BP VS smokeless pressure curve and effects on guns?

Discussion in 'Blackpowder' started by gilgsn, Dec 8, 2017.

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  1. gilgsn

    gilgsn Member

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    Hello,

    We all know not to use smokeless powder in an old BP-only gun... I won't do it, I swear.
    I wonder however why that it... BP burns faster and has a fast pressure rise time. It would seem logical that smokeless would be less harmful to old guns, assuming equal pressures.
    Do old guns blow up because people use too much smokeless? I assume there has to be another reason... I did read that old shotguns blew up because the barrel would thin out too soon from the chamber, but what about a revolver? A revolver barrel is much thicker than a cylinder chamber and there is the cylinder to barrel gap... So why would a cylinder fail with a slower burning powder and a load producing a pressure within the original BP specs? Is it because the pressure is applied for a longer period and the steel has more time to expand beyond its elastic limit?

    Gil.
     
  2. Mizar

    Mizar Member

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    Are you sure about that? Just because smokeless burns slow in an open space does not mean that it will do the same in a cartridge case... Gunpowder burns slower and rises pressure more gradually than smokeless.
     
  3. Crawdad1

    Crawdad1 Member

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    I don't think that's correct either. Regardless, smokeless powder creates way to much pressure.
     
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  4. alsaqr

    alsaqr Member

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    NO. Old muzzleloaders blow up because folks use "smokeless powder": Period. The term "smokeless powder" covers a lot of ground from slow burning rifle powder to very fast burning shotgun/pistol powder. In the 1960s a friend and i deliberately blew up a couple dozen old conventional muzzleloaders using smokeless powder.

    This guy blew up a modern inline muzzleloader using a measured charge of shotgun powder that he removed from 20 gauge shells:

    https://www.facebook.com/icodistrict7/photos/pb.1495007814108462.-2207520000.1418743310./1510799485862628/?type=3&theater
     
  5. J-Bar

    J-Bar Member

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  6. Jim Watson

    Jim Watson Member

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    Sherman Bell did a lot of work on smokeless powder in Damascus shotguns for the Double Gun Journal.
    A guy here found some pressure curves like Texas Mac's and used them to justify his low pressure smokeless loads for his Damascus guns.
    I would like to put them in a sack with Slamfire and shake them up.
    But you can find a lot of busted shotgun barrels.

    David Chicoine said smokeless powder gave greater wear and tear on the old guns. That he started getting a lot more S&W top breaks with stretched frames and broken latches when people took them to shoot Cowboy and did not want to clean up black powder. Of course the other factor was that they were SHOOTING them on a frequent basis which is something very few of our forebears did.
    I sold my top breaks to collectors so I wouldn't have to make a choice.
     
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  7. mcb

    mcb Member

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    There is no doubt you could create safe loads with smokeless powder that would generate lower pressures than BP. Trailboss is a great example. It is a relatively fast burning powder but is supper low density so you can't get much in the case. It works great in old blackpowder cartridges like 45 Colt and 38 Special to keep pressures low while burning completely and cleanly. You could still blow up an old gun up with it if you try, but if you are careful you can certainly create a cartridge with modern smokeless powders that would be safe in a blackpowder gun. It would not be a trivial matter but certainly a do able project if you had the right equipment like a instrumented pressure barrel, good software and a fair amount of experience.

    A safer alternative is to use modern propellent specifically engineer to replace BP. Pydrodex and the growing variety of black powder substitutes are modern propellants designed to be used in BP guns.
     
  8. Mizar

    Mizar Member

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    Interesting article, J-Bar. While not arguing about the data, I have a problem with the following comment from the same article:

    “Black powder burns at essentially the same rate regardless of increasing pressure in the chamber or cartridge. Therefore the burn rate and pressure curve rise times are independent of
    the pressure levels.” Smokeless powders are generally progressive burning powders, meaning that as the pressure increases the burn rate increases. So the leading edge of the BP pressure curve will rise rapidly in a linear fashion compared to the leading edge of smokeless pressure curves, which will have more of a non-linear shape and rise slower."

    So, how come with increasing burn rate for smokeless, one will get the pressure to rise slower? To me it seems to be exactly the opposite.
    The diagram bellow, from Driftwood Jonson, shows pressure curve for smokeless that is in direct conflict with the above paragraph. Sure, it's for a different powder (and firearm), but makes much more sense regarding the progressive burning comment.

    pressure_curve.jpg
     
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  9. ofitg

    ofitg Member

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    As I understand it, smokeless (ie, nitrocellulose) powders have an auto-ignition/cook-off temperature around 300 degrees F, while blackpowder has an auto-ignition temperature up around 600 degrees F.

    Confined in a chamber, the rising pressure and adiabatic heating will cause all of the smokeless powder granules to ignite at ~300 degrees F, while a confined blackpowder charge is still transferring the fire from granule-to-granule at that temperature.
     
  10. J-Bar

    J-Bar Member

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    Mizar;

    I’m glad you found that chart. I looked for it but could not find it. I agree the article I posted generates more questions.

    DJ’s graph shows them both peaking at about the same time.
     
  11. MEHavey

    MEHavey Member

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    Would you believe.... reversal
     
  12. D. Buck Stopshere

    D. Buck Stopshere Member

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    As some folks prior to my post have done, my friend took a old Pietta 1860 Army revolver and loaded only one chamber with the equivalent of a 25 ACP load, 1.5 grains of Bullseye powder, by weight, and seated a lead round ball on top. He clamped the revolver in a vise outside in the backyard brick grill. Covering both openings of the grill with steel plates, he tied a 30' string, stood back that distance, and "pulled the trigger" (remotely). The photo shows the power of just 1.5 grains of Bullseye smokeless powder, which is, I think, one of Alliant's fastest burning pistol powders. It should be pointed out that modern cartridge revolvers use a harder steel. The R & D cylinders are manufactured from 4160 Ornance steel.

    I use it in a static display at gun shows to show, hopefully, the pitfalls of folks, who's first (& perhaps, last) words might be, "here, hold my beer, watch this."

    RQ5A4210.jpg
     
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  13. 45 Dragoon

    45 Dragoon Member

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    I'm pretty sure bp is the slowest burning powder, which would result in the familiar "push" and a boom! The "punch" recoil and "crack" report of smokless denotes a more abusive force to deal with which is directly related to what lead to my current career!!

    This is what lead me to the "close tollerance" setup for our beloved cap guns!

    Mike
     
  14. Crawdad1

    Crawdad1 Member

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    Its black powder that burns at an incredibly fast rate. Lay a separate line of smokeless and black powder out and touch a match to them. The black powder is gone before you can blink your eye while the smokeless is still burning.

    Its not the burn rate its the pressure developed going from a solid to a gas.
     
  15. MEHavey

    MEHavey Member

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    No. BP is incredibly Sloooooooooooow compared with smokeless in any functional design use/any confined cartridge space
     
  16. Officers'Wife

    Officers'Wife Member

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    Yes and no... I've been told of another explosive (C4 I think) that you can light with a match and use it to brew coffee. Keep in mind that smokeless powders are a mixture of nitrocellulose and nitroglycerin so are essentially dynamites. While in the open air they will burn relatively slow, when confined the pressure wave is enough to cause disassociation and creates a true detonation with is generally measured in feet (or meters) per second.
     
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  17. Crawdad1

    Crawdad1 Member

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    OK, learned something today. :)
     
  18. Jim Watson

    Jim Watson Member

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    C4 (Mostly RDX) is not sensitive to heat or Impact. Has to have a good blasting cap at least.
    You do NOT want a propellant powder to detonate. Deflagration is the normal process.
    SOME Smokeless powders contain both nitrocellulose and nitroglycerine, others only nitrocellulose. Double base powder can be detonated. The British used Cordite in demolitions. Some Good ol Boys hereabouts claimed to have put a blasting cap in a can of Bullseye (40% NG) and got it to go high order, blasting out a stump. But I wasn't there.
     
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  19. ofitg

    ofitg Member

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    How I interpret it - Looking at the graph in post #8, and assuming the time-scale numbers to represent milliseconds -

    The blackpowder pressure increases more rapidly for the first couple hundred microseconds.

    During the first couple hundred microseconds, the smokeless/nitrocellulose granules would be transmitting the fire from grain to grain (more slowly than the blackpowder burn, similar to what we would witness in "open air" burn comparisons). As the pressure rises, adiabatic heating causes the temperature to increase.

    The smokeless pressure curve suggests that at T+300 microseconds the temperature has finally reached the auto-ignition temperature of ~300 degrees F - the majority of the granules (which were not already burning) would ignite at this time, resulting in the rapid pressure jump.
     
  20. gilgsn

    gilgsn Member

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    All very interesting posts, thanks guys. However not one answers my question as to WHY do BP guns blow up with smokeless powder and not black powder... What is the difference between a seemingly appropriate smokeless charge pressure wise, and a BP charge? What is the difference that would make a gun blow up between a smokeless and BP charge generating the same pressure?

    Gil.
     
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  21. Mizar

    Mizar Member

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    Different steels have different properties. BP guns in general use low grade & low alloyed steels because the pressures generated by black powder does not require the high tensile strength needed for smokeless loads.
     
  22. J-Bar

    J-Bar Member

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    Part of the equation is projectile weight/inertia. The sharp spike using smokeless doesn’t give the big heavy muzzleloader projectiles time enough to get moving down the barrel. In effect, it creates a pipe bomb.
     
  23. whughett

    whughett Member

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    So now I need to ask, 45C cartridges loaded with smokeless for use in a modern double action revolver, S&W 25 in my case, safe to use in my ROA and R&S with conversion cylinders. Does that soft brass case make that much difference, the steel in the conversion cylinders much stronger. So far neither ROA or R&S have shown any adverse effect. I load in the moderate zone on all reloads regardless of caliber.
     
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  24. rdstrain49

    rdstrain49 Member

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    Gil, Mizar even drew a picture for you. What do you not understand about smokless powder = high pressure & black powder = much lower pressure?

    Bottom line don't do it.
     
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  25. whughett

    whughett Member

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    The chart would seem to refute that, the time frame for pressure spike was about the same, just the pressure was much higher in the smokeless.
     
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