Powder/barrel efficiency

[longwinters]

A question. My understanding is that the powder in a given rifle burns within the first several inches of barrel length. It is the pressure/gas that continues down and out the barrel.

Is this correct?

Long

 

[GISMatting]

The powder burns completely down the bore and out the muzzle several inches.

 

[steve4102]

The powder burns completely down the bore and out the muzzle several inches.

I am no expert on this or any subject, but it is my understanding that the powder is completely burned in the first few inches of the bore.

 

[Ol` Joe]

The powder burns completely down the bore and out the muzzle several inches.

I am no expert on this or any subject, but it is my understanding that the powder is completely burned in the first few inches of the bore.

That has been my understanding also. All the powder that is going to burn does so in the 1st few inches, the remaining unburnt powder and hot gas continues to work on the bullet for the rest of the barrels lenght. The flash one sees when the bullet exits the barrel is the oxygen poor gas reigniting on contact with the air, not still burning powder.

 

[GISMatting]

How technical are you getting? The powder itself only burns in the case... the flame is very large and it does extend out the muzzle... The powder contains all the oxygen it needs to burn in the case and propellant itself...

 

[Charlie-NY]

I am no expert on this or any subject, but it is my understanding that the powder is completely burned in the first few inches of the bore.

If this was true than why not make rifles with 3" barrels?

Generally speaking, as you shorten barrels there is a corresponding decrease in velocity. Lengthening barrels results in increased velocity. Powder burns progressively as the bullet travels down the barrel. If all the powder was burned in the first few inches than the friction along the remaining 20" of barrel, or so, would make the bullet slower as it dragged down the bore. This occasionally happens with a 22 rimfire when fired in a long barrel. The 22 rimfire has an extremely small amount of powder to be burned and it can be consumed in a relatively short barrel. But even the little 22 requires more than "a few inches" to complete the burn.

 

[steve4102]

Like I said, "no expert", but the burning of the powder is done in the first few inches and the expanding gases created by this burnt powder forces the bullet down the barrel. If the barrel is only a few inches long then the gases don't have time or distance to produce velocity . If the barrel is much longer then the gases (not burning powder) have time and distance to increase velocity before they are dispersed out the muzzle where they no longer affect the bullet speed.

 

[longwinters]

Like Steve says is what my understanding was. I wonder how people test this whole thing out. For any of us opinion does not necessarily equal fact.

Long

 

[rick smith]

steve is correct.Rick.

 

[Ol` Joe]

Velocity is the result of time under pressure.
The bullet jumps from the case with pressures rapidly rising from the burning powder until the powder is consumed and pressures are at peak. The bullet continues with residual pressure still pushing on the bullets base. The longer the barrel the longer the gas pressure will "push" on the bullet until barrel lenght reaches the point its volume equalls the gas mass and pressure is no longer high enough to positivly act on the bullet.

A small fast burning powder will rise to peak faster then a slower one. This is the reason less can be used in the cartridge compared to a slow powder. The larger amount of "slow" powder reaches peak later but has produced a larger volume of gas while doing so. This keeps the pressures higher during the bullets travel down the bore then would occure with faster powders and lower gas volumes. If you look at a graph of the pwder burn in a rifle bore the point of peak pressure is very close to the point of full powder burn.

 

[Charlie-NY]

Another thougt:

Why can you find unburned powder in the actions of autoloading shotguns that siphon gas off from the barrel to work the action? If all the powder was burned in the first few inches (or within the case) there would not be unburned powder available to be blown through the gas passageways and into the action. This may happen in gas operated rifles too but I do not own one so I'll only comment on what I have observed in shotguns.

When a powder charge begins to burn, not only is the bullet thrust foward, so is the powder column which continues to burn as it too is propelled up the bore.

While the original question refers to rifles, I would imagine that the principal is the same in shotguns.

 

[rick smith]

I think what you are seeing is powder that has burned but not completely consumed. Gather some up and try to light it up with a match as compared to unused powder.Rick.

 

[tjen]

In general diferent cases/cartridges need powders with diferent burn rates. With that said now for a given cartridge and a given bullet weight you can use a faster burn rate powder for better performance for a shorter barrel and a slower powder for a longer barrel which would give the highest velocity.

For example H4895 in my 18.5 " barreled 35rem has no muzzle flash when shot at dusk. How ever my 270win with any factory load shoots a 25" flame from its 22" barrel under the same light conditions. 270win uses slower powders like 4831 and R22 etc.

In that 35rem I can load a slower powder like TAC and as I increase the amout of powder you can see a point where more powder does not in crease the velocity because its not burned up before in runs out of barrel lenght and yep lots of flame and muzzle blast. Hope this helps a bit.

 

[GISMatting]

Another thougt:

Why can you find unburned powder in the actions of autoloading shotguns that siphon gas off from the barrel to work the action? If all the powder was burned in the first few inches (or within the case) there would not be unburned powder available to be blown through the gas passageways and into the action. This may happen in gas operated rifles too but I do not own one so I'll only comment on what I have observed in shotguns.

.

Neither my Remington 11-87 12 ga or my Ruger Deerfield 99/44 semi auto 44 mag rifle leave any unburned powder in the action. Both are gas operated. My 10/22 does leave quite a bit of unburned powder though.