I helped a friend chamber a rifle last year, and he recently showed me some interesting witness marks in the fired brass. The puzzling thing, as you can see in the photos below, is that this feature does not extend around the entire perimeter. It takes up about an arc about a third of the way around.

At first I thought it was a groove from a chip lodged in the reamer, but it appears like more of a step down, where the diameter forward of the mark, (the short section towards the shoulder) is slightly smaller than the area immediately aft. But again, only through an arc of approx. 120 degrees. He also reports extraction is stiff.

Thoughts on the cause? After sleeping on it I have a theory... FYI, we rough cut the chamber with drill bits on a small lathe, but did the finish reaming by hand because the lathe is small, and that's the way I had done it before even getting a lathe.

Ideas for cleaning it up? Thoughts on safety of reloaded brass? Thanks.

Yep set it back and recut. WhileI guess you could cut an AI you still should set it back. You can try polishing the chamber so the edges aren't as sharp.

Other than looks shouldn't be an issue for reloading.

I'd guess that you were driving the reamer to lightly and some metal welded to the leading edge of one flute, built up, cut a partial ring and them broke free of the flute. It looks like a bad one and would probably account for the hard extraction. It's hard to say without seeing numbers but it may be a bit to much to just polish out.

You can mic the area over the ring and then mic the area on either side to figure out how deep it is. It looks sort of like a 30-06. In which case your body taper per side would be about .006 inch per inch per side. If the ring is .002 inch deep you would have to set the barrel back 1/3rd of an inch to clean it up.

Thanks guys. I was hoping to not have to set it back because we installed sights which we'd have to time just right, but I agree that's the best way to fix it. Do you think this could also affect accuracy?

Your analysis of the cause is spot on, and you violated Rule #3 of chambering; never use an unpiloted rougher/drill too deep, and never allow the finisher to float without pilot engagement, because it won't clean up. That is what happened.
How badly does it bother you? Polish it a bit and the extraction should ease up. Is accuracy affected? Not if the front part with the bullet, is concentric with the bore. As it should be.
Now, if this is for a paying customer, then you owe him a new barrel.
Rules one and two? Those are for another lesson.

DPCD, I think you nailed it... That was my theory alright, but hadn't really expounded on it with any written analysis.

Does it bother me? Not a bit! It bothers my friend though... He's not a paying customer, I'm just a hobbiest. In fact I supplied the $20 gun show barrel to help him build a shooter so we could hunt together so neither of us is out much at this point. I saw it as a good opportunity to help a friend and try my hand at my first threading and chambering job with my 9x20 Jet lathe. I won't try that again with this lathe!

We will have to hash out together how much more effort and money we want to put into this particular project. I think I've learned my lesson here on #3, thanks again!

P.S. Please though, rules #1 and 2???!!! Don't leave me hanging like that.

Maybe I missed it, what chambering/caliber?

30.06

I see two distinctive edges on that step. Leading edge and trailing edge. Veddy peculiar in a step, dontchaknow !



chamber ring by Rod Henrickson, on Flickr


chamber ring2 by Rod Henrickson, on Flickr

Your crimping grove tool slipped !

quote:

Originally posted by mete:
Your crimping grove tool slipped !

Probably had so much powder in it, that the case stretched so bad that the original cannelure ended up there.

If it's a recessed groove in the brass then it has to be a raised groove in the chamber. A reamer should take it out.

No, he has a whopper jawed (technical term) chamber; he already finished the chamber; hence the good front part and the back part that is not concentric with the front. There is no fix for it short of setting it back. Or living with it.

quote:

Originally posted by clowdis:
A reamer should take it out.

But a reamer didn't take it out the first time...

I believe that groove is in the chamber. The brass extruded into it.

""whopper jawed"""
Darn haven't heard that one since my grandpa died.

Two different diameters.

One is offset, made by the edge of the drill bit: And a little of the 118 degree left by the tip of the bit is there. It is the groove pointed out by spearchucker. The smaller diameter made by the reamer is to the right of the "bulge"

The diameter to the right of the groove was the final made by the reamer.

What we have here is the final drill bit for roughing was both too large in diameter and not on center. Then the piloted reamer was ran in but did not straighten out the roughing area

I betcha if you could measure the "bulge" you would have a 118 degree (or 135 degree if a 135 degree drill was used) slope on the right side.

Think about it. DPCD is right on.

I do not use drills as roughers. If I plan on cutting many chambers with a reamer I buy a rougher reamer.

Run a bore scope in the chamber and you should be able to see the portion of a groove left by the rougher drill.

quote:

Originally posted by ramrod340:
I believe that groove is in the chamber. The brass extruded into it.

""whopper jawed"""
Darn haven't heard that one since my grandpa died.

Way down in the swamps of Georgia where I was hatched the proper term is "Whompy Joe'd".

And I know where that term came from!

It's pretty hard to determine what caused it with just photos some times. In this case, it looks like a ring to some and a step to others. It could be either. The only way to tell for sure is simple, hard measurements. If it's a ring as in figure #1, B will be greater than the A and C measurement. If it is a step there will be no high B point and it will be a simple step like in figure #2.

If it is a simple step then there is no reason to do anything. It won't hurt brass life and everything will work fine.

If it's a ring, then there will be a problem as the ring area will anchor into the chamber and he will have to yank or bang on the bolt handle to pull it back.

In either case there is no simple fix. The taper per inch is about .015 inch per inch. Or .0075 per inch per side. The step or ring can be measured, the difference taken and from that it's very simple to figure out how far the chamber will have to be set back. Like I say though. If it's just a step I would leave it alone. It's just sitting there smiling and not hurting anyone. Let it grin and be happy.


chamber ring 3 by Rod Henrickson, on Flickr

Yep, mystery solved...

I was being conservative in my selection of drill bit diameters and depth, but I failed to account for the likelihood of being off center. I'm not a machinist, and was using a cheap Chinese made 9x20 hobby lathe. I have a spindle spider on the backside of the headstock and had it dialed in as close as I could manage, but apparently it wasn't enough. Either that or the barrel itself was off enough to affect things...

Anyhow, good lesson learned on an inexpensive $20 gunshow barrel. Thanks again gentlemen!

Rod, good stuff in your last post. I was typing my other one before I saw it...

I have not taken measurements, but visually this feature is a step. My first thought was that it was extra material in the chamber, creating an indentation in the case. (the inverse of feature "B" in diagram #1 above) The hard extraction was then this extra chamber material "sizing" the forward part of the brass as the bolt was pulled rearward. However, given my chambering technique and with the concurrence of several others I firmly believe it was an off-center roughing bit that caused this.

There's also really no explanation for how a ring could form otherwise. Given the full rotations we were putting on the reamer any chip out of one of the cutting flutes would be cancelled out by the cutter following it. And if they were uniformly damaged, well then this feature would occur all the way around the circumference.

quote:

Way down in the swamps of Georgia where I was hatched the proper term is "Whompy Joe'd".

Yep but I'm from MO our toes did dry out.

I have made rings just like that using only a finishing reamer. I haven't used roughers in years. It's caused by a piece of material temporarily welding to the flute for just a millisecond and then breaking free. Or you picked up a chip when you inserted the reamer and made the ring before it cut through it. Like I said, you won't be able to tell until you measure the fired case. Without having a case in my hands it's hard to tell. If it's a step it will be smaller in the front and bigger in the back so you won't have any extraction problems.

But, determining the cause does not matter much if you only cut a few chambers. The odds of it happening again are slim.

It is and was caused, exactly as I described, and is portrayed by Rod's picture #2.
I have plenty of $20 barrels in 30-06 should you want to try again.

quote:

Originally posted by dpcd:
It is and was caused, exactly as I described, and is portrayed by Rod's picture #2.
I have plenty of $20 barrels in 30-06 should you want to try again.

And the best part is that neither one of us is close enough to go take a look at it to say for sure. It will be, forever a mystery. Just like the Caramilk secret and it will annoy me for at least - - - - - - - - - 13.2 seconds ! Cause, it ain'tent my gun. And I dint doodeded it! LOL

I think I'm going to call this new feature a "non-circumferential micro-shoulder" and market it as an improved wildcat based off the 30.06.

Forgive me if it's been mentioned (and I have missed it) but could the problem be fixed by rechambering to a conventional improved version?

quote:

rechambering to a conventional improved version

Yes he could as I mentioned. Probably not clearly. However, to properly do a rechamber to an AI you need to set the barrel back. So if you are setting it back why not leave it as a 30-06. Saves you forming brass and new dies. For a $20 I'd either shoot it as is or make a tomato stake out of it.

Funny how we perceive things sometime. If it's like the #2 picture (and it probably is) then the barrel will need to be set back to correct it. If you're reloading then it ought to be corrected but if you're shooting factory ammo then let it slide. How about some eye puzzles for all the internet gunsmiths?