Any ideas what is happening to my 7mm rem mag brass. Not running huge pressure/load but the base of the case is splitting a few mm up from the belt to varying degrees. On their 3rd load and annealled between 2nd and 3rd
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Any ideas what is happening to my 7mm rem mag brass. Not running huge pressure/load but the base of the case is splitting a few mm up from the belt to varying degrees. On their 3rd load and annealled between 2nd and 3rd
Attachment 201354
Case head separation can be cause by over sizing them
I am only bumping shoulder by 2or3 thou, should I just be neck sizingQuote:
Originally Posted by Kelton
only bump it as much as you need to be able to chamber freely..... and PLEASE paperclip test ALL your brass before loading it up from here on in.....
its a real pain in arse if you get a seperation on day one of a hunt....or at any other time....
Interesting I believe this is also a contributing factor in people not liking belted cases I never had the issue with 7RM I lost my brass pretty quick though. Nope neck sizings the pitts . Their is a particular die for belted cases but I’m not clued up on what the go is their sorry I wouldn’t a clue how much shoulder bump I’m giving I set my die so the bolt just closes freely and call it a day . That also may be considered a lot of shoulder bump if you have gone that far from new?
Paper clip test being feeling for a bump inside the case where the split is then checking other cases for the same bump?
Should be able to run the paper clip up and down the inside of the case with no snagging is my take on it
sharp pointy paper clip with a right angled bend in end about 3mm long...scratch the inside of case as hard as you can....if there is a fault it will "catch" try it on the ones that are buggered and you will soon feel what the go is.
Have you had to trim them?
Get a cheap set of oring picks. Think I got mine from workshopinnovation.co.nz.
After my first separation I started checking all my brass for that particular rifle.
Sav 99 in 243 with a tight chamber could see a ring forming on the outside.
Dumped all that old brass as well and started with fresh stuff.
2-3 reloads does not seem like a lot. Lots of possible causes, try a different brand of brass next time. And only size just enough to allow the bolt to close.
I will sometimes take one case and starting with just neck sizing it and checking to see if it will chamber, if not then start gradually bumping the neck until it Chambers.
Nb my other sav 99 and the bolt actions I load for have never had a problem.
Z
Any pictures of the case head?
What's your cleaning regimen like as a dirty chamber can cause overpressure issues as well.
Looks like there's a hole in that case to the right?
Yes I trimmed them at 2nd firingQuote:
Originally Posted by JohnDuxbury
Will post up a pic tonight of case head - I clean the rifle every 25 or so rounds.Quote:
Originally Posted by Rated M for Magnum
No pressure signs on primers. The case has a small hole after last firing on the right side case
It sounds like your sizing is ok but you could bump the shoulder less to try and improve the life of the brass.
What brand is the brass?
It could be that the rifle has generous chamber and or headspace dimensions and most of that streatch is happening on the first firing.
What does a new vs fired case measure to the shoulder?
Is it Federal brass ?
There was a batch approx 3-4 years ago that was really bad for this
I don’t recommend federal brass in rem mags anymore as a result
Nah its hornady. I am tempted to bin the lot - will see how it comes up on next cleaning/sizing/trim.Quote:
Originally Posted by 7mmsaum
Greetings @nigelp,Quote:
Originally Posted by nigelp
How are you measuring your shoulder bump? It takes a lot more than 0.002 to 0.003" of shoulder head space to crack a case like that in three shots. Belted cases can be an absolute pig for head separations due to the belt recess in the chamber being too large for the actual belt. The case can still chamber hard with the shoulder sized to fit in the chamber. The only fix for this is to size the case body just in front of the belt separately from the rest of the case. There is a special tool for this but a friend got by with his .308Norma Mag by using a .300 Win Mag die that only sized the base. Some case makes can be bad for this. Others should be able to comment further on this. There is a reason that all the latest hot shot cartridges don't have a belt.
Regards Grandpamac.
Reason I ask is my brother had a similar problem in his rem mag, he wasn't cleaning the chamber or neck area. The necks of these cases all look filthy.om these pictures and this could be your problem.
Yeah I didnt notice the split case when I fired it (dropped on ground after) and would have left residue in the breach from the case crack. Will give it a good clean and see if it sorts itself! But also try the paperclip test tooQuote:
Originally Posted by Rated M for Magnum
Experienced a similar problem with about a dozen Hornady cases, out of a box of 50. All of my other Remington and Norma cases, all treated the exact same way, are fineQuote:
Originally Posted by nigelp
I treated reloading my 7mmRM the same way I load unbelted cases. Normally neck size but when needed bump the shoulder back just enough to chamber with a slight pressure when closing the bolt. Not tight but enough to feel resistance.
Hornady brass in rem mag is bad for splitting the necks too, starts at the case mouth
Greetings again all,
I could have been clearer in my earlier post. The early head separations in belted cases can be as much a rifle problem as a case problem. The belt recess in some belted chambers is cut overlength and the belt on the case can be undersize. The case just ahead of the belt can expand into this space. If the case is then sized just enough to chamber we can set the shoulder back to create excess headspace to the shoulder. If we set the shoulder back the optimal 0.002" using a comparator and not by feel then the case won't chamber due to the bulge in front of the belt. The bulge needs to be dealt with seperately.
When the US major manufacturers started developing their own line of magnum cases after WW2 they all had belts because the American public believed tha a magnum case had to have a belt to reinforce the case head. This was all crap of course but loose tolerances for the belt and the shoulder of these cartridges plus skimping on brass has resulted in the problems with head separations that many handloaders have today.
Regards Grandpamac.
I always thought belted cases headspaced on the belt, the shoulder was irrelevant. I can see having it headspace on the shoulder would possibly lead to issues,
The belt is only good for a fatique riser - a point in the brass where there is a sharp transition in wall thickness. It's a hangover from the old African big game rifles where the cases did headspace on the belt as there wasn't a shoulder on the case at all. As people started using these big cases and necking them down to create the 'magnum' rounds we have today the belt remained. Only a few like the Lapua magnums got rid of the belt.
As grandpamac has noted, if the belt on the case is short and the belt recess cut in the rifle's chamber is long, there's a chunk of case wall that isn't supported. You can't fix that. It will result in a split eventually whatever you do...
The usual thing done these days when reloading the belted cases is leaving the shoulder alone until it contacts the shoulder cut in the chamber and it becomes stiff to close the bolt. Push the shoulder back just far enough to reduce the pressure on the bolt when chambering. In effect, you are making the belt irrelevant and decorative, as you are then treating the case like a normal no-belt case and headspacing on the shoulder. Neck sizing to take the next bullet can be done as a separate option - there are bushing dies like the Redding as one example, that you can get as a 'full length' bushing die. You can set the die just to the point of pushing the shoulder back so there's no pressure when chambering a reloaded round. The bushing can be changed to the right one for the neck tension you want and you don't need to run an expander ball that is hard on the case neck.
That helps brass life for the case neck splits, but won't do anything to solve the separation problem. Unfortunately that's a result of the design and the cut out in the chamber...
As per Grandpamacs post above sloppy headpacing and generous chamber dimensions could be part of the problem hence my asking for new vs fired shoulder lenghts.
With the abundance of old military 303s (which headspace on the rim rather than the shoulder similar to a belted magnum) around and interchangeable bolt heads a lot have excessive headspace and will case head seperate in as little as one or 2 reloads unless some care is taken.
If on the first firing a appropiately sized oring is stretched down over to the rim so that when chambered the round is firm to tight to close the bolt on and the case is held firmly against the bolt head then on first firing it will stretch out to chamber dimensions without streatching lenghways in the critical web area and from then on it can be neck sized or minimally full lenght sized so that it remains now headspaced on the shoulder.
In this way the brass can be reloaded many times till usually the necks split.
However the brass will only fit that rifle or one with worse headspace.
If sloppy headspace is an issue this could be your fix or another way to go about it is to neck up the brass from new then size the neck back down only sizing the first part of the neck creating a "false shoulder" to headspace on.....it needs to be at the point of a tight bolt close to resist primer strike driving it forward.
As for the brass you have definitely check with probe....unfortunately once it streatches in the web junction there is nothing you can do to put it back.
The SAAMI dimensions for the 7mm Rem Mag show a headspace dimension to a datum on the shoulder but the tolerance between min case and max chamber is larger than beltless cases. My calcs give it at 0.661mm v the Creedmore at 0.362mm. This together with the tolerances for the belt means there can be a gap between the front of the belt on the case and its recess in the chamber. This together with the lighter cases of some brands is the root cause of the problem which often catches new handloaders out. I think that I have only loaded for one belted case (.350 Rem Mag) and that one briefly. There probably won't be any more.Quote:
Originally Posted by Marty Henry
Regards Grandpamac.
I don't reckon it's true you can't get life beyond a couple firings. If you induction anneal and use a rear collet die to bring the bulge back in you should get it to the point of a loose primer pocket (at least 5 or 6 firings or more).
BTW, annealing has nothing to do with the brass 'hardening' after being shot, it's actually your re-sizing of the case during the reloading process which you are attempting to stress relieve from.Quote:
Originally Posted by T.FOYE
Lol Im no expert on metallurgy eh. You're probably right right but for whatever reason annealing does vastly improve case life especially for the 7mmRM. Having said that I do make sure to paperclip the inside of each case.
Spot on,Quote:
Originally Posted by T.FOYE
You need to deal with any bulge just in front of the rim seperately and prior to sizing the rest of the case. You can do this with a bulge buster kit or a stripped .300 Win mag die, the former being best. You only need to do this if you have a problem as some rifle case combinations will be fine. Once the bulge is dealt with you can full length size to get your required shoulder bump. The crack develops not through work hardening but from case stretching. Each time the round is fired the cartridge is shunted to the front of the chamber by the firing pin with the primer finishing the job. As pressure builds the case head is forced back to the bolt face with most of the case body stuck to the chamber walls. All of the stretching happens in a small area a short distance in front of the case head resulting in a thinning of the brass at that point. This happens inside the case and will show up as a bright line on the outside. One more shot and the case separates (cracks) at that point. Sometimes the case extracts OK but sometimes the head pulls of the case leaving the body in the chamber. Something to be avoided at all costs. Far more than one chamber has been ruined trying to dig the front of the case out.
Regard Grandpamac.
