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Thread: Question on why my 243 case necks are cracking

  1. #1
    Boolit Master Tripplebeards's Avatar
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    Question on why my 243 case necks are cracking

    To give the history on the brass it was given to me. I don’t know how many times it was fired previously and how old it he brass is. I annealed all the brass about 2-3 firings ago. I am bumping the shoulders back approx 3000 th’s. They are all RP cases. I trim the necks every time back to minimum length as most have grown during firing. I have fired them in two different BCA 243 uppers. They have been sized each time in my small base RCBS sizer die. Is the brass getting worked that much after 2 to 3 firings that they are cracking already? It seemed after every firing I’ve been loosing around 3 to …or more, out of maybe 50 to 60 casings, to neck cracking. I would assume I need to Anneal them again…maybe after every firing? I have shot 243 RP casings umpteen times my bolt actions and can’t recall have a cracked neck in any of them.





    I have the rest prepped ready to load. I’m wondering if I should anneal them before I prime and load? I always anneal before sizing the brass so it’s kinda backwards. Just wondering if it will save a few cases by doing so?

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    Boolit Master Moleman-'s Avatar
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    Look at the two lugs in the barrel extension on either side of the extractor. Upon the start of ejection the case is being pushed towards those two lugs. Upon clearing the chamber, the The inside front corners of those two lugs are the first thing the case hits. You often see a dent/divot near the shoulder area and heavy scratches on the case necks. The scratches are a weak spot for them to crack the next firing. I try to remember to take a diamond hone and just remove the very sharp corner that causing the issue, it doesn't take much and just to look at the lugs they'll look basically the same. You're probably getting brass glitter in the extension from those two sharp surfaces.

  3. #3
    Boolit Master Tripplebeards's Avatar
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    The case necks do have long scratches on them. Any links or YouTube videos on how to do it?

  4. #4
    Boolit Master Moleman-'s Avatar
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    I didn't see any youtube videos. So, grabbed a new extension and just dehorned it. Couldn't find a bright finished ar10 extension (know I've got at least one out there) and the darker finished one in the bin didn't show up well in pics. This is an ar15 extension, but same thing. It's best to do this with the barrel off of the upper, but it can be done through the ejection port, but you risk damaging the finish on the upper. I try to remember to dehorn them before installing them on a barrel as it's even easier, but sometimes I forget until they get test fired and it's apparent that the two lugs on either side of the extractor are sharp. You don't have to remove much metal and if you have a Dremel, a 5/16" or 3/8" cratex bit will knock the corners off without too much risk of taking too much off.

    Pic one the arrow is pointing to the slot that the extractor rides in. The lower lug in that pic showed up better where the tip of the 3 sided corner has been rounded off. Pic two just shows the top corners of the "extractor slot" in the extension have also been similarly rounded. You just have to dull the sharp edge, you don't want to reshape the lug. Also good to hit it with a felt bob with a little red rouge on it to smooth it up afterwards. The allen key is in the index pin hole for reference.
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  5. #5
    Boolit Master 243winxb's Avatar
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    Could be a bad brass problem.
    Or over working the necks? Measure the neck OD after sizing without the expander. Measure OD of fired. Measure OD of loaded rounds.

    Sized vs loaded round should have about .003" difference. To get minimual sizing, you need a Redding Type S FL sizing BUSHING Die.

    Neck tension/bullet hold- After seating a bullet, the OD has to get larger by .003" minimum for an auto loader.

  6. #6
    Boolit Master Moleman-'s Avatar
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    It could very well be normal brass issues. The reason I brought up the barrel extension is the scratches and gouges along from before the shoulder to case mouth seem to be in line with the cracks. L-R look at cases 1, 3, 6 and even #7 you can see a slight extension lug shoulder ding in line with the crack. Too much glare on the other cases to see well. There are usually two scratch lines but can also be only one and the heavier ones usually bounce a little to make a series of small gouges. Usually right in the middle of the neck there will be a bigger gouge which is where the cracks start if they're caused by a sharp barrel extension. The case is free from the chamber at that point and the brass is the thinnest there also. The middle case shows what looks like the same sort of gouge caused by a sharp extension just to the left of the crack. Some guys will shorten the ejector spring so it doesn't have as much energy to push the cases into the extension, but I think it's better to just remove the sharp edges that are causing it.

  7. #7
    Boolit Bub QuackAttack24's Avatar
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    Moleman has a good observation about the scratches on the neck brass. It could be a combination of scraping the barrel lugs and overworking/under-annealing of the brass. Something is making your brass brittle. Who knows if the previous owner annealed them, or how many times he re-loaded them before you got them? I anneal my bottleneck brass cases before every re-sizing. It also might be worthwhile checking your annealing process with some Tempilaq to make sure you're getting them hot enough. IIRC you need 800 degrees to get the annealing time down into the few seconds range. Annealing at too low a temperature equals no annealing.

    Another thing you might try is just load up some new brass, make sure you're annealing properly and see if this problem repeats itself with new properly prepped brass. It the mean time, taking of the sharp edges from the lugs seems like a worthwhile pursuit.
    What could possibly go wrong?

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    Boolit Grand Master Char-Gar's Avatar
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    Brass cartridge cases are not everlasting. In spite of all the rehab and first aid we do on them, they will roll snake eyes in due time.
    Disclaimer: The above is not holy writ. It is just my opinion based on my experience and knowledge. Your mileage may vary.

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    Boolit Master Tripplebeards's Avatar
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    I used a fine jewelers file and took a few minutes to lightly go over all the barrel lugs t o remove any burrs and sharp edges.
    I then polished them with my dremel and some mothers chrome polish. I only dinged up one edge of the inside of my upper. I touched it up but its wasnt enough to even worry about. Hopefully it helped a little. I'll make sure to anneal after every firing from now on. I just got done loading up a ladder test and felt a bullet start hard then easy. The case neck cracked when I loaded it. Must have been weak to begin with.

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    Boolit Master Moleman-'s Avatar
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    My son recently bought a 7.5" bca 5.56 upper for his sbr that's leaving decent divots in the necks of new LC green tip along with neck scratches from a rough chamber. If left like that we'll only get 2-3 firings on a lot of those cases before they split. He wants to change the handguard so we'll address the sharp lugs and chamber then.

    Let us know how it does. The cases with the damage are still going to be prone to premature cracking but going forward you should be able to get more loadings out of any new ones.

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  11. #11
    Boolit Master


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    Quote Originally Posted by Tripplebeards View Post
    The case necks do have long scratches on them. Any links or YouTube videos on how to do it?
    I have had long scratches like that on rifle cases. It was caused by grit or something else on the sizing die. I used Flitz paste on a paper towel attached to a cleaning rod that I turned with a drill. I little bit of polishing cleaned the die right up and no more scratches.

  12. #12
    Boolit Master Tripplebeards's Avatar
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    I tried it today. Little to no scratches on my cases!

    It shot pretty good to. It’s a BCA 243 20” 1/8 twist. I loaded up some of the 60 Seirra HPs that I received from a member here. All groups a shot under MOA accept for one. I have about a dozen or so Sierras left. I hope Sierra starts making them again.

    100 yard groups…





    Forgot to take photos of the brass
    Last edited by Tripplebeards; 06-12-2021 at 05:07 AM.

  13. #13
    Boolit Bub QuackAttack24's Avatar
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    Nice, Mad props to Moleman. Thanks for the update.
    What could possibly go wrong?

  14. #14
    Boolit Master Tripplebeards's Avatar
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    Quote Originally Posted by quackattack24 View Post
    nice, mad props to moleman. Thanks for the update.
    ditto!

    I had some light scratches after polishing for the first few groups of three. Then after shooting a few more groups I didn’t get any scratching. I did have on my Caldwell brass catcher and towards the end the brass kept hitting it and not exiting. It did turn it backwards in the chamber so I knew it was completely cycling bur bounching back into my chamber…maybe that helped with not scratching? Anyways thanks to Moleman I’m on the right track. Just need to beg or borrow some more 60 grain Seirra varmint HPs!lol
    Last edited by Tripplebeards; 06-12-2021 at 08:22 AM.

  15. #15
    Boolit Master Moleman-'s Avatar
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    Glad it worked for you. Not all of the ar15/10 extensions will damage the cases like this, but a fair number will. First noticed it with my first ar15 over 30 years ago. When I got a 308 AR years later I already knew how to fix the issue when I saw the neck divots the first time we took it out. The mini 14 and M1A I had since before the AR's would ding and throw the cases pretty good but I wasn't getting but a fraction of the split necks like I was with the ar15/10. Especially the splits in the middle of the neck that don't extend to the case mouth or splits that are on a heavy scratch or divot line. Those middle of the neck splits with intact case mouth are what got me looking real hard at the fired cases and noticing that there were a fair number of cases that were splitting in the exact spot as the divot left from the sharp corners of the barrel extension lugs. Even the case necks that split to the case mouth often had the same divot or scratch line leading to the split.

    The cases with the divots/heavy scratches in them already will be more prone to split, but at least from here forward you'll start getting longer case life with undamaged cases.

  16. #16
    Boolit Master


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    You might also examine your sizing die. I had a Hornady 50BMG die that was way over working my brass causing neck split. The *** die sized the necks down .027 under size then expanded them. After replacing that set of dies and matching Hornady press with one of the early LEE 50BMG Press and die sets the problems went away.

    Check your sizing die without the expander installed and see how much the die is sizing the neck down before it expands it back up.

    Ken
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  17. #17
    Boolit Master Tripplebeards's Avatar
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    I’ll have to measure my necks. I have been using the small base rcbs 243 die set. I also have the green box rcbs 243 die set. I grabbed some different 243 RP cases to start over and watch for signs. I did find that I have been using trimmed cases to 2.020”. I trimmed them to short by accident. I believe my RCBS trimmer adjustment knob came loose like always when applying a little to much pressure with my cordless drill attachment. I made sure to trim the new batch to 2.035”. All the cases, new batch and old batch, I’ve been using are used cases that I don’t know the history of. I annealed the new batch I’ll be using last year. I went to size them in the small base die set and had one neck already split when sizing. The rest all sized just fine. All trimmed to 2.035”. When I chamfered the outsides I still have a little edge I can catch my fingernail on for some reason. I crimp them with a lee collet factory crimp die so the pronounced edges will get pressed down anyways. Wish I could find a bag of new RP 243 brass. I’m guessing it would shrink groups vs my sorted head stamp matching RP cases.
    Last edited by Tripplebeards; 06-15-2021 at 08:34 AM.

  18. #18
    Boolit Master 243winxb's Avatar
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    The edge after trimming can come from a dull cutter head. Or the cutter feed rate is to high. Dont push so hard on the cutter. A little burr is normal before chamfering.

  19. #19
    Boolit Master Tripplebeards's Avatar
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    Thanks, when I seated bullets in the cases today the outer case “lips” got shaved off during the process. I’ll try and trim slower from now on. That cutter was replaced not to long ago from rcbs because of the same issue I’m having again now. I wonder if it’s because i annealed the cases and they are so soft that brass folds back instead of getting cut off?

  20. #20
    Boolit Master 243winxb's Avatar
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    I use some Break Free CLP on my steel Lyman cutter head. I put lube on an old tooth brush. This gets rid of the brass chips & lubes, at tne same time. Every 2nd case.
    Lyman makes a carbide cutter head that would last longer then steel. But i didnt like the carbide cutters price.

    Could be the soft brass? Dont know?

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