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AR15.COM
12/9/2016 11:55:02 AM EDT
Would a 308 Win fired in a 26" barrel burn the powder more consistently then say a 308 Win fired in a 20" barrel? Would the longer barrel have a better SD & ES?
12/9/2016 12:01:26 PM EDT
[#1]
Interesting Question.

I don't believe that barrel length has an effect on powder burn consistency.  I've had great loads come out of both long and short barrels as far as ES/SD.  
12/10/2016 11:53:43 AM EDT
[#2]
Quoted:
Would a 308 Win fired in a 26" barrel burn the powder more consistently then say a 308 Win fired in a 20" barrel? Would the longer barrel have a better SD & ES?
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All of the stuff that's really going to affect SD/ES of velocities takes place before the bullet is fully engaged into the rifling.
12/10/2016 1:13:19 PM EDT
[#3]
Some powders burn hotter than others. That's why folks test with different powders for best performance. Quickload software can give you a good estimate how much powder is burned with a given powder from what I have been told. On my wish list of things to buy in the future.
12/10/2016 2:21:56 PM EDT
[#4]
Quoted:
Would a 308 Win fired in a 26" barrel burn the powder more consistently then say a 308 Win fired in a 20" barrel? Would the longer barrel have a better SD & ES?
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The bullet reaches Mach by about 3" into the bore.
The bullet reaches 90% of MV by about 12" into the bore.

On the other hand, given a well chosen slower burning powder, one can get another 100 fps from a 24" barrel than from a 20" barrel, and that 100 fps translates into another 100 yards downrange befor Mach transition.