Gunsmithing Brass issue

[Covertnoob5]

Hey all, just wanted to get your opinions on something Weird going on with my brass. Every firing no matter the charge weight I get this line that looks like a cut about 1/4 of the way around the diameter of the brass. Pics below is 39gr H4350.

I was doing load dev on a basically new barrel. 50 rounds prior to doing an initial load ladder to shoot a local match.
Load & barrel specs are
6.5x47 lapua 26”
.167FB
.295 nk
Virgin lapua brass
Rem 7 1/2BR primers
135 A-Tips
Started at 39gr h4350 seated 10 thou off
Went up to 41 gr in .2 increments

Brass growth between unfired virgin and 1x fired is only about .006” so I don’t believe it to be a headspace issue (?), but the line seems close to a headcase separation issue. I just don’t know how that could be.

Any thoughts and opinions would be welcome! Thanks!

 

[Steel head]

Looks like the unsupported area of the case at end of barrel with a chamfer.


Cases typically separate at least another 1/8-3/16 up the case.

 

[ArTeeKay]

Hard to tell from the picture, but is there a machining defect in the case head area of your chamber?

 

[Covertnoob5]

Hard to tell from the picture, but is there a machining defect in the case head area of your chamber?

I don’t have a borescope but I did my best with a flashlight and my mk1 eyeball lol and didn’t see anything obvious.

 

[Covertnoob5]

Looks like the unsupported area of the case at end of barrel with a chamfer.


Cases typically separate at least another 1/8-3/16 up the case.

Thanks. That what I was thinking too, but just found it weird. I’ve called the smith already and he said to send the barrel back so he could look at it.

 

[Covertnoob5]

Also wanted to ask you guys if you all think I should toss the brass or can I keep shooting it? I hate to toss lapua brass after 1 firing. Especially in today’s climate of unavailability.

 

[ArTeeKay]

It may not be visible to the eye. Do you have a fine pointed tool that you can drag through the chamber? If it's making visible marks on your brass, it may be large enough to feel, even if you can't see it.

Just saw you're sending it back to the smith. I'm curious what the cause is, updates are welcome.

So long as the brass shows no undue stretching, I think you're ok. Especially if you're only going to be neck sizing rather than full length sizing your cases. Your calipers are your friend here. I'd save it, and if you're worried, don't load it again til you hear back from your gunsmith.

 

[Covertnoob5]

It may not be visible to the eye. Do you have a fine pointed tool that you can drag through the chamber? If it's making visible marks on your brass, it may be large enough to feel, even if you can't see it.

Just saw you're sending it back to the smith. I'm curious what the cause is, updates are welcome.

I can look for a fine pointed tool. Another thing that was weird to me is that it’s only happening after the brass is fired. When I chambered a round, then ejected it without firing, the brass was normal.

 

[Steel head]

That’s in the stoutest area of brass, I’d 95% keep shooting that brass from what the kinda bad picture shows

 

[Covertnoob5]

That’s in the stoutest area of brass, I’d 95% keep shooting that brass from what the kinda bad picture shows

Sorry I can try to get some better pics.

 

[ArTeeKay]

A dental pick would be my choice.

As for not showing the line on chambering, if it's a defect too small to see, it's not going to show up on brass until that brass is subjected to firing pressure.

 

[Covertnoob5]

Updated OP with hopefully better pics @Steel head

 

[Covertnoob5]

A dental pick would be my choice.

As for not showing the line on chambering, if it's a defect too small to see, it's not going to show up on brass until that brass is subjected to firing pressure.

I’ve got a dental pick. Thanks for the suggestion

 

[hic28]

This better not be your excuse to not shoot tomorrow lol.

is it only on a 1/4 of the base? If you are coming tomorrow, bring the rifle and brass and I’ll take a look

 

[Steel head]

Looks like smith left a burr when cutting the chamfer.
Brass is probably GTG.

 

[Covertnoob5]

This better not be your excuse to not shoot tomorrow lol.

is it only on a 1/4 of the base? If you are coming tomorrow, bring the rifle and brass and I’ll take a look

Haha I’ll be there tomorrow no worries. But yes it’s only about 1/4 the way around the base. Not all the way around.

 

[ArTeeKay]

I second steel head's assessment. You're fine. If the smith wants to clean up his work, I'd let him. Just for kicks.

 

[Covertnoob5]

I second steel head's assessment. You're fine. If the smith wants to clean up his work, I'd let him. Just for kicks.

Yea he offered right away after he saw the picture.

 

[FuhQ]

Hard to tell from the picture, but is there a machining defect in the case head area of your chamber?

Looks like he had a poorly finished or worn-out reamer...Or a shaving or chip got in there and wreaked some havoc while finish-cutting the chamber. It doesn't look too deep on the case (but I haven't seen pics of the chamber, so just guessing), but probably just needs a good chamber polishing to correct it.

 

[2aBaC̶a̶]

That’s in the stoutest area of brass, I’d 95% keep shooting that brass from what the kinda bad picture shows

Only 95%?

I imagine its normal to chamfer the leading edge of the chamber. Maybe he missed this step.

I would 105% keep shooting it.

 

[iceng]

If that's from the first firing, you should be fine to reuse it. As others said it's a chamfer on the edge of the chamber. Your Smith can fix that easy, just probably had a brain fart and didn't do it originally.

Also someone suggested a pick to feel inside the case. Unfolded paperclip works well. If in REAL doubt, send a piece or 3 back with the rifle to have the Smith check it inside with a bore scope, or if all else fails, cut a piece in half and have a real good look.

You should be good to go, but get a second opinion (ie: your Smith)

 

[sirhrmechanic]

Looks like smith left a burr when cutting the chamfer.
Brass is probably GTG.

May also be a ridge at the spot where the chamber flares out and the brass is unsupported. That chamfer or flare is cut after the chamber. And in cutting the chamber, there can be a tiny bit of surface hardening caused where the tool cuts out metal. Then When you cut a chamfer, that hard surface translates into a tiny ridge as the tool doesn’t cut the hard area as deeply as the softer metal under the surface.

the brass looks fine, and if things are not hanging up, chamber is probably fine. Those little ridges in the throat can usually be removed with small round fine polishing stones and a bit of kerosene as lubricant. They would lap/ polish out easily.

likely, as pointed out above, you could detect with a small probe that you drag out if the chamber. You don’t need pressure! Don’t scratch the chamber by aggressively using a dental pick. But with a sharp point and very light action dragging it, you may find a tiny ridge right where the chamfer begins at the back of the chamber.

I have a diagram of this somewhere that I used to show one of my guys who was learning to work on hardened kingpin bushings. It’s a simple sketch so explains the cause... let me know if you want me to dig it out. Once you see what’s happening, correcting is child’s play.

Sirhr