Headspace issue or bad brass?

powdergun

powdergun

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Here is the situation

Rifle: Custom rifle not factory. 300wm

First time out with some brass on it's second load. No problems
Second time out no problems
Third time no problems
Fourth time( this would be the fifth reload on the brass). A few case head separations with other brass showning rings.

No sign of high pressure, good primer strikes.
I was load testing for group size at 300 yards and for some reason the impact was 4" lower than last time I tested the loads but groups were fine. Not my best day shooting but the rifle was consistent printing 1 to .6 moa

The total round count is 45 rounds on the rifle and it is only the last 12 shots with the 5 times loaded brass that the issue arose. My suspicion is the brass because if it was the headspace I should of seems signs from the very beginning.

Looking for any and all advice and thanks in advance for the input.
 
Are you full length sizing? That could be the problem.

Treat the cases as if they were rimless, headspaced on the shoulder, not on the belt. That might solve your problem.
 
Consider that whatever re-sizing you are doing is pushing that shoulder back excessively for that chamber? Headspace on 300 Win Mag is typically on that belted shoulder - I think you are describing an issue further forward than a headspace check would explain?
 
Yes full length sizing. I have a neck sizing die for it. Is that a better idea?

The separation occurred about .14" above the belt.

I would hate to think I need to send it back to the smith
 
It is important if you are reloading belted magnum cartridges that you set your FL die so it sizes the case but does not push the shoulder back... if you just screw the die down to touch the shell holder you most likely are pushing the fire formed shoulder back, in effect creating what most people incorrectly refer to as headspace when it is excessive cartridge case head clearance.

I believe that is your problem... and it is a common problem with reloading.

If you are loading fairly hot that will also contribute to early brass failure.

Originally the belt on the magnum case was designed to eliminate headspace problems but the factories have never been able to produce those dimensions accurately. From the forward edge of the belt to the rear of the brass was supposed to measure exactly .220". I have seen new brass measure as small as .214"... which leaves the cartridge with 6 thou excessive clearance to start with...

If you want to make strong cases that will last longer, use virgin brass and enlarge the neck diameter, then size the case leaving a false shoulder where the neck meets the shoulder... enough of a false shoulder that it causes the bolt to be hard to close... that way the case is held hard against the bolt face and when fired the shoulder blows out properly with no stretching of the case. Then when reloading don't over size... you should be able to feel bolt pressure when closing on a sized case...

Long seating a bullet so you can feel the bolt close on a case will not give the same results as the firing pin will drive the case over the bullet and let the case move forward with resulting stretching and a weaker case.
 
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Not loading hot but I think you may have indentified the issue. I have been resizing to the shell holder so probably pushing the shoulder back. I am going to pitch that brass and start with new. What would the best way to size new brass. Neck or full length ?
 
5 reloads is about all I ever get out of 300 mag if I am lucky - I full length resize because I have a number of 300's - I end up trimming twice and toss the brass - usually end up with split necks by reload 3 or 4 - I know I should anneal the necks but....
Btw I can easily reload 308, 243 etc at least 10 times so I figure that is the price you pay for shooting a 300
 
powdergun said:
Not loading hot but I think you may have indentified the issue. I have been resizing to the shell holder so probably pushing the shoulder back. I am going to pitch that brass and start with new. What would the best way to size new brass. Neck or full length ?
Click to expand...

If you want to make strong cases that will last longer, use virgin brass and enlarge the neck diameter, then size the case leaving a false shoulder where the neck meets the shoulder... enough of a false shoulder that it causes the bolt to be hard to close... that way the case is held hard against the bolt face and when fired the shoulder blows out properly with no stretching of the case. Then when reloading don't over size... you should be able to feel bolt pressure when closing on a sized case...
 
guntech said:
If you want to make strong cases that will last longer, use virgin brass and enlarge the neck diameter, then size the case leaving a false shoulder where the neck meets the shoulder... enough of a false shoulder that it causes the bolt to be hard to close... that way the case is held hard against the bolt face and when fired the shoulder blows out properly with no stretching of the case. Then when reloading don't over size... you should be able to feel bolt pressure when closing on a sized case...
Click to expand...

^^^ this is good advice. Belted cases, in my experience, can have up to 0.008" slop, so everytime it is fired after a full length 'to the shell holder' will stretch the case that amount, so 5 firings 0.040" stretch, you will get seperation.

I have a 300 wm that have over 10 cycles on the brass, no incipient separation and primer pockets still tight.

Rifle chambers are not always exact in production rifles.

To that end, I have used the neck up/neck down method to get max life out of the brass. I had a machinist machine a mandrel out of 7/8ths ready rod to neck up 6BR brass so it could be necked down to fireform 6 Dasher brass.

Also, I am thinking of getting a similar mandrel made up that has 0.243, 0.264, 0.284 and 0.308 " steps that are 0.020" over these numbers to expand the necks. It is a one time function for new brass and will increase the longevity.
 
Just tried some new brass. Can't really feel any difference in bolt pressure. Will sizing lengthen in a bit so that it does put pressure ?

I expanded the neck then gradually lowered the die and sized a bit at a time and found no changes in bolt pressure.

Am I doing something wrong or is my chamber too long ?
 
powdergun said:
Just tried some new brass. Can't really feel any difference in bolt pressure. Will sizing lengthen in a bit so that it does put pressure ?

I expanded the neck then gradually lowered the die and sized a bit at a time and found no changes in bolt pressure.

Am I doing something wrong or is my chamber too long ?
Click to expand...

Expand the neck larger. You won't be able to close the bolt... then size gradually and test, size more and test... you will get to a point where the bolt will start to close.. then you are almost there... strip the bolt for a better feel.
 
powdergun said:
Just tried some new brass. Can't really feel any difference in bolt pressure. Will sizing lengthen in a bit so that it does put pressure ?

I expanded the neck then gradually lowered the die and sized a bit at a time and found no changes in bolt pressure.

Am I doing something wrong or is my chamber too long ?
Click to expand...

How much over the original diameter did you expand the neck/case mouth?

Measure a new piece of brass from the base to the datum line, now measure a piece of brass fired in your chamber.

What is the difference in the measurement?

It doesn't have to be to the datum line but some mid point on the shoulders taper, but must be the same for both.

The measurement from fired brass to sized brass should be 0.001 to 0.002" ideally.
 
guntech said:
Expand the neck larger. You won't be able to close the bolt... then size gradually and test, size more and test... you will get to a point where the bolt will start to close.. then you are almost there... strip the bolt for a better feel.
Click to expand...

I think I get where I got it wrong. I used the expander that was already in the die I guess I need a way to expand more.
Right now I don't have any die sets larger than 30 cal. Any tips on how to expand larger ?
 
Expand the neck, and then resize it partially until you can just close the bolt. This will create a false shoulder that will hold the case against the boltface, so that it will fireform to fit the chamber without the stretching that is causing the separations.
 
Guntech has explained three times, and Tiriaq once, so four times, above. Fifth time here: You need to expand your necks oversize. Buy an 8mm or 338 expander - run it through without sizing the brass - just open up the neck. Then start with your current 300 Win Mag die - set very long - say 3/16" from contacting the shell holder - size one case, try it in rifle - bolt will not likely close, try another after say 1/4 turn - try in rifle - and so on until you get so you can close bolt against some resistance. False shoulder has now positioned your case tight against bolt face and against shoulder neck junction. Load up and fire - it will blow out to fill chamber - use THAT LENGTH to resize the rest of your cases, and subsequent reloads!!! Or buy more new brass - that will work, too, for 3,4 or 5 reloads the way you are doing it.
 
Yup I got it. Just trying to determine the tool I need. I actually am not as thick as I appear. Or maybe it is the dementia kicking in lol...
 
Was an assumption made by some of us that not uncommon to just grab different die from drawer and "get 'er done". Been a while since I only had one die set on hand...
 
Might be able to buy just expander balls?? I use RCBS dies, mostly. I would swap out the expander stem from 8x57, or 338 Win Mag - have other choices, but one of those two will probably work? Not going to be re-sizing brass - the expander ball will be well below the die sizing dimensions - basically expanding the case neck on the up stroke of press die, then back out again. For a short term, will have wildcat "338-300 Win Mag", or "323-300 Win Mag" brass.
 
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