What Does this Mean?

[jackstrawIII]

Hey guys.

Took my Model 70 (308 Win) to the range to fire some of my hand loads and the cases are coming out looking unusually scuffed/marred around where the case would expand to fill the chamber. Not sure if you can tell in the attached photo, but it looks like a million little scratches all around the case. I’ve never seen cases do this before.

Any thoughts? Is that a pressure sign? The loads aren’t crazy hot though. Could there be something in the chamber causing that?

Thanks.

 

[nhyrum]

By the way the line has the abrupt edge just at the end of the web, it leads me to believe it has something to do with how the case expands under pressure. Almost like there's a lot of surface contamination in the chamber that gets impressioned on the case where it expands. I'd check the chamber with one of those small flexible cameras.

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[44 AMP]

Clean the chamber (and the ammo) and try again. See if you get the same, or different results.

My GUESS is dust/dirt in the chamber, or on the brass when fired.

 

[noylj]

Gee, looks pretty normal to me. Clean 'em and load 'em.
Maybe a bit too OCD? Maybe some residue in chamber from low pressure loads?
If concern is the cutoff from the dull "fired" surface to the shiny web surface, you could for gits and shiggles cut the case axially and see what the inside looks compared to the outside.

 

[nhyrum]

I dunno, the more I look at the piece of brass, the more it looks like it's about to separate at the case head. Could be too much headspace, which could be from pushing the shoulder back too far.

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[Aguila Blanca]

I dunno, the more I look at the piece of brass, the more it looks like it's about to separate at the case head. Could be too much headspace, which could be from pushing the shoulder back too far.

That ring at the base looks to me like the result of full-length resizing, and that's the extent of the sizing die running down on the case. So, in addition to scrubbing the chamber, I would suggest taking a close look at the die to see if there's anything in it that might be scuffing the surface of the cases.

 

[jetinteriorguy]

That ring at the base looks to me like the result of full-length resizing, and that's the extent of the sizing die running down on the case. So, in addition to scrubbing the chamber, I would suggest taking a close look at the die to see if there's anything in it that might be scuffing the surface of the cases.

This.

 

[jackstrawIII]

Several of you guys have recommended cleaning the chamber. What’s the best way to do this?

I clean the bore of my rifles with patches with o-ring jags, but these don’t do anything for the chamber.

What do you guys recommend?

Thanks.

 

[Unclenick]

There are chamber brushes with fat locking lug cleaning sections and chamber mops designed for this. You use them with regular cleaning solvents. You will find them hard to use with a cleaning rod that has a spinning handle. You want a solid handle or a T-handle rod so you can turn them in the chamber.

 

[Marco Califo]

I think you full length sizing die may need cleaning. When was the last time you cleaned it? You do not need to clean it often, but when it is dirty you need to clean it. And only size very clean brass. Take the expander ball assembly out so you can see through the die. Roll up a paper towel and insert and pull through while twisting it. If it does not come out clean, and is dark and oily, repeat. The lubricant can build up and catches dirt. Also tumble your brass in corncob so I it will shine and not look so fuzzy.

 

[Unclenick]

As a second thought, I notice the lower portion only has the markings, and if the breech end of the chamber were too wide, as can happen if cut with an off-center or dull reamer being fed too fast. You would get some extra-hard resizing effort in that area.

JackstrawIII, can you get some diameter measurments of the head below the line and just above the line and report how far above the bottom of the head those two measurements are. Also get the case body right at the shoulder.

 

[Scorch]

Looks normal to me (gunsmith for 35 years). If you want them to be shiny when they come out you will need to polish the chamber. I say just shoot it.

 

[jackstrawIII]

Unclenick, here are the case dimensions per your request:

Just above the extractor groove (below the ring of scuffing): .4670"
At the widest point (where the scuffing starts): .4715"
At the shoulder: .4570"
Distance from the bottom of the case to the start of the scuffing ring: .2520"

And everyone else, thanks for all the tips on chamber and die cleaning. Going to give those a shot and see if it helps for now.

 

[Aguila Blanca]

What is it just below the scuffing? (Say .200" from the extractor groove bevel.)

 

[jackstrawIII]

Aguila,

It measures .4700" just below the scuff line.