I have been checking out the new Battle Arms Development 10.5" barrel. A unique spec I noticed is that it has a pistol length gas system. Most 10.3/10.5" barrels run a carbine length gas system in 5.56/.223.
The positives I can think of areThe shorter gas system will provide a longer dwell time cycle the gun a bit slower. Negative it will have greater felt recoil. Also the 10" barrel and car length gas system is proven to function reliably, is there an issue that BAD is addressing with the pistol gas?
The time it takes the bullet to travel from the gas port has little to do with it all because the time difference for the bullet to travel an extra few inches in minuscule and the bullet is out of the barrel before the gas can pressurize the system. What matters is how long it takes the bore to vent the pressure. It takes time for the pressure to drop after the bullet exit the muzzle and it’s this residual pressure that operates the action. Using two gas systems of the same length from chamber to port, the longer the barrel, the more time it will take to vent the gas and the longer the bore will be at a pressure that will operate the action. Which should be a good thing. However, there is such a thing as too much of a good thing.
When the carrier starts moving, the carrier key separates from the gas tube and gas stops flowing into the expansion chamber. But it does not stop flowing out of the gas tube. With the longer blow down time, more gas flows from the gas tube, into the action and out to the shooter’s face. It’s also blowing out of the chamber end of the bore. By itself, it’s probably not enough of a difference that most shooters would notice (unless a suppressor is added to the mix) but that is the trade off.
The pistol gas system will take longer for the pressure drop to atmospheric to reach the port from the muzzle, but where the gas is tapped will be higher and the whole system will have less forgiving
The carbine gas system will take less time to blow down but the gas pressure will be lower at the port and easier to manage
It doesn’t look like a pistol length gas system to me. It looks like a carbine length gas system and Lancer carbine length carbon fiber handguard. Pistol length gas systems are 3" shorter than carbine. Here is a sketch of a 10.5" barrel with a carbine length gas system and profile similar to BAD’s.
