Rifle Chamber Questions

I have a question about something it appears that I'm seeing with fired brass in a rifle I've had issues with. Earlier this year I had another lengthy thread going on it, and I'm kind of picking up where I left off, with more information.
It's a rifle I've had to bump shoulders .008-.009 to chamber brass. I've reduced that somewhat by changing headspace gauge, and getting a pair of quality Starrett calipers, but I'm still having to bump 5-6 thou. I don't believe I'm actually pushing my shoulders back that far. What I have evidence of, and it seems impossible is high and low spots in my neck and shoulder. Almost like ripples or ridges running with the shoulder and neck of the brass all the way around it. If what I'm seeing is actually what's going on with my chamber, it seems impossible for a reamer to cut a chamber that's not perfectly round and ripples in the steel. Has anyone ever heard of something like this, or know of any possibility or circumstances that can produce something like this. I can go into more detail on how I believe this is what's happening, if you guys want.
A little more info that make it seem more impossible. I had all but given up on this barrel and pulled it off and threw it into a closet from now on. I started load development with copper solids of various weights and profiles, and it would not shoot any of them at all. Worst shooting rifle I ever had. As a last ditch effort before I completely pulled the plug on it, I decided to load some test rounds with a different bullet, and powders. Here's the mind blowing part. Over a 6grain powder spread, It put 14 shots in .5 grain increments with 250 gr Berger EH into a group that was probably less than 3/4" outside to outside. I didn't measure it, but I'm pretty sure it was not 3/4 outside to outside. Definitely not more than that, with 0 load development. Just pressure testing and seeing what those Bergers would do jumped .120
I don't know what to make of it, and still not convinced I'm out of the woods on it yet with what I'm seeing going on with the brass. These were all 3 and 4 times previously fired brass. To say I'm confused is putting it mildly, but what it did with the 250 Bergers was nothing short of impressive.
I feel like I still need help wrapping my mind around how any of this can be possible, or help understanding other things that could possibly be going on here, if what I'm seeing is caused by something other than a screwed up chamber.
Thanks!

Can you provide a picture of what the brass looks like, is it after firing or after sizing? If sizing, you have too much lube. At .75 MOA, that is pretty good for a big Magnum for hunting.

I second the too much lube theory. If you're using minimal lube and it's still doing it you probably have to clean your dies.

As far as the 250gr Berger's I would reload the same test and shoot it at 300. I was fire forming my 300wsm brass with some random magnum powder and random projectiles and it was clover leafing at 100. Thought holy crap that was easy. Loaded up 10 just like them and shot them at 300 and groups went to crap. Really bad. I always test at distance and multiple times to confirm I did indeed find the magic load

What cartridge?

Dies being used?

I have seen many chamber jobs with imperfections, such as, grooves from embedded chips, steps and even double cut chambers. Most common is chips causing grooves, but also damage from a reamer hitting the top of the chamber with the barrel stationary, you could see the flute gaps in the marks left behind. This was not as rare as I would have thought. Very rare were pilots that had broken, but it happens and leaves telltale signs behind. Have seen shoulders that were convoluted, unsure of the cause.
However, none of these things are common, I worked in warranty for several rifle brands, mistakes happen on production rifles. Even my own high end 22-250 has an eccentrically cut chamber, .008" off bore centreline, it still shoots ok, so when it's shot out, a new barrel will be even better.

If a chamber is long, you size the brass to suit, problem is gone. If your chamber is short, most of mine are, you need to use a modified shell holder, you take .010" off the top and adjust your die as you normally would to get .002"-.0015" bump…

Cheers.

Can you take a fired case and chamber it?

So what I'm talking about you can't see by eye, but out of the chamber I can't put the neck on a concentricity gauge and the neck has waves in it all the way around it. The gauge moves .002. The first pic is a sized case when I put a .420 gauge on the shoulder it's only contacting the shoulder intermittently. Fired brass before sizing does the same thing. You can see where the sharp edge of the headspace gauge contacts the shoulder intermittently. I'm struggling with lighting to get a pic that you can actually see it, but a circled a pic where you can see 2 of the marks. It does this after firing and before sizing. The more I size the more those are visible and a little bit longer.
As far as lube goes, I'm using a light mist of Hornady one shot. Also have cleaned my dies repeatedly

ShtrRdy said:

Can you take a fired case and chamber it?

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No. I have to bump.006 to chamber it.

MagnumManiac said:

If a chamber is long, you size the brass to suit, problem is gone. If your chamber is short, most of mine are, you need to use a modified shell holder, you take .010" off the top and adjust your die as you normally would to get .002"-.0015" bump…

Click to expand...

My chamber is short. Won't close on a go gauge. I'm using a Forster coax press, so it doesn't use a shell holder. It's integrated. I have the attachment to use a shell holder, but then it sets the case too high up and I can't back my die out enough.

FireFlyFishing said:

What cartridge?

Dies being used?

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338 Sherman Mega. Using Hornady Match bushing dies

Chesterrose79 said:

As far as the 250gr Berger's I would reload the same test and shoot it at 300. I was fire forming my 300wsm brass with some random magnum powder and random projectiles and it was clover leafing at 100. Thought holy crap that was easy. Loaded up 10 just like them and shot them at 300 and groups went to crap. Really bad. I always test at distance and multiple times to confirm I did indeed find the magic load

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That is the plan. I've not done any load development yet. I'm just pressure testing in .5 gr increments. Once I start load development, I'll shoot at 400. Then test farther out when I think I've found a good load

Chesterrose79 said:

I second the too much lube theory. If you're using minimal lube and it's still doing it you probably have to clean your dies.

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Using a light misting of Hornady one shot, and I've cleaned my dies after each time I use it. Not sure how I can get less lube on it