powder is more heat and some of it is used to move the combustion by-products instead of the bullet. Barrel time may be another factor. Most smokeless loads are very fast with short barrel times compared to BP/cast bullet velocities. Giving a longer time to heat the barrel. Does any of this make sense to you guys? Thanks, Squid 

"Squid Pro Quo"

Attached Files

  • Liked by
  • BudHyett
  • M3 Mitch
Squid Boy posted this 15 December 2019

Well that sure got things heated up so to speak. I am still trying to really figure out the heat transfer to the metal and these are all good ideas to ponder. I had some experience with a 475 A&M burning over 100 grains of 4320 with a 500 grain bullet that didn't seem to get as hot as quick as my 50-90 burning 100 grains of 1-1/2F Swiss and a 500 grain bullet. Now, from the numbers the black doesn't have the same heat content as the 4350 (3890 KJ/Kg) so there is a good deal more heat in the same amount of powder. But the same weight slug leaves the barrel a lot sooner at 2500+fps compared to 1300 fps for BP. The barrel on the A&M was a lot lighter weight than the BP rifle so it had less mass to heat. Then the BP gun's barrel was 6 inches longer too and did that have an effect? A little more barrel time to transfer heat? So is it really barrel time that makes the difference? On the Garand op-rod thing, I ran two powders with the same bullet (180 grains) just to see. 50 grains of 4895 showed up as being 54,437 Pmax and 2,719 fps with a muzzle pressure of 8,074 psi. 55.5 grains of 4350 was needed to give a Pmax of 54,582 and velocity of 2,696 fps, close enough but a muzzle pressure of 9,054 psi. So the differences in burning rate are easy to see and one might think that the heat transfer to the barrel might be the same with barrel times being almost identical. The op-rod might object to the increased pressure though. So am I just rowing with one oar in the water on this? Thanks for your consideration and comments. The old ten legged mollusk, Squid Boy

"Squid Pro Quo"

Attached Files

  • Liked by
  • delmarskid
  • JeffinNZ
Squid Boy posted this 14 December 2019

Dupraz, I think Texas-mac is one of the better researchers/writers on the web today and this is one of the many that I have read. It explains the differences in the burning rates between the powders and the effect on obturation but not heating of the barrel. I have a Pressure Trace system that I use for higher pressure loading's and it shows the same traces. However, it doesn't explain just why the barrel gets so hot with BP. Quick Load and the Pressure Trace will show high pressures and therefore high heat out to the muzzle with smokeless but not so much with BP. You can see that in the differences with the slope of the trace after peak pressure. So just what is the difference? Might it be that the heat is concentrated near the breech with BP and spread out more with smokeless? Squid Boy

"Squid Pro Quo"

Attached Files

  • Liked by
  • BudHyett
Ken Campbell Iowa posted this 15 December 2019

be good to do a simple test with a temp gun ... same gun ... a 45-70 comes to mind ... and the same velocity ... say a 400 gr at 1300, 10 shots 30 seconds apart,  take the temp reading 30 seconds after last shot at same 4, 12, and 16 inches down the barrel .  first black, then smokeless, clean between.

then we might know IF ...

WHY might be more ephemeral ...

****************

could it be so simple as :: how many photons are created minus how many are blown out the barrel ??   all other minor variables would seem to favor black powder leaving a cooler barrel ( g ) ...

ken

 

Attached Files

  • Liked by
  • Ross Smith
Squid Boy posted this 16 December 2019

Ken, I think that may be the answer. As it will certainly prove the heating aspect but may still not show the reason. I have a Martini in 577-450 that I shoot in BP and smokeless. The bullet is a 405 Lee hollow base in paper patching for both but using 20 grains of Unique with polyfill or 80 grains of 2F to give equal velocities of 1330 fps. The Unique load will shoot under an inch at 100 all day. I can tell you the BP load gets hot quick and is not as accurate so I don't bother with it anymore. This cartridge/load situation is what prompted the question in the first place. I still haven't found anything that explains it fully. Is it 20 grains compared to 80 grains? Average velocity for the two is less than ten fps apart. The truth is out there. Thanks, Squid

"Squid Pro Quo"

Attached Files

  • Liked by
  • M3 Mitch
Ross Smith posted this 14 December 2019

I think you nailed it there, longer contact time in the barrel.

Attached Files

Wineman posted this 14 December 2019

Kind of like the bend your M1's Op Rod theory. 50+ grains of powder has more energy than does less than 50 grains. More BP has more energy than a smaller amount of smokeless.

Dave

Attached Files

Ross Smith posted this 14 December 2019

Basically sort of , BP releases all of it's heat all at once, whereas smokeless is progressive. This is as much a question as a statement.

Attached Files

rhbrink posted this 14 December 2019

Perfect sense to me!

RB

Attached Files

Brodie posted this 14 December 2019

It sounds good to me too you old ten legged mollusk.

B.E.Brickey

Attached Files

Wineman posted this 15 December 2019

Yep, your numbers support our theories and empirical results. The Garand example was that IMR/H 4350 by itself wont hurt a M1 op rod as long as you respect the 48-50 grain upper limit for the amount of powder. However, the bullet will not be going as fast as it would with the same amount of IMR/H 4895. Using more 4350 to get equivalent velocity gets more gas and more pressure still in the barrel at the gas port shoving the op rod harder. Your much larger quantity of BP heats things up faster.

Dave

Attached Files

BudHyett posted this 15 December 2019

I agree with Squid Boy for his heat released calculations and I may be supporting his theory. There is also a simplistic physical chemistry observation.

Most smokeless loads are in bottle neck cases that physically retain most of the powder charge in the case for ignition. Powder goes into the barrel, but the shape with the bottle neck keeps powder in the case or delays the powder to burn in the chamber area on its voyage down the barrel.

Black powder cases, most of which are straight wall, start moving the powder column as a roughly defined unit down the barrel as it is consumed. The high pressure column of black powder igniting is moving beyond the chamber as the powder column continues to burn, pressure and heat being incontrovertible. With the less than full ignition of black powder and the black powder continuing to burn in the barrel, the heat buildup continues as the bullet travels. 

 

Farm boy from Western Illinois, living in the Magical Pacific Northwest

Attached Files

Millelacs posted this 15 December 2019

Basically sort of , BP releases all of it's heat all at once, whereas smokeless is progressive. This is as much a question as a statement.

In the early '80's I shot some black powder and Pyrodex.  I read that when Pyrodex was certified the test was to put a blasting cap in a can of smokeless powder on a pallet of powder. and then set it off.  If there was a crater, that meant it blew up and was an explosive.  For the test for Pyrodex they and put a blasting can in every can of Pyrodex on the pallet and set them all off at once.  After the noise was over and smoke cleared there was no crater.  So Pyrodex was not an explosive and explosive transportation and storage requirements do not apply.

So, we are talking about a "controlled burn" with smokeless powder, and a (semi-?) "controlled explosion" with black powder.

Does this explain part of the difference in heat?

Food for thought?  Or just confuse the issue?

Attached Files

Ross Smith posted this 15 December 2019

M. I think so. (that really clearededed it up). To tell the truth I never noticed the difference, but then I only shoot holy black in my bp rifles and only shoot smokeless in my suppository rifles. Kinda comparing apples and horseshoes.

Attached Files

JeffinNZ posted this 15 December 2019

I agree with R Dupraz.  More fuel.  I know that burning 18-20gr of trap powder in the 12g is NOTHING compared to 75gr of BP.  Whoa Nelly the old double get warm in a hurry with BP.

Cheers from New Zealand

Attached Files

Close