Pressure ceiling of BP

[keith44]

I have a similar poll on another board.  This is intended as a safety discussion initiator.  On the other board so far only 60% of those who have responded / voted have gotten the correct answer.
 

[GGaskill]

Depends entirely on the circumstances.  If there is no way for the combustion gasses to escape, the pressure can probably exceed 100Ksi.

[keith44]

remember real black does not convert to gas as effeciently as smokeless.

[Cat Whisperer]

Didn't vote - it would have been a guess.
 
Black powder burns at the surface of the granule - the gasses emitted from the granule are limited by the pressure.  Therefore, in a sense it is self-limiting.  But to what extent?  In a sealed container vs. a container increasing in volume there COULD be a difference.  It is well known that in rifles the consistancy in velocity is right-much good because of this feature.  Smokeless powders burn more intensly with higher pressure, hence the greater difficulty in getting smaller deviations in velocities.
 
 

[Mike H.]

Well, cartridges like .45 Colt, .45-70 and so forth started life as black powder cartridges.  If I recall load charts showed something like 10,000 to 12,000 psi. Hence my vote for the second option.

[Double D]

How much black powder? In what volume? Totally contained?  Uncontained? 

[gunsonwheels]

Some time back someone's post referenced an Ordnance Manual from the 1800's.  I clicked on it and perused it until I got to a section on pressures and then read in detail.  Don't know where they got their data but they referenced several varying conditions of load and containment and I DO remember reading they, at least, said one of the conditions was well over 100,000 psi.

Matt Switlick did some "crushed cone" tests back in the late 60's or 70's but he limited his studies to trying to ID pressures typical to CW period ordnance so NSSA could limit original ordnance to a 2/3 of original working pressures (12,000 and 18,000 respectively).
 
I'd still like to see a properly strain guaged test tube so someone could produce some reliable data on containments, powder size/type and charge and the resuilting pressures.  I'm not much of a generous windage fan as I believe it is far more efficient to use a small amount of powder and let it push the full length of the barrel... and obviously that is exactly what rifled cannon (and all modern firearms) do as with snug fitting bolts or projo's there is NO escape of gases until the projo clears the muzzle.  But under those circumstances you have to have a pretty good indication if your metal, geometries and powder are or are not going to get you in trouble.  Nice thing about most steels is they elastically deform up to the yield point... and there is usually an amout of pressure above that they can stand before they will fail/burst.  I am also a fan of proof firing because with a $20 micrometer I can dimensionally check to see if my load exceeded the yield strength and the piece entered the plastic deformation range... and if the piece burst it is equally obvious I exceeded the ultimate strength.  Approach proof loads cautiously and verify the maximum load DID NOT exceed the YIELD strength (the upper limit of elastic deformation).  Bad news is if there is dimensional growth from a proofing, you MUST throw the piece away and start over with larger metal, stronger alloy and/or lower pressures.

GOW

[Parrott-Cannon]

Is this for BP contained in its own volume or for a cannon shooting a projectile?  I am currently working on a numerical method for calculating the pressure of BP contained in its own volume.  The first estimates was made by Noble and Able in the late 19th century.  One of the key factors in the calculation is the co-volume.  This factor corrects for the non-idea behavior of the gases produced when BP burns.  The more important question is what are the pressures produced during normal firing.

[Double D]

I have Switliks article on pressures and he used both copper crusher and  piezo electric pressure transducers in his testing.

 
 It's one thing to shot cannons that are antiques on the outside and modern gun-bore-rifling inside and get extreme performance at antique cannon ranges.  That is all about the competitive edge and nothing more.   It is quite another to shoot antiques cannons with antique bores and get that extreme performance.  I would find the latter more impressive.

[keith44]

Very good GOW!  The point is that some people believe (quite mistakenly) that with real black actual volume does not matter, that it cannot generate enough pressure to cause any harm to even the most antiquated of antiques.  They seem to for get that black was once used for blasting.

[keith44]

less than 60% wow.

[subdjoe]

As has been pointed out, old ordnance manuals show 100,000 psi or more 'possible' based, I believe, on the work of Able & Nobel in England.   Were they wrong? 

By "ceiling" do you mean under normal "working conditions" or "under special test conditions that you will never see outside a test facility?"

[gunsonwheels]

Here's the link to the Ordnance Manual:
 
http://www.archive.org/details/ordnancemanualfo00unitrich
 
and the info I was refering to is on page 473... at the bottom of the page.
 
BP in twice its volume is less than 50KSI... but two and one pounds in their volume are 133,590 psi and 185,000 psi respectively...  and that is with a .1" grain size (i.e. relatively coarse compared to FFFFg).
 
GOW

[Double D]

Very good GOW!  The point is that some people believe (quite mistakenly) that with real black actual volume does not matter, that it cannot generate enough pressure to cause any harm to even the most antiquated of antiques.  They seem to for get that black was once used for blasting.

Very true. Volume does matter.  If it didn't we could fire all guns with just one size charge.

I also believe it is black powder pressure that retains it pressure when it meets resistance until the resistance is over come either by the movement of the resistance or the failure of the resistance... (Some body correct me if I am wrong or correct the part I have wrong.)

Black blasting powder has a slightly different composition than black gun powder.  You can use black gunpowder for light blasting but it is not as efficient as black blasting powder=.

[Cat Whisperer]

The blasting powder is a little more gentle so it doesn't shatter the rock - important if you're using it in the granite quary.
 
 

[gunsonwheels]

This is just one guy's experience and his conclusions... any resemblence to the truth... well you know.
 
Back in the late 60's when I started shooting a 40mm, I was a starving college student and would pick up a 50# box of "B" blasting from Margraf Explosives in Rancho Cordova, CA when visiting the mother-in-law (after all the trip had to have some productive purpose).  We were paying about $65 for 100# (or maybe that was for the 50# box).  "A" blasting was rather thoroughly researched at that time as it was $85, made with KNO3 instead of NaNO3 for an oxidizer, had the same chemical composition as sporting powder (%'s of S, C, and KNO3) and with the granulation charts, one could figure out equivalencies between "A" and Sporting.  Densities were in different units but after running the conversion the densities were also fairly close 'tween "A" blasting and the "g" series Sporting grades.  I never could get "B" to swell a skirt of a mini-ball slug even though I tried different masses, alloys, skirt thicknesses and powder charges.  My mold had three different cavity plugs to vary skirt thicknesses and two rings that could be put around the plug to control the depth of insertion into the cavity and thus vary the mass and OA slug length (pics below).  "B" is (was) noticeably slower in the pressure rise than "A" or Sporting.  "A" is also called fireworks powder by GOEX and "B" was discontinued about the time DuPont quit the black business.
 
I still do most shooting with "A" blasting 4Fa which is very equivalent in all ways, including performance, to Fg sporting.  And it is usually 2-4 dollars a pound cheaper than sporting from the GOEX distributor.  The only bad news about "A" is there appears to be a wider spread in performance between powder lots... beings we can only get/buy a 50# box at a time, by the time we shoot that up, the distributor usually has a different lot of powder and it is necessary to re-evaluate it's perforance in relationship to the previous lot and vary the powder charges (or aim points) accordingly.  Again, the military has the same problem with their propellants and thus invented the velocity collars on all modern ordnance to rapidly ID the variance and automatically feed it into the fire control computer so he can comp their aiming points.
 
The good news about the Ordnance Manual info is it tends to verify what I found in experience... with KNO3 powder and a lead slug, the pressure must get pretty extreme at the bottom of the bore where the walls are thickest because I was able to get very reliable "upset" performance (the swelling of the skirt into the rifling near the bottom of the bore so it gets a good spin and stability before exiting the muzzle). 
 
DD:

I also believe it is black powder pressure that retains it pressure when it meets resistance until the resistance is over come either by the movement of the resistance or the failure of the resistance... (Some body correct me if I am wrong or correct the part I have wrong.)

Or in other words the projo moves or the piece explodes...??  That agrees with my experience. 

[keith44]

19th century experimenters Noble and Able documented pressures with black powder exceeding 100,000 psi.  These pressures were created in a laboratory setting not in muzzleloaders.  The results were verified by the US Navy in a seperate study. 

So of the 11 that played this little game 5 were correct.  It could be argued that 4 more answered close enough.  There are two that I hope take this to heart and carefully rethink how they load and handle black powder.

[gunsonwheels]

Reading the thread on armorer77 trying to blow-up a piece (referenced in the cannon/pipe-bomb thread) there was a reference to short loading (leaving a gap between the charge and the projo) and saying that would or could cause a catastrophic failure... that seems to fly in the face of the Ordnance Manual data saying 2# of BP in a volume of twice the powder's space only produced less than 50KSI where the same charge in its space produced over 100KSI.  But the data also indicates (not conclusively) that once the projo starts to move and begins to open the space, the ability of the BP pressure to go to the extreme levels is severely curtailed.