Case mouth ring separation

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wildfowler
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Re: Case mouth ring separation

Post by wildfowler »

dellet wrote: Tue Apr 16, 2019 12:27 am Have you tried to chamber an empty case?

I would be inclined to try a couple things. If an empty case will not chamber, I would trim maybe .005” and try again until the bolt closes. A stripped bolt would be best. This will give an idea of how much brass is in there.

If it closes on an empty, then you know it’s farther forward and hanging up on the bulllet. Then I would compare the length the bullet used to hit the lands at and how much shorter it is now.

With that information it might change my next step, that may or may not be suitable to print on an open forum :shock:
Do you think there is any chance the case mouth could “crimp” closed slightly rather than stopping forward bolt movement? False reading?

Maybe pay attention to the diameter of the case mouth before and after.
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dellet
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Re: Case mouth ring separation

Post by dellet »

wildfowler wrote: Tue Apr 16, 2019 4:39 pm
dellet wrote: Tue Apr 16, 2019 12:27 am Have you tried to chamber an empty case?

I would be inclined to try a couple things. If an empty case will not chamber, I would trim maybe .005” and try again until the bolt closes. A stripped bolt would be best. This will give an idea of how much brass is in there.

If it closes on an empty, then you know it’s farther forward and hanging up on the bulllet. Then I would compare the length the bullet used to hit the lands at and how much shorter it is now.

With that information it might change my next step, that may or may not be suitable to print on an open forum :shock:
Do you think there is any chance the case mouth could “crimp” closed slightly rather than stopping forward bolt movement? False reading?

Maybe pay attention to the diameter of the case mouth before and after.
I am actually kind of hoping for something like that, and he should be able to measure for that.

It's possible forcing a case with a tapered neck into the existing stuck ring, might be able to pull it out. You might be able to size an uncut 223 case and use it, since it would have a taper.

The redneck in me says find out how short of neck you can chamber, make a low end round up with a .015" shorter neck and blow it out :roll:

If the full length case chambers, its got something farther down the barrel and I'd be less likely to say hold my beer.... :mrgreen:
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Sig220
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Re: Case mouth ring separation

Post by Sig220 »

I read through this thread twice, didn't see where you tried this:

Put a cleaning rod in from the muzzle end and then attach a larger then bore brush, pull the brush upward into the bore (not far, just far enough some of the bristles contact the ring) then push down into the chamber. Go slowly and try to put more bristle into the bore as you feel comfortable...but not enough to stick the brush.

This method has worked then a case shoulder separates and sticks in the chamber. Just use a stiff cleaning rod and go slow!
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rebel
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Re: Case mouth ring separation

Post by rebel »

Late to the party, but have followed with interest. Not sure what type of borescope you have, if you were close I'd take a look with the Hawkeye at my shop. I wonder - could it be a carbon ring buildup with bits of brass in it? Carbon can fuse in the throat and cause issues that you describe. I would use a good bore solvent, jb bore paste and a good carbon remover like Kano Kreen and with a short stiff rod, clean hell out of that chamber. Brush it, patch it, try an oversized brush as suggested after this treatment and then take a look.
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Okiedelta
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Re: Case mouth ring separation

Post by Okiedelta »

Borescope is a flexible fiber optic, not specific to rifle bores. Problem is that it can’t focus that close. It has a side look mirror as well, but that is no help because of the focus.
Doubt I am close to moonshine country, at least not geographically.

Tried the rod/patch/brush. No joy. Even used an M1 Garand combo tool with a very stiff chamber brush, but no change.

The barrel is new with less than 100 rounds through it. Scope pics show very clean barrel.

I’m resigned at this point to wait for the cerrosafe at arrive (should be tomorrow if cousin Larry Potterfield is right) and get a chamber cast, which I hope will pull the brass out with it, or at least get me a better idea of chamber dimensions.
Okiedelta
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Re: Case mouth ring separation

Post by Okiedelta »

So what does it mean if certain cases are shorter after being fired?

All of the rounds I fired and chronyed that day were resized 5.56 cutdown cases. All were LC or FC, except for the last 5 ( including the last round that couldn’t go into battery and froze the BCG) which were PPU 223 cases. All had been prepped the same and had same case dimensions, same bullet (208 g Hornady HPBT Match). (PPU cases had previously been prepped and primed for reloading as 5.56 rounds, so I had to cut them down and full length resized for 300)

So I went back and measured the cases on the last 4 rounds (PPU 223) and each is SHORTER by several thousandths. Fired case lengths are 1.350, 1.353, 1.351, and 1.349. How is that possible? Assuming these were short cases to begin with ( improperly trimmed by yours truly) would that create a situation where the case mouth could be thinned during the shot and leave pieces behind?”

The other rounds from that day are right at pre-fire dimension for case length. Maybe a thousandth longer on a few.

I use the WFT which always gets me consistent trimmed lengths within 1-2 thousandths of each other.
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dellet
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Re: Case mouth ring separation

Post by dellet »

If you go to the top of this handloading page there will be a thread with known problem conversion cases, PPU will likely be one listed as no-go. The reason for this is the brass in the neck is too thick to chamber once a bullet is inserted. That should have shown up when you measured the loaded rounds for certain and possibly empty. The necks would have been a larger diameter.

Anything over .334" loaded or .326" unloaded is a potential problem. Checking thickness they should be less than .013" but .012" is better.

They will also size different because of the greater thickness or unless you measured them before and compared to the LC/FC brass you won't know. There is a good chance that the reason the end of the necks came off was because they were pinched between the bullet and the chamber when fired.

This is all assuming they are too thick.
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golfindia
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Re: Case mouth ring separation

Post by golfindia »

A 762x39 broken shell extractor works with some finagling.
Okiedelta
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Re: Case mouth ring separation

Post by Okiedelta »

Finally got a chamber cast done tonight and made some additional measurements.
The cast didn't bring up any brass, or show any 'ring' or other debris around the case mouth area in the chamber.
Image
Image

After the cast I was able to get what appears to be full seating for both a commercial loaded round (Hornady) and a resized but unloaded PPU Rem223 brass case, and the firing pinless bolt locks with relatively easy hand pressure.
Image
Image

So I have no answers, but all appears to be working and fitting appropriately.

The only remaining anomaly that I found was the presence of brass shavings inside the cases after trimming with the WFT. Even though I tapped each case upside down after trimming to remove any shavings, I found that on some cases that I resized and trimmed (while I was trying to figure the whole thing out) brass shavings would remain inside the case mouth, like this:
Image

Best guess is that there was just enough lube/wax inside that the shavings stuck, and could have been either pinched between the bullet and neck, or came out with the gas as the round was fired, and with shorter necks, the hot shavings could have maybe piled up at the shoulder ridge in the chamber? Seems like a stretch, but that's all I got.
Okiedelta
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Re: Case mouth ring separation

Post by Okiedelta »

Plan is to reassemble everything, head out to the range with some commercial rounds and some reloads, and see if things are running properly. Will be checking fired cases after each round, and running a chamber brush from time to time to see what might come out.
I really appreciate the patience and the outstanding feedback. I am grateful, though unlikely I fear to be of much help to others given the talent and experience here.

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