Odd mark on case: overpressure or irregular chamber?

[BigGoonTuna]

I recently loaded and fired a batch of .264 mag cartridges to check speed over a chronograph.  I did not have any noticeable pressure signs when firing(primers look great, no ejector marks, splits, weird recoil or muzzle blast etc).  Upon closer inspection when I got home, I noticed some odd marks right in front of the belt.  It's a small ridge that goes about halfway around the case(not a full ring), you can feel it just catch your fingernail.  I checked inside the case with a bent wire and it didn't catch on anything in the same spot.  The weird part is that it doesn't seem to have a real correlation to the powder charge, it's happened almost at random(some of the marks appeared just above starting loads, and the 3 hottest charges I fired didn't have them). 

These are new winchester cases on their first firing.  I checked them against unfired cases with a comparator and found the fired cases to be around .014" longer if memory serves me correctly(I have heard this is a common issue with belted mags, and plan to set up my sizer to headspace them on the shoulder rather than the belt once they've been fired in my rifle).  Maybe as the brass pushes back upon firing, it's flowing into the chamber where the belt goes?  Anyone had this issue before?  Am I being paranoid or is this nothing to worry about?

Photo for reference, a little hard to make out but you can see the "ridge"

[dontgetcrabs]

New to you firearm or have you shot it before?  First thought to me is head space issue?

[BigGoonTuna]

Hasn't been fired by myself much, maybe 40 rounds.  It's a 1965 model 700.

[dontgetcrabs]

I had a 25-06 that would put a slight ridge near the base after about 3 firings on the brass. Turned out it had been re-chambered by a gunwrecker that didn't have the barrel squared in the lathe.

[BigGoonTuna]

Well, I feel a little dumb now.  I went out to the workshop to take a look at some Nosler brass from factory ammo that I had fired in the gun.  None of those had any marks.  Just for the hell of it I grabbed a handful of my remaining *new* Winchester brass and examined it.  about 1 out of 5 had those same marks.  Manufacturing blemishes.  Probably the last time I'll buy that brass, not to mention I had to toss about 5 pieces out of each bag of 50 due to severe neck(folded shoulders, gouges on the case walls etc).

Appreciate the help!

[Jonathan_S]

Well, I feel a little dumb now.  I went out to the workshop to take a look at some Nosler brass from factory ammo that I had fired in the gun.  None of those had any marks.  Just for the hell of it I grabbed a handful of my remaining *new* Winchester brass and examined it.  about 1 out of 5 had those same marks.  Manufacturing blemishes.  Probably the last time I'll buy that brass, not to mention I had to toss about 5 pieces out of each bag of 50 due to severe neck(folded shoulders, gouges on the case walls etc).

Appreciate the help!

Winchester brass is garbage!

[bearpaw]

Well, I feel a little dumb now.  I went out to the workshop to take a look at some Nosler brass from factory ammo that I had fired in the gun.  None of those had any marks.  Just for the hell of it I grabbed a handful of my remaining *new* Winchester brass and examined it.  about 1 out of 5 had those same marks.  Manufacturing blemishes.  Probably the last time I'll buy that brass, not to mention I had to toss about 5 pieces out of each bag of 50 due to severe neck(folded shoulders, gouges on the case walls etc).

Appreciate the help!

interesting, good to know, nice caliber

[dontgetcrabs]