Chamber shoulder finish

[RedSkyFarm]

Hi all. Back again with a question on my recently purchased Marlin MR7 in 25-06. It has a push feed type bolt. I’ve had trouble chambering a few cases. Have one case that doesn’t chamber at all. I feel all have more resistance than normal. These have all been Full length resized. There are marks on the shoulders of the casings that start at the bottom of the neck and go the length of the shoulder to the body. If looking at the case from the mouth end, looks like a star burst pattern. The shoulder in the chamber has these same marks. These marks appear to be “high spots”. Wondering if this was due to tool chatter when it was cut. Wondering how to get rid of these “chatter” marks or if it is even what they are called. Is this what a chamber reamer is for? If so, how does one determine how much to get rid of? I’m sure you don’t want to go too deep. At the same time, don’t want it to be difficult to chamber a round. Can someone one educate me on this and what can done to fix it?
Thanks for any information.

[Scorch]

Could be tooling marks, I suppose. Sounds like dimples caused by excessive lube when resizing the brass. If it is in the steel, they can be polished out.

[RedSkyFarm]

They are not dimples from case lub. Look more like shiny scratches. Doesn’t appear until the case is chambered. Also occurs on factory ammo once they have been chambered.

[Scorch]

Then polishing the chamber may be the answer. Keep in mind that any polishing to the shoulder will increase headspace, and it would be easy to polish the wrong area in the chamber. Maybe a call to Remington Customer Service is in order. Or just shoot it as is.

[std7mag]

Is it a new rifle?
If so how long ago?
Bought used?

If new, contact the manufacturer.
If used, the to keep same barrel you'll be going the Ackley Improved route.

[T. O'Heir]

"...one case that doesn’t chamber..." That's the case, not the chamber. If it was the chamber, all cases would not fit. Not just one or even a few. Any burrs in a chamber that could cause scratches on the case will be visible.
Start by cleaning your FL sizer die. Then make sure the dies are set up correctly. The shell holder should just kiss the bottom of the die with the ram all the way up.
Check the case lengths too. Case lengths for .25-06 are the same as .30-06. Max is 2.494" -.020. That's 20 thou less. Trim to is 2.284". So any case that's between 2.484" and 2.494" is ok. Best to have 'em all the same lengths though.

[Scorch]

Max is 2.494" -.020. That's 20 thou less. Trim to is 2.284".

You may want to take a second look at that . . .
Trim length is 2.484"

[RedSkyFarm]

This is a used rifle. Although it hasn’t been shot much. Beginning to think this is why. ALL cases are difficult to chamber. Even new store bought ammo. Just had one that wouldn’t. After using a comparator, the one case that wouldn’t chamber is .0015” longer at the shoulder. Trim length is 2.484. All cases have been trimmed to 2.484. The scratches appear on ALL cases once they are chambered.

[tobnpr]

Could be a couple of issues going on.

It's possible the chamber isn't reamed deeply enough- and inadequate headspace is causing the difficulty in chambering the empty, FL sized cases.

The "shiny scratches" on the case shoulders complicate it though. You should be able to examine the chamber without needing a borescope by simply removing the action from the stock, and shining a small light down into the chamber. Could be scratches from swarf getting under the reamer flute(s)- or it could simply be debris that's gotten into the chamber. Have you patched it out/cleaned it thoroughly? Take a Q-tip and run it inside and around the shoulder area, see if any fibers get grabbed.

I would first determine if there are any raised burrs or debris in the shoulder area- and if cases are still hard to chamber (I would use a go gauge, but a FL sized case with a fully bumped shoulder will work)- using a stripped bolt so you can feel what's going on- then most likely the chamber is short. Simple enough to deepen the chamber a bit (don't even have to pull the barrel) to get headspace where it needs to be, and it'll at least partially clean up the shoulder in the process.

[RC20]

Well clearly there is a chamber issue.

As I have told them at work more than one time, do you want me to figure out what the problem is or do you want me to fix it (hint, engineers charge about 15k and then tell you what it might be!)

One work around is to take new or fired brass and push the shoulder back further than normal. Fired would tell you what the starting lentch should be but so will pulling a bullet out of factory round as they are a chambering problem

note: This does not fix the imprints and it will almost for sure imprint when fired (picture would be good)

Gun Smith: find one who knows what he is doing, polish the chamber or if he is capable, you could have a few more thousandth head space created (not sure how fine a control a local shop would have). That would also take care of the need to polish.

You could just have it polished, then back to the first method, pull bullets or get new brass and set back more than normal from there the minimum of .003 or so.

note: It does happen, we had a Sig that had marks and extraction issues, bad chamber work.

[tobnpr]

Need a picture of these "scratches"- and of the chamber shoulder.
There may certainly be a chamber defect, but I'm not convinced the hard chambering- and inability to chamber the one slightly longer round of factory ammo (which was still likely SAAMI spec) is not due to a short chamber.

[Unclenick]

There is need for a headspace gauge first, to see if the chamber is short. If it is, it can be final cut with a finishing reamer or it may be possible to sacrifice a couple of fired cases as laps for the shoulder. You can special-order 25-06 Flex-Hones for the final surface finish from Midway or factory direct, but I don't think these will cut enough to take a chatter ridge out.

[RedSkyFarm]

I believe and sounds like a couple of you believe the chamber may be short. I’ll see if I can find a head space gauge to verify. I have taken pictures but need to learn how to get them posted here. I’ve attempted to contact a local gunsmith but as of yet haven’t been able to talk to him. How much head space would be considered acceptable? How much is too much and what would be the minimum? Thanks.

[tobnpr]

^^^
Here's the thing...
If you have a chamber burr, or some sort of foreign matter in the chamber shoulder, it will prevent a case- or a go gauge, from seating fully on the datum- that's why you need to rule out that whatever is marking up your brass isn't preventing the round from seating before you check chamber depth/headspace.

At that point, it matters little whether you're using a properly FL sized case, or a hardened precision gauge- both should chamber. I've seen chambers scratched up by swarf that left ugly marks on the brass but didn't affect chambering, or extraction. If there's no raised burr(s) or debris preventing the rounds from seating, it IS a short chamber (or perhaps a different bolt given it's a used rifle). Either way the chamber would need to be deepened.