6.5 Grendel barrel Length?????

[lazyengineer]

Powder conversion with most of the propellants we use in 6.5 Grendel is almost 100% complete within the first 1.5-3" usually, depending on the propellant/projectile combo.

"Unburnt" gets confused with "mostly-converted" powder that has already been burned and released its potential energy within the first few inches of the chamber, but leaves tiny residual particulates that are still very hot. We also get soot residue inside the spent case, which reloaders are generally familiar with.

If considerable unburnt powder was making it to the gas port, imagine what would be happening in your gas system.
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Respectfully, I've seen numerous people say this, and I don't think this is true. And neither does QuickLoad
https://www.usreloadingsupply.com/news-quickload-review

QuickLOAD also gives you a lot more perspective concerning the trajectory of your projectile, FPS, amount of powder burned and what percentage of powder should be burned within the barrel. Have you ever shot a round and then see unburned powder coming out of your barrel? Well, this software can tell you within a fair margin of accuracy if a load should burn all of the powder or if some (or a lot) will be left unburnt.

Nor does the American Chemical Society
https://www.borlik.org/wp-content/upload...Bullet.pdf
They aren't detecting soot in residue from handgun discharges in these analysis - they are detecting nitrates. That's gunpowder.

Nor does the premise really make any logical sense, since why bother tuning burn-speed, if it's all burned in the first 3" anyway? I would just be reloading with the "slowest" gunpowder I could physically stuff into the case, if that were so.

As to still-burning kernels entering the gas system, I do agree relatively little mass of powder is left by that point. But I do think that indeed there is some potentially still burning powder entering the gas system. I don't think that's a problem at all: it's rated for heat and pressure, and the port remains open to the barrel (i.e. it cannot exceed the pressure of the barrel).