Seemed bore fluctuation at gas port

[JaredBT]

Hello all Im breaking in a barrel, Im feeling what seems like a fluctuation in the rifling / bore diameter at the gas port hole area of my 308 20" bore... While running a patch down the bore, when I get to the gas port the pressure (resistance pushing the rod) lessens at the port area then picks up again just past it. Visually I cant see anything wierd. Any thoughts?
 

Thanks.

[shepp]

Welcome to the forum feel free to tell use about yourself in the intro section

 

[jtallen83]

Welcome from Iowa, via Pensacola!

What does it feel like going from chamber to muzzle? How many rounds? Possible they put extra effort into lapping the area at the gas port, just a wild guess on my part though.

[planeflyer21]

Interesting.  I have the same sort of bore variation with a Ruger MKIII pistol.  Cleaning from the breach end, there is an area about 7/8" long ending at the muzzle that is noticeably "looser" than the preceeding bore.

My theory is that this particular barrel was clamped super-mongo hard when being bored and then, when the clamping force was loosened, it allowed some spring force in the steel to open up a couple of thousandths or so of an inch.  I've seen this happen with non-barrel lathe work.

That being said, what type brand of rifle is this we're talking about?  Did you purchase/acquire this rifle new?  Is the outside of the barrel bulged?

I've seen .30-30 rifles and handguns "ring" the barrel, when they were fired with a barrel obstruction, the ring appearing just behind where there obstruction had been.

[survivalshop]

8 hours ago, JaredBT said:

Hello all Im breaking in a barrel, Im feeling what seems like a fluctuation in the rifling / bore diameter at the gas port hole area of my 308 20" bore... While running a patch down the bore, when I get to the gas port the pressure (resistance pushing the rod) lessens at the port area then picks up again just past it. Visually I cant see anything wierd. Any thoughts?
 

Thanks.

Contact the Barrel / Rifle manufacturer , If possible , if not , have it checked by ADCO or some other Barrel maker/repair or replace the barrel . Hard to say whats up , but the explanations above sound possible . 

Edited February 27, 2017 by survivalshop