Bore volume @ case capacity

[Ebjonnes]

Hello, Am I correct in thinking that it requires a specific length bore to burn a specific amount of powder?Like at some bore lenghth,a 30-06 could not better the velocity of a 308 with a identical bullet and powder, even though the o6 is a heavier charge? Thanks.

[Castaway]

Powder is burned within less than 3 inches of the barrel regardless if it's a fast powder like Bullseye or a slow powder like IMR 4831.  Any muzzle flash you see is not powder but super-heated gasses.  On another note, no 308 can exceed the velocity of a 30-06 given the same bullet, barrel length and operating pressure of the rifle. It's a matter of physics.  The 30-06 case holds more powder and consequently more velocity.  There's a rumor that a 308 is faster with the same bullet, but Speer did that one.  They tested and published the 308 loads with a longer barrel than the 30-06 and on paper it looks like it has the edge.   Ain't so.

[Robert357]

Powder is burned within less than 3 inches of the barrel regardless if it's a fast powder like Bullseye or a slow powder like IMR 4831.  Any muzzle flash you see is not powder but super-heated gasses.  

This is very interesting.  I was hoping that you might be able to answer another question.

If muzzle flash is super-heated gasses, then what is going on between shooting say a MN-44 and and say a MN1891/30.  The only real difference is barrel length and yet the shorter barreled rifle for a given load appears to have a much more pronounced muzzle flash.  

Is the longer barrel allowing the gasses to cool?  Is it that the gas exits at a lower pressure (i.e. larger volume due to longer barrel)?  I can understand that in a perfect gas pressure, volume and temperature are all interelated.

[PaulS]

If cartridge volume and pressures are the same the longer barrel will allow the gasses to cool more in the longer barrel more than in the shorter barrel. In the longer barrel there is more internal area to absorb the heat from the gas column and more time in the barrel adds to this effect.

[Steve P]

If these theories are correct, then after a barrel begins to heat up, the pronouned flames out the end of the barrel should become longer.  I have not found this to be correct, but then again, I may not be letting the barrel heat up to the point to prove this theory correct.

I will agree the muzzle flash is due to hot gasses, but the hot gasses are definetly the result of the particular powder you are using and it's burning characteristics in that particular gun.  i.e. bore and barrel length.  In the case of the Moisen Nagant, I would say the flash is internal in the longer barrel.  Still there, just not visible.  Try shooting a model 44 or 59 side by side with a model 91/30, after dark, with same ammo.  See if flash appears to extend at same distance from chamber.  

Steve  

[Robert357]

As a professional engineer, it is time to point out that Boyles law of gas says that

Initial pressue/Final Pressure  =  Final Volume/Initial Volume

Translated; the pressure within the cartridge of an MN44 is the same as the pressure within an MN1891/30 cartridge at moment of ignition.  The intial volume of both is the volume of a 7.62x54R case.  

The final volume of the MN1891/30 with it longer barrel is much greater than the final volume of a shorter barreled MN44.  That means that the pressure when the bullet leaves the barrel (moment of muzzel flash) with the MN1891/30 is much less.

In a perfect gas, pressure and temperature are proportional for a given volume.  While I would suspect that both the pressure and temperature of the gas at the muzzle of an MN1891/30 would be less than the MN44, I don't think that it is high enough to be luminecent.

I suspect that there really is flame associated with burning powder, but I am speculating.  I am trying to follow the discussion to see what makes sense.

[giturgun]

Have always wondered on this , most srguements ar in rifle length barrels.
   I have the loadbook on the tc contender and in the 30-30 section it has these max loads

     in the sierra bullet section
     gn                  bbl in inches              powder      gns      vel
   110                         10                      imr 4198    29.6       2200
      110                   14                       imr 4198      29         2300

    Why would the 10 inch barrel use .9 gns more powder and get less velocity,   And why do they list the max charge on the 14 as less,  this is from the sierra test labs so I would assume the data is correct

     also in the hornady info the barrels used to test were 10 inch  their statement is this  " uniformity from shot to shot is necessary for accuracy ...  uniformaty was never obtainable ..   the case capacity vs barrel length  the 30-30 case is designed to perform in a rifle length ,  ...  to much powder is left unburned which contributes to
poor accuracy.   "  They go on to explain when slower powders are used to burn better poor load density results.
     Now it seems to me that the powder companies say the powder needs at least some room to burn, and 10 inches is not enough    
     Also in the manuel the .222 is listed the same way 10 inches is to little to burn the charge, I contend that not all the powder will be burned in a short barrel  , and if all powder could be burned in shorter distances  we could do with less variation in powder burn rates.    

   On my own loading experiments I have noticed this , in my 14 inch contender in .222 rem.  I can use the max charge listed in the manual and the slower powders do seem to flash more, this is also true in the 30-30 16inch and the 45-70 14 inch barrel ,   I have used data from the 30 herret using filler to try and even out the shot to shot varience but with not much sucess.

[Steve P]

As a professional engineer, it is time to point out that Boyles law of gas says that

Initial pressue/Final Pressure  =  Final Volume/Initial Volume

Translated; the pressure within the cartridge of an MN44 is the same as the pressure within an MN1891/30 cartridge at moment of ignition.  The intial volume of both is the volume of a 7.62x54R case.  

The final volume of the MN1891/30 with it longer barrel is much greater than the final volume of a shorter barreled MN44.  That means that the pressure when the bullet leaves the barrel (moment of muzzel flash) with the MN1891/30 is much less.

In a perfect gas, pressure and temperature are proportional for a given volume.  While I would suspect that both the pressure and temperature of the gas at the muzzle of an MN1891/30 would be less than the MN44, I don't think that it is high enough to be luminecent.

I suspect that there really is flame associated with burning powder, but I am speculating.  I am trying to follow the discussion to see what makes sense.

Robert,

I don't think Boyles law of gases, as stated in your equation, applies here.   It may apply in calculating volume/pressure needed to fill a specific capacity, but it does not apply, as you stated, in ballistics.

It has been proven time and again, that barrel length has a basis on velocity of a given load.  You have pressures created within the cartridge as it fires, friction from the bullet travelling down the barrel, pressures within the barrel as the bullets accelerates, etc.   A Moinson Nagant 7.62x54R with 20" barrel will not have more pressure than a 91/30 with 27" or 29" barrel.  The pressures being created within the cartridge and within the barrel as the bullet accelerates do not build as much prior to the bullet exiting the barrel.  The 20" MN will have less velocity and less pressures.  The 91/30 with longer barrel builds pressures longer as the bullet accelerates the additional 7" or 9" and actually has greater pressure and higher velocity.

I tried to find a recent article on the .17M2 that started off with short vs long barrels, then, using a longer barrel, they started cutting off one inch of barrel at a time to find optimum velocity.  It would really explain this better than I.  In the longer barrels, the pressures no longer continue to build and the coefficient of friction of the bullet going down the barrel starts to take over when the pressure maximizes.  The bullet will actually start slowing down.

Steve  

[Robert357]

Steve;

I would agree that friction plays an important point in bullet velocity, but I thought we were talking about whether "muzzle flash" is burning powder as some contend, or "hot gases" as other contend.  Sounds like an interesting article on the .17 rim fire and finding the optimal barrel length.  If you find it, it would be a fun read.

My comment was to try to play devils advocate on the "hot gases" being the source of "muzzle flash" and see if that made sense from the perspective of the laws of chemistry.

I don't know what is causing the bright orange I see when I view a muzzel flash, but I am curious as to what might be the cause.

[Steve P]

I have heard that slower burning powder has chemical additives to retard and/or equalize the burning rate.  I don't which chemical this is, but it is suppose to be that added chemical or chemicals that is producing the brightly colored flames we see.  Fun one is the surplus 2230 from AA.  Makes about a 3 foot flame in front of a 10" Contender barrel in 30-30.

Steve  

[giturgun]

Powder is coated with something to slow it down and the grain shape and size has an effect on burn time as well . When I was in the mil . in the late 70's I was a 13 b 10 L9   HOWITZER CREWMAN OR CANNON COCKER. The m 109 sp fired a 155 round  , the distance was determined by a combination of angle of fire  or elivation of the gun and the number of powder bags used. the primer was a 308 blank which fired into a bag of very fine powder , as the piowder bags were stacked the grains were also larger , the last being about the size of my pinkie . The 8 inch and all the navel guns of big bore are the samr way. as the powder burned the progression of burn was controlled by the grain size and coatings.  
 After I came out of the service I did pipe welding and inspection for some time. During this time I did some inspection at the ammo plant in Radford V A  on the powder line . Seems like the nitro used in single and double base powders will cause severe headaches and ultimatly brain damage, we inspected a system to draw fumes away from the sewing machine operaters . They still make those powder bags the same way they were made during ww1 and 2     . Now the next time you open that new jug of powder if your like me you'll suck some up your nose , I actually like the smell       Powder is progressive burning and burns faster to a point as pressure builds, old black powder was a consistant burn, burned the same rate as pressure increased :twisted:   be kool

[goodconcretecolor]

I am a chemical engineer and an avid reloader for 18 years. Internal ballistics has always been an area of great interest to me. If you look at occilloscope traces of chamber pressure, the peak pressure is reached when the bullet is only a few inches down the barrel. from that point on, Boyles law would apply. By the laws of thermodynamics, after that point, as the pressure drops, so does the tempurature. It is reasonable to assume that after the peak pressure point that most of the powder has combusted. Therefor muzzle flash would be the product of incandescent powder gases rather than burning powder. As the pressure and temperature drop, the glow of the gases will drop.
All the above is based on the same load in different length barrels. Slower powders will tend to give more flash. Some powders are formulated to reduce flash but how they do this, I don't know.

[Castaway]

One technique is to add CaCO3 to reduce muzzle flash.  Don't think that is what we do, but the Chinese supposedly do it to their equavelent of 3031

[PaulS]

There are a number of additives and coatings in and on smokeless powders. Graphite is used to retard flame propagation and things like calcium chloride to stabilize moisture and a host of others.

Dibutyl phthalate
Polyester adipate - buffer?
Rosin - retardent?
Ethyl Acetate
Diphenylamine
N, Nitroso diphenyl amine
Potassium sulfate
Tin dioxide - retardent?
2-Nitro diphenyl amine
Potasium Nitrate - oxydizer?

These in addition to the Nitrocellulose and in double base powders nitro-glycerine. I can only guess at those above.


If anyone know what all these chemicals are for then you can post them