Re: Best powder for short barreled 308
"So please explain how a slower burning powder "Varget, will produce better velocity in a 16.5 inch barrel than say 4895 or 3031. Both are faster burning powders."
.Ara, I make no prediction on what powder will be ideal for your rig.
I know what I said is counter intuitive but intuitive in this case is based on incorrect "conventional wisdom". I've already explained that the powder which produces the highest speed in a 24" barrel will do so in your 16" barrel; the bullet's acceleration is solely dependent on the time:pressure curve, it matters not at what part of that curve the bullet exits, fastest in one length will be will be fastest in the other. That's all there is to it. I won't argue with your author but I will question him on this point. I'm sure Mr. Rinker is a smart and quite knowledgable man and I would love to have his book for study but he is not the first author to write something which sounds right but isn't entirely correct in application.
Think of how little heat energy can possibly be transfered to a bore surface in the 2-3 milliseconds it has to do so. Certainly heat (energy) IS transferred or the barrel wouldn't get hot but that's because the burn temp is quite high, hot enough to melt the steel if it were maintained longer. IF barrel temp mattered very much we could reasonably expect the last round fired would always be fastest but...not really! Thus, Mr. Rinker's equating a measurable velocity difference based on heat exchange to the barrel because of powder burn rate is quite a stretch of both physics and logic! The actual bore time of bullets at say 2,500 fps and 2,800 fps isn't much no matter what powder is used so the end difference in energy transfer will be infintesmal no matter the burn rate.
We reloaders make a lot of noise about "fast" and "slow" powders because it matters to us but the real world time differences are quite tiny. We're only moving the instance of peak pressure small fractions of a millisecond and changing the duration of that pressure peak just a little longer.
Last edited by boomtube; 04-20-2013 at 10:04 AM.