100% agreement with
@GrandpaDeadLegs ... I've found that a longer than standard gas system is nearly a necessity for barrels longer than 20-22" depending on cartridge. The more prefer you burn the higher the pressure; the heavier bullet, generally, the slower the powder. Combine those in a long barrel heavy bullet rifle (224v, 6.5CM AR10 etc, for example) and more gas exists longer in the barrel. Enter dwell time tuning....
The rifle length gas system is 12". So a typical 18" barrel has 6" of "dwell time" (not the correct way to quantify it but it doesn't require the math and easier to understand in terms of inches). If you go to a 22" barrel, there is now 10" of "dwell time" which is a ~66% increase in dwell time>. This can be very detrimental to brass and precision because bolt carrier group tries to start unlocking at about the same time as the 18" barrel but bullet still has to travel another 6" before exiting muzzle. This is bad.
If you add length to gas system you can keep the approximate dwell time similar and reduce early unlocking but, longer barrels can be a $@$&+ to tune. One click is too much gas two clicks is too little and then you need to tune buffer and spring.
In a perfect world, we would find the optimal gas system lengths for 20, 22, 24 and 26" barrels to make them easy to tune and more reliable but until the Valkyrie, a 24" barrel 223 was a bit uncommon and more of a novelty. The 224V was designed around a 22-24" barrel, so we may start seeing new gas lengths to maximize precision/reliability.
