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A fellow at the range was scratching his head over this dent.  7mm/08, Rem 700, custom barrel, long throat, 140 spitzer, 0.030" off the lands, Varget 2gr below max., fire formed then neck sized, (second firing), this case measures 2.032", no pressure signs on case head or primer, all shots were in 2" groups at 200yds Three cases out of 18 dented, AFTER firing. Lube dent comes to mind first but the dent is too deep and excess lube will leave a few small dents usually. No smoke or blow by. Any thoughts? | ||
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Gas blow back past a neck that fails to obturate properly. Can be due to case work hardening or simply hard brittle cases, too light loads or even hangfires The case collapses because of pressure exerted from the outside of the case. Solutions are to anneal cases but this can also be a sign of being one step away from a blow up! | |||
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PLUS 1 This Happened to me while forming cases from .300 WBY to .375 AI. It appears that the necks work hardened and were not expanding sufficiently to seal the chamber upon firing. The gases took the path of least resistance and flowed back to the case shoulder denting it. I annealed the necks and refired the cases without any further problems. Hip | |||
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If you think your cases are weird. Below surplus Pakistani click.........................................bang .303 British ammo and opening the bolt before the bang.  | |||
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 Have had this happen a number of times. Have always felt it was trapped powder outside of the case.  Roger  Old age is a high price to pay for maturity!!! Some never pay and some pay and never reap the reward. Wisdom comes with age! Sometimes age comes alone.. | |||
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Shooter claims it was only the second firing on the cases. I don't see any soot from blow by. | |||
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I haven't had a dent in the shoulder but sometimes see a smoking of the forward end of cases. Is this a variation on that theme? | |||
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 Personally I doubt it. Almost all my reloads have a varying amount of soot on the necks and some times shoulder. Mild loads are the worst.I attribute this to not religiously removing all the sizing lube, annealing infrequently and some times combining these with down loading. roger Old age is a high price to pay for maturity!!! Some never pay and some pay and never reap the reward. Wisdom comes with age! Sometimes age comes alone.. | |||
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Thanks Roger, I usually wash the cases in Shellite (white gas?) after resizing, so it shouldn't be lube. On the other hand, I've not got into annealing (so far) and rarely get much above starting loads. | |||
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Dan 416 I'm having a similar issue with one of my loads. I don't believe it is gas coming around the case and denting it because there is no smoky residue of gas. I was told that the load was too mild but not sure I buy that either. | |||
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I don't see soot or smokey residue on the outside of this case. So blow by is hard for me to accept but it may be the cause. The fellow claimed this was only the second firing on the cases so work hardening does not seem plausible either. Hard necks plus a light load leading to no obduration thus allowing blow by makes sense, but wouldn't there be soot on the case? | |||
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Similar "look" came from .375 Wby when the bullets got seated deeper than original by recoil (in magazine). _______________________ | |||
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I have read somewhere in a loading book that this is the result of light loads but no explanation on what is actually taking place. To me these dents look to be caused by vacuum, something similar I have seen in vessels subject to a vacuum where the weakest point in a tank etc., collapses inwards with nice rounded edges. Usually a collapse from external pressure has sharper edges. Perhaps with a light load a phenomenon occurs where the powder ignites and starts the bullet on it's way but does not burn quick enough to keep a positive pressure behind the bullet which has been shunted up the bore and acts like a piston, creating a momentary vacuum in the case which is not ironed back out as the powder continues to burn. Also explains lack of soot or external burning too. It is a fact that there is a relationship between burn rate and pressure with gunpowder where pressure needs to build to ensure proper burn of the powder. I have seen these sort of dents before and always has only ever occurred with light loads of certain powders. This is my theory of relativity anyway  | |||
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eagle That is exactly my thoughts on the matter. As I said I am experiencing that in my 400 Whelen burning IMR 4895 pushing 400 grain bullets, however the load isn't "light". | |||
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Maybe a combination of freebore and the loading characteristic. I have used, not owned, some of the Heckler and Koch firearms that had fluted chambers and the ejected empty casings of course had fluting impressions corresponding to the chamber. I do recall that the cases were always blackened a little in the flutings indicating that the cases were not fully sealed in the chamber and leaking gas was fluting/denting the cases from the outside, the very reason why H&K used fluted chambers to allow their rather violent roller lock bolt system to extract cases without ripping rims off. The lack of discoloration on the outside of the cases shown by Dan416 really does point to case collapse causing the dents and not pressure outside the case. | |||
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^^^This. Zeke | |||
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I have read this explanation before but for the love of me I cannot wrap my head around a negative pressure phenomenon in the ballistics cycle ? This would mean that chamber pressure has to be negative and mean barrel pressure positive ? I have never seen a Able-Noble curve with a negative deflection ? No I think that without proper obturation by the neck either because its too stiff or because the peak chamber pressure is too low to properly expand the brass gas bleeds back, causing jetting and concentrating pressure at a point on the the shoulder and collapsing the case. | |||
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WRT the idea that a vacuum caused the dent. Has anyone seen, anywhere, a pressure curve with a negative pressure spike? And if so, where in the trace did it occur? | |||
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I have seen the same dents twice now, first time was a 7STW with reduced loads, some were sooted some weren’t with dents exactly like that, second time was with a 7RUM we tried to duplicate the muzzle velocity of the factory of the tier 1 factory ammo, it was a complete disaster. Dented and sooted cases all the way to the base. I’m pretty damn sure it is a case of under-ignition causing the burn to hesitate, if there is no hangfire occurring then it is there, but not audible as a click-bang. The only other cause is a powder that isn’t burning progressively the way it should, it starts, then stops then starts again causing the case to not expand enough and the gas escapes around the neck. Cheers.  | |||
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I've seen this a couple times. They talk about it ,complete with pictures in a couple of the Speer loading manuals. Speer # 10 manual for sure. A couple contributing factors will cause this. Work hardened case necks that do not expand to seal gas from the case fast enough and allow some gas between the case and the barrel. A low pressure load again not expanding the case neck quickly enough and allowing some gas to leak past the neck.Overly long freebore and very slow powders will also contribute to the same problem. In every case I've seen annealing the case necks and increasing the powder charge a couple grs ended the problem. | |||
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Very interesting. Last week I was shooting my recently acquired 470 Nitro. One case - 2nd or 3rd firing - had a similar dent but ONLY ON THE NECK. I cannot figure why it happened. Only one case. It was full power load - probably around 45,000 psi if not more. "When the wind stops....start rowing. When the wind starts, get the sail up quick." | |||
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Low pressure is my guess | |||
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Can you show us a picture of that ?? | |||
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I have just had another read and look at this post and I think this actually supports my theory of a vacuum occurring in a case that causes the sort of dents shown in the 7mm08 case by Dan416. What I think has happened with the 303 British case is that the primer has fired and started the bullet into the rifling thereby 'sealing' the front of the case, the powder not igniting immediately to continue to build pressure but has ignited just as the bolt was opened bursting the unsupported head of the case. The expanding gas has escaped out of the case and chamber ultimately initiating a vaccum as the gas cloud has cooled and collapsed causing the front end of the case to collapse with dents exactly as we see on the case shown by Dan416. There is no soot on the front of the 303 case as we see at the head that would indicate outside pressure forming the dents, in fact there is no soot on the case walls forward of the ruptured head. Not a betting man but in this case I am feeling safe that we are seeing the phenomenon of vacuum causing this type of denting. Some of the old reloading manuals have information that has been proven incorrect in later years so not everything they say is correct. | |||
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NOpe, that kind of a deep dent 9 time out of a 1000 is too much lube and the dents get larger with milder loads, its gas flow back as a mild load does not cause the brass to fit the chamber. It,s sometimes entertained by a blackened neck, and a case that has set back without proper expansion gas flowback is excessive.. Ray Atkinson Atkinson Hunting Adventures 10 Ward Lane, Filer, Idaho, 83328 208-731-4120 rayatkinsonhunting@gmail.com | |||
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Close your mouth and suck in Jim, your cheeks will look just like the front of that case, hopefully the top of your head won't blow out like the head of the case though  | |||
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I just had one out of 15 or so similar to this in my .358 U/Mag. Load: 250gr Speer with 95gr 4831sc. No way in hell this was a light load. I believe this shot registered 3206fps. This dent is longer, and below the shoulder, top of shoulder itself shows 3 dents from the top. Just the one out of about 40 shots thru the rifle so far. Starting load was 90gr 7828, 15 shot avg 2884fps. All the rest have been heavier loads. Except a couple hundred cast 38 pistol bullets for fireforming. ALL cases were annealed and air cooled as I found 70% quenched still split the necks when necked up from .300RUM cases. Never had a single one split of the 400+ air cooled. IF someone will pm me your ph# I can text a picture of it in hope's it can be posted here. Thanks, George "Gun Control is NOT about Guns' "It's about Control!!" Join the NRA today!" LM: NRA, DAV, George L. Dwight | |||
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Brass is one metal where quenching in water has no effect on the annealing process other than it halts the annealing process instantly. Possibly you are quenching your cases too quickly thereby you are not allowing the heat to complete the annealing process, or possibly your temperature is a little low and annealing takes a bit longer to achieve. Air cooling is fine for annealing provided the rest of the case does not get too hot and soften which doesn't seem to be an issue for your cases. As to the dent issue in cases, I still maintain it is something to do with the ignition process where there is a momentary collapse in pressure. | |||
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I've argued this endlessly. No annealing at all of used brass from unknown firings. About 20% split necks. Quenched cases SPLIT 70%. Same annealing air cooled: 450 NOT A SINGLE ONE SPLIT. I also have a metallurgy education in college with LOT's of comparisons of various metals. I've reloaded since 1958, couple hundred thousand rounds. George "Gun Control is NOT about Guns' "It's about Control!!" Join the NRA today!" LM: NRA, DAV, George L. Dwight | |||
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With due respect there is endless articles on hardening and annealing of metals if searched on the internet and from all I have read without exception make the point that brass is one metal where quenching after heating to anneal has no effect on the softening process. Here's one such bite of that information; "In order to make steel harder, it is heated to some temperature, and then cooled fairly rapidly, although this is not always the case. Brass, on the other hand, cannot be made harder by heating it--ever. Brass is always made softer by heating. The only way brass can be made harder is to "work" it. That is, the brass must be bent, hammered, shaped or otherwise formed. Once it has been made hard, it can be returned to its "soft" state by annealing. The hardness of brass can be controlled by annealing for a specified time and temperature. Unlike steel, which will be made harder when it is cooled rapidly, brass is virtually unaffected when it is rapidly cooled. Annealing brass and suddenly quenching it in water will have no measurable effect on the brass. Cartridge cases are made of brass. When cartridge cases have been reloaded a number of times, the case necks become harder. Annealing will return the cartridge case necks to their factory original state." The standard annealing practice for most shooters is to heat and quench their cases to prevent the possibility of softening the case past the shoulder area. I do so for my 404 cases and have done so for years and if I don't get lazy and reload cases too often between annealing I have no problem with case neck or shoulder splitting and some of my cases have been loaded countless times from when I acquired them in the early 80's. I can't explain why you are finding different with your annealing process. | |||
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Eagle: Forget all you've ever read about this and do the test yourself and see as I DID. George "Gun Control is NOT about Guns' "It's about Control!!" Join the NRA today!" LM: NRA, DAV, George L. Dwight | |||
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George: Interestingly the instructions for the Annealing Made Perfect annealer say to air cool; granted, they have a very specific induction heating program for each type of case, brand, and even neck thickness, but I thought your comment interesting in light of this. Have never had a split neck since I started using AMP and my neck seating tension is much more consistent. I have two rifles that have SDs less than 5. | |||
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George I don't know how I can do the test as you suggest as I quench in cold water and get no splits so if I annealed and air cooled and got no splits I'm no different. I am really amazed with your statistics. "No annealing of used brass about 20% split", this seems high. In all my years of reloading various cartridges with used brass I have had no problems with split cases certainly not to the degree you seem to be having. Maybe 300RUM cases have a propensity to split for some reason? I anneal my 404 cases especially the Kynoch cases as I get about 1 in 5 split on firing old factory rounds (this is 1960's Berdan primed ammo made before the Kynoch factory ceased production). Once I anneal the unsplit cases along with my many times fired RWS cases (these were produced in the 70's) using water quenching I have no problems with split cases. Those cases that have split, Kynoch factory and RWS where I shoot too often before annealing, I silver solder the cracks in the necks, anneal, cold water quench and carry on happily using them. Your statistic of 70% cracking after annealing and cold quenching is indicating your annealing is not correct or there is something radically wrong with the brass. Most everyone who starts annealing does so with standing cases in water, heat until the neck changes colour, then tip over in the water, a cheap and simple process recommended in reloading manuals and by many learned reloaders. There would be a lot of highly pissed off reloaders out there if they got 70% split cases after annealing this way!!!!!! Something just doesn't stack up with the issue you are having with quenching. There are better people around than me who have metallurgy experience and it seems without exception they all state that brass is not hardened with quenching. As I said at the start I cannot duplicate your example as I don't have any issue quenching after annealing my cases. I would air cool if it was going to provide any benefit but at the moment I tip my annealed cases from the heat sink holder in my drill and it is just easy to tip into a container of water where nothing gets burned. | |||
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Actually Eagle, the guys at AMP have done more research on annealing than anyone I know of, and they specifically state cooling in water is not necessary. BTW, the whole purpose of annealing is not to harden the brass. | |||
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Actually the whole purpose of annealing is to soften brass. I don't think that anyone said that different annealing techniques will harden the brass. I've been reloading for rifle match shooting in different disciplines for about 30 years and I don't think that I've split 20 cases in that time. Don't work harden your brass. I limit the sizing and expanding of the necks by using bushing dies, remove the neck expanding plug on the decapping pin and minimally size the cases. Frank "I don't know what there is about buffalo that frightens me so.....He looks like he hates you personally. He looks like you owe him money." - Robert Ruark, Horn of the Hunter, 1953 NRA Life, SAF Life, CRPA Life, DRSS lite | |||
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Yes, I misread Eagle's post; thanks. | |||
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That dent was not caused by a vacuum. On this planet, the highest pressure differential you can get by "sucking" is around 14 psi. That's not enough force to dent a piece of brass like that, unless the brass is nearly molten. The dent in the picture (which is still on photoSuckit?!?) was caused by gas pressure pushing between the chamber and the outside of the case. This gas came from inside the case and leaked around the neck. There are a few contributing factors for a neck that doesn't seal as others have mentioned. One thing I have not seen mentioned is a deep scratch or possibly an erosion cut in the neck of the chamber. If you look at the fired case you can make out a line, and if we could scope the chamber I bet you'd see some sort of groove that is making it difficult for the brass to seal:  Also, to the guys talking about annealing cases. The only way to make cases harder by quenching in water is if the cases are made out of steel. | |||
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