6.5 creed magnum

[Bluefish]

I see that.

But if you think about it, all the pressure has to come out the end of the barrel. It has no where else to go.

So it must just come out slower with a longer barrel, stretching out the peak impulse.

No matter the length of a barrel, the exact same total amount of energy must come out the end of the barrel.

See what I’m saying?

You are correct the total energy of the powder as to come out the barrel, but how much of the energy is in the bullet and how much is still in the expanding gases? If you take a say 60g powder charge and a 10” barrel vs a 20” barrel, what’s the difference in bullet speed? That difference in energy put into the bullet has to be contained by the can.

If run Quckload or GRT, they give the pressure left at the end of the barrel and how much powder is burned as a %. TLDR version is lots of powder and short barrels don’t burn all the powder and have higher pressure.

 

[omicron1792]

Thanks guys. Makes more sense now.

 

[HandgunHTR]

You are correct the total energy of the powder as to come out the barrel, but how much of the energy is in the bullet and how much is still in the expanding gases? If you take a say 60g powder charge and a 10” barrel vs a 20” barrel, what’s the difference in bullet speed? That difference in energy put into the bullet has to be contained by the can.

If run Quckload or GRT, they give the pressure left at the end of the barrel and how much powder is burned as a %. TLDR version is lots of powder and short barrels don’t burn all the powder and have higher pressure.

Another thing to keep in mind is a considerable amount of the "energy" is transformed to heat that is transferred to the barrel and is expelled at the muzzle. Not all "energy" is converted into momentum of the gasses or bullets, or "pressure".

That is why these discussions about "physics" and "energy" get dicey if all one has is a rudimentary understanding of physics and fluid dynamics.

So, getting back to what started this, Dan is implying that the uncorking pressure in these higher peak pressure cartridges must be higher because the peak pressure is higher. As you can see from the graph, that may or may not be true. For a cartridge that uses a slower burning powder, the peak is elongated and the slope of the tail is usually longer. This is why you want a longer barrel, so that that pressure can work on the bullet longer. However, in these newer cases that don't have a large powder column, you can use a faster burning powder, achieve a higher peak pressure, but it is going to drop off fast as that bullet moves down the barrel and the volume that available for the gases gets bigger (for a bit more information on why this happens look up Boyle's Law), and there is no continued burn to replenish those gases. So it is very possible that the uncorking pressure of a 300WM, 7PRC, or 6.5 PRC in a 20" barrel will be significantly higher than the uncorking pressure of a 7BC or 6.5+peak with that same 20" barrel length.

 

[R@crx37372]

We all know faster is deader is gooder. More gooder is betterer.

As a hunter killing critters between 30 yards and 400 yards, with the vast, vast majority inside of 250, how exactly is this helpful for me compared to a standard 6.5cm?

I would say there's a couple of advantages first you can push bullets much faster out of a shorter barrel, second there's a 155 fusion tipped and a 156 berger option that a standard creed cant push fast enough to make viable. A 155 grain bonded bullet at 2900 fps out of a 6.5 cm is a whole another level allowing for larger animals or larger margin for error.

 

[nm.otter]

in these newer cases that don't have a large powder column, you can use a faster burning powder, achieve a higher peak pressure, but it is going to drop off fast as that bullet moves down the barrel and the volume that available for the gases gets bigger (for a bit more information on why this happens look up Boyle's Law), and there is no continued burn to replenish those gases.

...and if powder is still burning (as it will be when shooting overbore cartridges from short barrels) the ejecta are screaming hot and still expanding inside the suppressor.

 

[The Guide]

I would say there's a couple of advantages first you can push bullets much faster out of a shorter barrel, second there's a 155 fusion tipped and a 156 berger option that a standard creed cant push fast enough to make viable. A 155 grain bonded bullet at 2900 fps out of a 6.5 cm is a whole another level allowing for larger animals or larger margin for error.

What do you mean that a brass cased 6.5 Creedmoor can't push a 156 to a speed that makes "viable"? My 22" Howa 6.5 Creedmoor pushes factory Berger 156 ammo @ 2528 fps. This means @ 2500' DA (just my local DA right now) it is @ 2000 fps @ 460 yards and 1800 fps @ 655 yards. That is way further than most people can shoot accurately at. The 156 class bullets are already a viable option for the 6.5 Creedmoor in brass cased factory loaded ammo. Hand load and get another 100fps and you'll be at 500 and 700 respectively. For most people the +PEAK cased ammo wont change their lives but it will sure make shooting in the wind easier and allow brass cased 22"+ velocities in shorter barrels.

Jay