6mm ARC

[kmon]

I noticed that barrels for the 6mm ARC have different gas port locations. Proof & Odin barrels have rifle length + gas ports while BA & Faxon have standard gas port locations. Since Barrett used Proof barrels with + length gas ports during the development of the cartridge, there must be a reason why they went with that particular gas port location. There are members of this forum who have a lot more experience dealing with AR functionality than I do. Perhaps some of you AR gurus can enlighten me on gas port location theory for this new cartridge.

Emailed Wilson Combat. In their reply they said they didn't have any 6mm ARC components (barrels) yet but to keep checking back for new developments. My question to them about gas port location went unanswered. I figure they don't know yet themselves where it will be. I imagine they'll publicly announce when they have 6mm ARC stuff in stock.

I suspect they are using slower burning powder in the 6mmARC which yields higher pressure at the Gasport and muzzle than the Grendel. It would not surprise me if powders as slow as 6.5STAball powder can get good velocity in the ARC

Progressive powders burn the most efficient under pressure and to an extent the smaller diameter bullet/bore diameter used the less room for hot gasses to expand in and the more time slower powders can do their thing effectively. For instant you can use slower burning powders in the 243 for great results than in the 7mm-08 or 308 and you can use even faster powders to better use in a 358 Winchester than the 308 or 7mm-08. '

Another way to think of it is we start with X case volume with the bullet seated, as the bullet moves under pressure of burning powder and resulting gas the further down the barrel the more volume the powder has, now with a larger bullet that volume of the chamber increases faster as th bullet moves down the barrel resulting in a larger Expansion Chamber to hold those expanding gasses resulting in pressure dropping faster than a smaller chamber due to the smaller bullet.

With a gas gun to deal with higher pressure at the gas port you can use a smaller gas port for less gas transfer but the pressure of that gas will be the same basically between gas port sized until it hits the larger diameter gas tube and the rest of the gas system. Ot using an adjustable gas block it reduce the volume of gas getting through, or simply move the gas port further down the barrel to where the gas pressure is optimal for the system with standard port size. It is a balancing engineering game getting the gas volume and pressure correct for timing with too little, just right or too much gas.

Hope that does well enough explaining this, sometimes us engineers have trouble explaining things.