Sierra's recipe suggested a Rem 9 1/2 M primer. I used a CCI Magnum Rifle. Can't imagine this being the culprit and nor could the folks as Sierra.
I might buy the argument that there was something foreign in the chamber if I was out in the boonies with wind and debris blowing around to beat hell AND if I noticed any (abnormal) resistance when closing the bolt on the second round. Since I was in a clean, rifle range environment shooting from a bench and felt no resistance, I think we need to dismiss that as a possibility.
Same goes for lube in the chamber since this was the second round. If excessive lube was the issue, which it couldn't be since the rifle had been cleaned, to include barrel, chamber and lug recess, I think it would/should have more likely occured on the first round.
I went back through my loading notes last night. My dented case (wish I had taken a picture - looked just like yours) was the 16th one fired that morning. I was doing load workup on my 6.5-06AI using 120gr Nosler BTs and RL22.
Everything was progressing normally, and I was just approaching what I thought would be a max load. The first load from that charge weight gave an error reading on the chrony. Not unheard of with the cheaper Shooting Chrony, but fairly rare for mine to give an error. Case looked fine, bolt lift was fine, primer just starting to flatten. I figured a cloud had blocked the sun or something, causing the chrony to misread, and sent the next one downrange. This one sounded "different" and got no chrony reading again. When I ejected the case, bolt lift was fine, but the case was dented just like yours...I stopped firing right then.
I eliminated case lube denting, as these had only been neck sized with dry lube, then tumbled clean. The round was perfect when it went in, but dented to heck when it came out...
The chamber was fine; I looked right then, just to be sure, but had no problems with previous 15 shots. Back home, I decapped that piece of brass and found a particle of tumbling media partially blocking the flash-hole. Must have been it. I've been anal about double checking that ever since, and have never had another problem with it. I chalked it up to hangfire/delayed ignition of powder charge....
Allen, I have had that happen about 2 or 3 times now, out of a couple of hundred hand loaded rounds, in my Sendero (older version) 300 RUM. One was not quite as large as your dent (almost) and the other(s) a little smaller. I have no idea why it happened other than there may have been something in the chamber or on the case. They were warm loads of Retumbo and not sure if it was 180 E-Tips and/or 210 Bergers.
My brass is also well prepped, turned and trimmed necks. Fed GM215M primers.
I will tell you this... I loaded the cases back up and I very clearly remember the larger dented one resulting in about a 6" flier at 427 yds. The dent came right out. If you want to reuse the brass, put it in your fowler pile until it is fireformed out again.
Thanks fellas. Great input. I just knew that this must have happened to other shooters on this forum. Unfortunately, it's seemingly still a mystery as to the cause.
I'm going to try launching the 190 SMK's with both RL-25, Retumbo and maybe H-1000. I think I've got 500-600 of 'em on the shelf anyway...might as well get busy and figure out what this (as yet) safe queen really likes to bang steel with out past 1k.
Well I just went through this today. 700P in 300 RUM, 155 bergers on 90 grs of H4831 sc. With the problems finding primers over the last year I ended picking up a couple K of Rem 9.5 M, my original load was with WLRM primers. I had 8 rounds of the Winchester primed rounds left. I fired 2 w's to foul, after a brief cool down fired a rem. round, got that big case dent. WTH? Fire a W round looks fine, fire a R round big dent, alternate ad nauseum. Other than the dents and being 2" R-2" D, the R 9.5m shoots an identical little bug hole. The primers are the only variable that's changed. Looks like I need to hunt down some WLRM primers, even if it means eating a hazmat shipping charge.
unless you are getting some kind of hang fire due to improper primers
I agree, I was often getting the exact same case dimple near the neck as in your pictures with the first 1-2 shots in a clean barrel using CCI BR2 primers and 4831SC in a 6.5x55.
In hammer and bench testing the primers I found 1 in 3 was much weaker than "normal", I just think I had a bad batch, I chucked that brick of primers :cry: and got some RLRM, no problems with case dimpling anymore.
IMHO the case neck dimple is caused by too weak primer to ignite a slow powder completely, then the powder grains ignite a few inches down the barrel and suck the case in?
Anyway 300RUM almost certainly needs Fed215 primers.
I have had one event like this while loading for a 7mm ultra. A buddy purchased a used Rem 700 and after a thorough cleaning and inspection I discovered his rifle had what I thoucht was an abnormally long throat. Be it from a huge amount of free bore from factory or the previous owner melting quite a bit of the lands out of it, a 160 gr. accubond would not touch the lands until well out of the case mouth. I thought it was odd as my Sako does not have near this much freebore. We just seated them to mag length and loaded several diferent charge weights of Retumbo. The first round with book start load went across the chrono rather underwhelmingly i thought but no strange sounds or other conditions were observed. Upon opening the bolt I went numb as I saw the case that flopped out! Just below the shoulder were dents almost identical to yours but five of them all around the case, however, there was alot of black on this one. After much thought and discussion I determined that it had to be due to the low "start" load and extreme jump to the lands. What I believe happened is that upon firing while the bullet was "floating" in thin air before engaging the rifling, the low charge of powder did not develop enough pressure to expand the case to chamber dimensions to form an effective seal and some pressure caused the case to deform inwards/ implode somewhat. Upon reaching this conclusion we moved up to the next charge weight with me driving, as it was my conclusion, and never had a hiccup again all the way up to book max. Low charge weights in those big cases are no good, combine that with his long throat and I believe book start was too low for his particular situation as I have never seen it before or since. Could be a hair brained conclusion but makes sense to me.