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Jeff
Moderator: MudBug
Trapaddict wrote: New to the site tonight and I have yet to figure out the search feature on this site. ... I have read conflicting information about the 450BM with regard to powder burn. Some state that there is compete burn in a 16" barrel while others claim almost a 10% increase when stepping up to a 20" tube. Who is right? ...
IceAxe wrote:I believe the graph that Hoot posted shows peak pressure not propellant burned. Here is a printout that shows an idea of percent of a powders burn.
IceAxe wrote:I totally, agree with all of the above and this burn characteristic is probably more exemplified in straight walled cases. With regard to barrel length, as long as there is an unbalanced force there will be acceleration and considering that Force is equal to mass multiplied by the change of velocity over time. The magnitude (pressure) of the impulse has diminished considerably and continues to drop beyond 16 inches, coupled with the velocity the projectile is traveling at while in the last 4 inches (16-20) won't add much proportionally to the duration of that impulse or the resulting velocity, but it will add some. Personally, I am really enjoying my 20 inch barrel. However my rational for getting a 20 inch barrel was more a gas system related choice. I wanted to go with a mid length gas port to help prevent early unlocking with warmer loads yet have enough barrel remaining to provide a sufficient pulse width to cycle reliably. I also chose to go with a larger bolt and extension.
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