black powder chamber pressures.

sharpsguy

sharpsguy

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Hey guys,

Does anyone know what kind of chamber pressures you could expect from say 45-70, or 50-140? Whats the base pressure of black powder going off in a cartridge? Or the maximum pressure? I bet Moomcoon knows, as he's a pretty smart guy.

sharps guy.
 
For 45-70 my Lyman manual lists between 7,900 -14,600 CUP but it depends on the bullet weight and type of BP used.
 
Generally speaking, it normally is fairly hard to get much more than 15,000 psi out of Black, and that is roughly what a lot of the old rounds were rated at.

But all of this goes right out the window when you start really compressing the stuff. A .303 case holds 31 grains of Size 3-3/4 Cordite, plus a wad, plus the bottom of the bullet. It operates, in the Mark II Cordite cartridge, at 2,000 ft/sec and generates a maximum operating pressure of 16.5 Imperial (long) tons, or 36,960 pounds per square inch.
When loaded with a 70-grain charge of compressed Black powder in single-pellet form, the same cartridge and bullet runs at 19 Imperial tons per square inch: 42,560 pounds per square inch.
These figures are from "Text Book of Small Arms - 1909", Page 202.

I think it's fair to say that your pressures won't get out of hand until you start compressing the stuff.

Hope this helps.
 
Black powder loads should be compressed slightly. As far as actual readings, there is a couple graphs posted here http://www.canadiangunnutz.com/forum/showthread.php?t=249992&page=2 that show actual peak pressure readings for a few different loads, including a couple smokeless loads. If you look at the column titled 'peak', you'll see a list of three digit numbers. These numbers need to be multiplied by 100 to get psi. So, for example, the first number 193 = 19,300 psi.

As you look at the graphs, you will see that chamber pressures greater than 20,000 psi are quite normal for black powder 45-70 loads. You will also see why IMR SR4759 makes such a nice black powder substitute. From another article that I have, slower powders like IMR 4198, IMR 3031 and RL-7 give lower peak pressures than BP for the same velocity and bullet weights. You can also see from the graphs why Trail Boss, which is an extremely fast powder, is a bad idea in old BP guns, generating pressures well over 30,000 psi.

A general rule of thumb for estimating BP pressures for different BP cartridges is to look at a load table that had data for 2400 or IMR SR4759 and pick a load that gives the same velocity as BP loads, for the same weight cast bullet. The BP pressures will be pretty much identical to the 2400 or SR4759 pressures for that load.

I know that it is general knowledge that BP doesn't give much pressure, but that is simply not true on a couple different counts. First, is the tendency for BP to obturate the bullet, which requires a pretty hefty pressure spike. Second, are the actual chamber pressure measurements done and published by Sherman Bell. As Smellie pointed out, compressed BP does give higher pressures, and proper BP loading does require a certain amount of compression.
 
sharpsguy said:
Hey guys,

Does anyone know what kind of chamber pressures you could expect from say 45-70, or 50-140? Whats the base pressure of black powder going off in a cartridge? Or the maximum pressure? I bet Moomcoon knows, as he's a pretty smart guy.

sharps guy.
Click to expand...

The latest issue of the Black Powder Cartridge News magazine has some pressure data in it for .45-70. A couple of loads were tested and they ran in the 15k psi range.

I have some interest in the .50-140 as I shoot mine when I feel the need to develop a flinch :D. Alliant has a brief note about pressure in the .50-140, but they used a pretty light bullet at 550gr:

http://www.accuratepowder.com/data/...artridges/50 140 Sharps pages 371 and 372.pdf

Chris.
 
gunlaker said:
The latest issue of the Black Powder Cartridge News magazine has some pressure data in it for .45-70. A couple of loads were tested and they ran in the 15k psi range.
Click to expand...
What was the bullet weight and velocity and how many grains of black was used? In the link I provided in my previous post, a 45-70 loaded with 65 grains of FFg under a 500 grain bullet averaged 23,700 psi. This would be actually a little lighter than original 45-70 cartridges back when they used balloon head cases and could fit 70 grains of black. A relatively light load of 62 grains of FFg under a 500 grain bullet still averaged just over 21,500 psi peak pressure.

I've noticed that some published pressures don't seem to jive at all with actual pressure traces. I'm not sure why this is.
 
Win 38-55 said:
What was the bullet weight and velocity and how many grains of black was used? In the link I provided in my previous post, a 45-70 loaded with 65 grains of FFg under a 500 grain bullet averaged 23,700 psi. This would be actually a little lighter than original 45-70 cartridges back when they used balloon head cases and could fit 70 grains of black. A relatively light load of 62 grains of FFg under a 500 grain bullet still averaged just over 21,500 psi peak pressure.

I've noticed that some published pressures don't seem to jive at all with actual pressure traces. I'm not sure why this is.
Click to expand...

There were 2 loads tested:

405gr Lyman mould, Starline brass, 65gr of 1 1/2 Swiss, Fed LR primer, 0.060" wad. Averaged 12,431 psi. ES 1207 psi. Average vel: 1290 fps.

530gr Brooks mould, Starline brass, 65gr of 1 1/2 Swiss, Fed LR primer, 0.060" wad. Averaged 14,197psi. ES 1776 psi. Average vel: 1148 fps.

Pressures were measured with some sort of strain guage setup of a brand I haven't heard of (mind you I've only heard of one kind). The test rifle was a rolling block in .45-70.

These tests were mostly done to measure load consistency interestingly. An interesting article for sure. Although like many other in that magazine, it doesn't draw a lot of clear conclusions :D

BTW, I can still fit 70gr of Goex Cartridge in my C. Sharps with fireformed WW brass and only moderate compression (maybe ~0.2" or so) under a Postell style bullet. But the rifle has some freebore and permits seating the bullet out a bit. Mind you I can't do much more than about 67gr-68gr if I cover all of the lube grooves. :D

I must admit, I wonder about some of the data. I've heard some say they've seen .45-70 BP pressures over 30k CUP. I also wonder how well calibrated these strain guages are. It seems that you'd have to calibrate them for each rifle you test them on, with some sort of reference load. But pressure would still vary depending on chamber specifics, and who knows what else.

Chris.
 
10x said:
Are you sure those below 11,000 CUP are not LUP (lead units of pressure)?
Which lyman manual has B.P. loads?
Click to expand...

The Lyman Cast Bullet Handbook does (3rd edition). In interestingly, they did not see fit to shoot BP in the trapdoor section, just the Ruger only loads :).

The units are definitely CUP, and my manual shows loads running from 7,700 CUP to 16,900 CUP depending on bullet and powder charge.

Chris.
 
Win 38-55 said:
snip

I've noticed that some published pressures don't seem to jive at all with actual pressure traces. I'm not sure why this is.
Click to expand...

There are a large number of variables at play. Brand of black powder makes a difference, humidity, bullet diameter, the primer, and the gun itself to name a few.

There was one B.P. shooter who claimed to work for GOEX who said that the pressures and speed of burning of GOEX powder changed with the seasonal changes to the water supply. His claim was that GOEX made in the spring used surface water from a reservoir and gave less fouling than GOEX made from well water in the winter months.
Also each B.P. Manufacturer may have changes in the quality of components used while manufacturing each batch. Not to mention each manufacturer has their own formula. I have seen pressure tests on Curtis & Harvey B.P. compared to Dupont (now GOEX) and there were pressure and velocity differences between the two brands for the same volume of powder.

The other issue is that some pressures are measured in PSI (pounds / sq inch), some in LUP (Lead units of pressure) some in CUP (Copper units of pressure) and some pressures are measured with a piezoelectric sensor that probably gives a more accurate reading as it gives a pressure curve while the pellet crush pressure test gives peak pressure at the point the pressure is tested.

From all of the reading and shooting I have done the primer and humidity seem to play the biggest roll. On damp days the boom just isn't as loud with muzzle loaders. Damp days shouldn't affect cartridge guns as much.
 
gunlaker said:
The Lyman Cast Bullet Handbook does (3rd edition). In interestingly, they did not see fit to shoot BP in the trapdoor section, just the Ruger only loads :).

The units are definitely CUP, and my manual shows loads running from 7,700 CUP to 16,900 CUP depending on bullet and powder charge.

Chris.
Click to expand...

All of the research I have done on measuring pressure indicates that Copper pellets do not give reliable measurements under 9,000 CUP and that Lyman used LUP for pressures under 11,000 cup. They show both methods in the B.P. manual for muzzle loaders - switching from LUP to CUP at pressures over 10,000 - 12,000 LUP. They also established a lower limit for the CUP at 9000 CUP with the copper crusher pellets they were using. (Page 85 Lyman BP handbook, 1st ed). That does not preclude them from using a different (softer) copper pellet to determine lower pressures in the 3rd edition cast bullet handbook. Or it could be an error in compilation and editing of the data.

Also on page 235, the mold listed as 45712 throws a 330 grain bullet rather than 322 grains as listed. Also there was not mention of whether #2 alloy or pure lead bullets were used for the B.P. loads. Pure lead would cast out heavier than #2 alloy as well and that would change pressures - along with bullet hardness.
 
10x said:
All of the research I have done on measuring pressure indicates that Copper pellets do not give reliable measurements under 9,000 CUP and that Lyman used LUP for pressures under 11,000 cup. They show both methods in the B.P. manual for muzzle loaders - switching from LUP to CUP at pressures over 10,000 - 12,000 LUP. They also established a lower limit for the CUP at 9000 CUP with the copper crusher pellets they were using. (Page 85 Lyman BP handbook, 1st ed). That does not preclude them from using a different (softer) copper pellet to determine lower pressures in the 3rd edition cast bullet handbook. Or it could be an error in compilation and editing of the data.

Also on page 235, the mold listed as 45712 throws a 330 grain bullet rather than 322 grains as listed. Also there was not mention of whether #2 alloy or pure lead bullets were used for the B.P. loads. Pure lead would cast out heavier than #2 alloy as well and that would change pressures - along with bullet hardness.
Click to expand...

Those are interesting points indeed.

Chris.
 
One thing that properly compressed black powder loads do well is obturate the bullet, due to their high pressure spike. A lot of slower smokeless loads simply do not have the kind of pressure spike to do this. That being said, I am extremely doubtful that anything under 15,000 psi peak pressure will be sufficient to obturate the bullet. In fact, under 15,000 psi may not even expand the case to sufficiently seal against the chamber walls, with the result that the outside of the case will be sooty. I prefer to see a pressure curve if possible. That not only tells me the peak pressure, but the duration of any given pressure during burning.
 
Win 38-55 said:
One thing that properly compressed black powder loads do well is obturate the bullet, due to their high pressure spike. A lot of slower smokeless loads simply do not have the kind of pressure spike to do this. That being said, I am extremely doubtful that anything under 15,000 psi peak pressure will be sufficient to obturate the bullet. In fact, under 15,000 psi may not even expand the case to sufficiently seal against the chamber walls, with the result that the outside of the case will be sooty. I prefer to see a pressure curve if possible. That not only tells me the peak pressure, but the duration of any given pressure during burning.
Click to expand...

If you haven't seen it, the article in BPCN I mentioned earlier does show full pressure curves. Interesting to read, but it hasn't changed anything I do yet :D

Chris.
 
Thanks for that info, Chris. I'm heading into town tomorrow. I'll see if the local shooting store carries that magazine.
 
Well, then, likely that's why there are so many questions.

EVERYONE knows that you must use urine when you are mixing your powder. The BIG question is whether to use beer-drinkers' urine or wine-drinkers' urine. The solution is problematic, for beer-drinkers HAVE more urine, but anyone knows that wine-drinkers' urine is far superior.

I bow to your modern knowledge, gentlemen, and now will retreat back to the 15th Century!

Have you checked out a website called Musketeer.ch? Guy who runs it is a retired industrial chemist AND a shooter. Some really great stuff on his page, including how to load and fyr a gonne.

Have fun! That's what it's all about!
 
Well, the local shooting store has quite a few great shooting and bowhunting magazines, but it didn't have the BPCN one, so I'll just have to go back to my wife's 'To Do' list this evening.
 
Win 38-55 said:
Well, the local shooting store has quite a few great shooting and bowhunting magazines, but it didn't have the BPCN one, so I'll just have to go back to my wife's 'To Do' list this evening.
Click to expand...

I haven't seen it in stores anywhere unfortunately, so I bought a mail subscription to BPCN. It's published by Steve Garbe of SPG Lube fame.

I think there are 4 issues per year. It always has a few interesting articles in it, although I'll pretty much read anything I can get my hands on regarding BPCR :D

Chris.
 
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