Gas System Length

[gr8horses2003]

This is a question asked on another forum. I am building a LR upper in .260 imp 30 and would like to know the answers to these questions.

He says:

I have a 26 inch barrel with a rifle length gas system. I have another rifle with 26 inch barrel with gas port moved out 2 inches.

My question is, the affects on the bullet with a rifle length versus a 2 in longer gas system:

(1) will the bolt unlock a little sooner with a rifle length gas sysem or is it about the same with an extended gas system that's only 2 inches longer? Does the extra gas system length make any practical difference?

(2) Is the bullet in the bore with the rifle length gas system on a long barrel, when the BCG starts to unlock sooner with the shorter gas system? Corollary: What is the optimum length barrel, remembering that dwell time varies with the powder burn rate and charge, and that the bullet needs to be out of the barrel before the gas pressure decreases. Is there some rule of thumb for the length of barrel that can be beyond the gas port?

Thanks for the help.

Harry

[dauntedfuture]

The longer the gas system, the longer it will take for the system to start unlocking. Pressure will be maintained in an ever decreasing rate in the gas system until the projectile exits the barrel as available space for gas increases. The longer the gas system the lower pressure the system will operate at. A smaller gas port or adjustable gas block will adjust the volume of gas, not the pressure.

There is a point at which getting the gas port too close to the muzzle makes things not work as there is not enough dwell in the system to make things work.

On a hot rod like the .260 I would think longer is better, that's one hot rod ctg. and you are going to be dealing with lots of gas in that .308 designed system. I should think that who ever made the barrels has made the systems work with a longer system and or a smaller gas port. I believe DPMS now has a 6.5 creedmore upper so they made it work but that .260 improved has more powder in that case and your using slow powders to make it sing.

When David Tubb started experimenting with a .260 in a AR-25 years ago he had all kinds of issues and blew up at least one rifle. Soon there after he went to the t2K, a bolt gun.

[gr8horses2003]

Thanks for yor reply. I am thinking that the longer gas system is good thing on a long barrel rifle.

Harry