When powders run out of barrel?

[Shrinkmd]

I've heard that you can stop getting increases in velocity despite increasing charge if you "run out of barrel," especially with a slower burning powder like 2400. I had previously made up .357 Magnum loads with both 125 JHP and 158 LSWC, and despite staying well under published max loads, I stopped getting additional fps above 16 gr 2400 in the .357 (I went as high as 17.0, and most books and Alliant say 17.5 to 17.7 for max).

These were in 5" barrels. If I shot them in a rifle like a Marlin 1894, would I likely see the difference since the slower powder can burn more completely? And if this is true, does it argue for using a somewhat faster powder in dedicated revolver rounds? It would be nice loading less powder for the same result. How about Power Pistol or Unique? I'm primarily thinking about this phenomenon in .357 Magnum.

 

[Walkalong]

Longer barrels make use of the pressure for a longer time, even though the pressure is subsiding, thus giving more velocity. They do this for light charges of fast powder as well as big charges of slow powder.

The fastest load in a short barrel will be the fastest in a long barrel, and the slowest in the short barrel will still be the slowest in a long barrel, but naturally they will both be faster in the longer barrel.

Sure, you can download a slower powder to match the velocity of another faster powder in a 5" barrel, but is isn't the barrel length, it is the lesser amount of powder being burned. ( Energy being released, and for a shorter time))

 

[MtnCreek]

Question: Is it possible to reach a point where a cartridge is below max powder charge, but no more velocity can be achieved because the short barrel cannot make use of additional powder?

Thanks!

 

[Walkalong]

Not with most powders, but you will find a point of diminishing returns where you do not get any reasonable velocity increasing for the amount of recoil and powder burned.

Some powders, Solo 1250 in 9MM or .38 Super for instance, will start losing velocity when compressed. Go figure.

 

[Jasper1573]

+1 for Walkalong's comment concerning

a point of diminishing returns

When I first started reloading .308, I began down around 40 grains of Re-15 and worked my way up to 44 grains, only .3 grains below the max load in the Lyman book.

Yes, the 44 grain load gave me an additional 100 or 150 fps over a 43 grain charge, but because of the powder burning outside of the barrel (so I have been told) the amount of recoil increased dramatically and accuracy didn't improve, but suffered a bit.

It made no sense to beat myself up with a less accurate load that used more powder than my 24 inch barrel was able to effectively burn.

 

[warnerwh]

I don't understand how powder burning outside of a barrel would effect recoil. That just doesn't make physical sense. Adding more powder and sending the bullet faster would indeed increase recoil but that is due to the fact that for every action there's an equal and opposite reaction.

 

[GLOOB]

Some of the extra powder burns inside the barrel, and the gases exit rather quickly. Some may leave as unburned flakes, and even though the powder is much lighter than the bullet, the gases exiting behind the bullet leave at a much greater velocity than the bullet. If those gases are carrying unburnt powder, the extra mass could affect recoil, as well.

The action/reaction is a big part of the equation, but not the whole thing. Otherwise muzzle brakes wouldn't work.

 

[warnerwh]

I thought of that too but it doesn't seem like it would be enough to make a significant increase of recoil. What he describes sounds like quite a difference. However I've been wrong before.

 

[DickM]

I don't understand how powder burning outside of a barrel would effect recoil. That just doesn't make physical sense. Adding more powder and sending the bullet faster would indeed increase recoil but that is due to the fact that for every action there's an equal and opposite reaction.

Recoil is a function of not just the bullet mass and velocity, but of the entire mass being ejected from the barrel (termed the "ejecta"), which includes the powder, whether burnt and therefore in the form of a gas, or urburnt and whole. (When powder burns and is converted to gas, that gas retains the same mass that it had in its unburnt form.)

For pistol cartridges, where the mass of the bullet is (generally) far greater than the mass of powder, the additional recoil due to the powder fraction of the ejecta is minimal, but for many rifle cartridges the powder comprises a significant portion of the ejecta and therefore contributes considerably to the recoil effect. So, additional powder in the cartridge will increase recoil even if it doesn't have time to burn and contribute to bullet velocity.

 

[moxie]

Unique works great in .357 mag loads, short of the real screamers where 2400 excels.