powder burn/barrel length

[Moe]

If you have a barrel long enough to burn all the powder in the case, do you still gain velocity if the barrel is longer? :shock:

[Possum]

No, the laws of science make sure that does not happen.

[Bug]

I'll go out on a limb, here. It's an arguable point from a couple of different viewpoints.
  The way I see it, the answer to your question would be yes. A still longer barrel can yield greater velocity. That is, the expanding gasses can still accelerate the bullet, even though there is no longer any active combustion going on. Diminishing returns are reached after a certain point. That is why some long-barreled rimfire rifles will give faster velocities, after the barrel has been cut off. I think optimum, for a .22LR, is said to be somewhere around 18". All the powder is accepted to be consumed in less than 12", but you continue to gain velocity up to about 18". The same principle applies to larger cartridges, just that we arent going to get to the point we will get diminishing returns - maybe a 4-5 foot barrel? >>>>>>>>>>>>>>>>>>>>>>>Bug.

[haroldclark]

Moe, if you have a certain cartridge and loading in mind, let me know and I will run it through my software program.  One thing that one should consider is that after all of the powder has been consumed, there is a point where the bullet starts to drag and lose velocity.

However, what makes the biggest difference in causing all the powder to burn or at least 99% of it is the selection of powder.  In shorter barrels, such as the Thompson 14 to 15 ", a slow powder like IMR 4064 will not burn in the barrels and ultimately produce less velocity.  H335 and BLC-2 both burn very close to completely in a 15" barrel.

It is rare, in my findings, that a complete burn in a 14" barrel takes place.  Some shooters declare that the muzzle flash is powder burning outside the barrel.  That could be true, but it is most likely the pressurized gas meeting the oxygen in the air just outside the barrel.  That is my Theory and I have not way to verify it.

I have tested 25 to 30 factory 357 Magnum loadings in my past studies for a police agency.  They were using the Remington 125 gr. go fast mama round.  I set up the firearm in a Ransom Rest and set up markings on cardboard background so I could measure the size of the "Flames" at the barrel and the cylinder gap.

We timed the trigger let off with a 35mm camera on a tripod in total darkness.  The flames lit up the entire room (we were shooting out the door at the range).  

The Remington load from a 4" Model 19 S&W was the fastest in velocity, the worst in recoil and a flaming screamer with a tear drop type of muzzle blast that was 20" in diameter and 3 feet long.  The flames at the cylinder gap were severe too.  We needed a load that when fired at night the Officers would not be blinded by the flash and give up their positions.

The most muzzles flashing round still provided the greatest velocity.  I was able to obtain nearly the same velocity with another loading with barely any flash.  I had to re-run the test due to disbelief that there was so little flash.

When the Remington Load was fired in a closed breech 10" 357 TC, the velocity increased immensely and there was less muzzle flash, but still more than desired.

The bottom line is that the powder will make all of the difference in longer barrels or short barrels.

I have studied the Encore 15" barrels in 30-06, 308 Win, 7mm-08 and 7mmBR.  Using standard loads in the 30-06 & 308 Win. with powders that are usually used in the cartridges, you will have a bunch of powder burning outside of the barrel.  Using H335 in the 7mm-08, you can work up a load that will burn most of the powder, give you the same (close to) velocity and the retained energy at 200 Yards as well as 500 Meters.  The recoil with the three cartridges will be the least with the 7mm-08 with all the performance of the other cartridges.

You will be amazed at the performance of the 7mm BR and the 7-Waters too, but that is another story.
Harold Clark
haroldclark@citlink.net

[Moe]

HC, thanks for your informative response. Yes I do have several in mind: the .357 MAX, and a Gary Reeder wildcat round, a.445 Super Mag necked down to .357. I am trying to determine the length I will need if purchased.
 Thanks again. The Max I am shooting is 140 gr bullet with 25 gr of H110.
Don't know about the Reeder cartridge.

[haroldclark]

Moe,

I don’t have any data on the wildcat 445/357.  25 years ago, a friend of mine chambered and patented the 357 Bobcat magnum (Bob Booth).  It was similar to the Baines & Davis 357.  They were both necked down 44 Magnums.  Your cartridge sounds interesting.  We used to get 2000 fps easily with 125-grain bullets from an 8.5” S&W model 27 revolver.  (Bob used special rings on the neck and shoulder to allow it to be fired in the revolver)

However, on the 357 Maximum, I can give you a bit of info.
Your load of 25 gr. Of H110 and the 140 grain bullet will burn 93.42% of the powder in a 14” barrel.  Bear in mind that this is a mathematical calculation based upon Neco QuickLoad software.  I have found it to be very close to real life.

A search turned up the following other data for your 357 Maximum.  The loads below are to be used at your own risk.  As always, start out lower than the listed powder amounts with your 140 grain bullet.  You may notice that there is no available data for the 140-grain bullet in the maxi.  The following data was worked up in Neco QuickLoad software in a
Thompson Contender with a 14” barrel.

20.5 grains of Alliant 2400
Velocity = 2117 fps
Powder burn in the 14” barrel is 98.3% (Very good)
Pressure of load is 42,008 psi and the maximum pressure is 48,000 psi.

18 grains of Alliant Blue Dot
Velocity = 2038 fps
Powder burn in the 14” barrel is 99.99% (Excellent)
Pressure of load is 38023 psi and the maximum pressure is 48,000 psi.

I have a 357 Maximum barrel too.  I use the 200-grain RCBS gas checked cast bullet.  I load 17 grains of IMR 4227 behind it and that provides all the fun that I can stand.  It does amazing things.  I have recorded many sub-minute of angle targets with it at 50 and 100 yards.  I have also, loaded it down to 13 grains of IMR 4227 with the same bullet.  The gun doesn’t care about the loading: it just keeps punching tiny groups.

Harold Clark

[Moe]

HC, sent you a PM.