Brass/dies issue or excessive headspace?

[SightedIn]

So my 18" JP barrel/bolt with about 1.5k rounds on it has started blowing head cases on an all to regular bases.
It did this every once and a while but only with cases that over 5-6 firings on them and were somewhat hot loads so just assumed the brass was beyond its life.
But lately its had case head seperations on brass with only 2 firings and standard loads on a regular basis.
Checking with a headspace comparator my fire cases are all 1.211, with sized cases down to 1.199. That seemed like a crazy amount of bump so i started using a different (new) die, a Forster. Lo and behold, the Forster sizes them to 1.199 also. And they fire form to 1.211 as well.
.012" bump?
Did my barrel/bolt suddenly gross headspace and so this brass is allolwed to grow .012" on firing?
Or am i missing something on this die/brass?
I dont have a go-no guage for grendel either
Maybe if someone with a 350 bushing can headspace their fired hornady brass and chime in

p.s. i dont have an other gr barrel chamber to compare to right now myself, sold my other build to a friend who moved to Texas. I know, i suck for selling a gun

[A5BLASTER]

So my 18" JP barrel/bolt with about 1.5k rounds on it has started blowing head cases on an all to regular bases.
It did this every once and a while but only with cases that over 5-6 firings on them and were somewhat hot loads so just assumed the brass was beyond its life.
But lately its had case head seperations on brass with only 2 firings and standard loads on a regular basis.
Checking with a headspace comparator my fire cases are all 1.211, with sized cases down to 1.199. That seemed like a crazy amount of bump so i started using a different (new) die, a Forster. Lo and behold, the Forster sizes them to 1.199 also. And they fire form to 1.211 as well.
.012" bump?
Did my barrel/bolt suddenly gross headspace and so this brass is allolwed to grow .012" on firing?
Or am i missing something on this die/brass?
I dont have a go-no guage for grendel either
Maybe if someone with a 350 bushing can headspace their fired hornady brass and chime in

p.s. i dont have an other gr barrel chamber to compare to right now myself, sold my other build to a friend who moved to Texas. I know, i suck for selling a gun

No your not adjusting your die correctly and your over working your brass and running to hot of a load.

You have the comparator, back the die out and slowly adjust it back in. Stop when it bumps the shoulder 3 to 4 thousands.

Just because the instructions say to make it touch the shell holder doesn't make it right.

[SightedIn]

Forgot to mention i did try adjusting the die last night but i had issues there too. No matter how carefully i screwed the die in or out ( like a degree at a time) it would either bump the cases too much ( well where it always was really at 1.199) or not enough, just like .001? or none.
Maybe I was too tired and missed something
I have another 20 or so fired cases though i?ll keep trying with the die adjustments. The tiny increments im turning it must still be too much
Let you know

[A5BLASTER]

Forgot to mention i did try adjusting the die last night but i had issues there too. No matter how carefully i screwed the die in or out ( like a degree at a time) it would either bump the cases too much ( well where it always was really at 1.199) or not enough, just like .001? or none.
Maybe I was too tired and missed something
I have another 20 or so fired cases though i?ll keep trying with the die adjustments. The tiny increments im turning it must still be too much
Let you know

I'm useing a foster full length sizing die myself.

Raise the ram to its highest point, screw the die in till it just kiss's the die. Now back it out a full turn. Measure a case and try to size then remeasure.

You want too thread the die in, in like 1/16 or less at a time. Until you get the correct bump back, then lock the die down.

Couple of questions.

What press?
What shell holder?
What case lube?
What comparator?

Just to be sure you have the correct parts.

[FLshooter]

What kind of powder,how much and bullets?

[SightedIn]

I'm useing a foster full length sizing die myself.

Raise the ram to its highest point, screw the die in till it just kiss's the die. Now back it out a full turn. Measure a case and try to size then remeasure.

You want too thread the die in, in like 1/16 or less at a time. Until you get the correct bump back, then lock the die down.

Couple of questions.

What press?
What shell holder?
What case lube?
What comparator?

Just to be sure you have the correct parts.

Got it, will do

Lee challenger single stage
Hornady shellholder
Alcohol/lanolin mix lube 12:1
Hornady comparator and bushing

[SightedIn]

What kind of powder,how much and bullets?

Typically 28.0 grs of 8208xbr with hornady brass/450 primers shooting 107smks

[A5BLASTER]

Got it, will do

Lee challenger single stage
Hornady shellholder
Alcohol/lanolin mix lube 12:1
Hornady comparator and bushing

Is it the very thin aluminum C style Lee press? If so that is the problem right there.

The press is flexing and that is what's giving you the problems and over sizing your brass.

I have one of the Lee challenger press's. It's made from aluminum and has a C shape.

I use to use it for decapping and one time ran some lapua brass through it in my hornady resizing die and it caused some problems like that. Oversized and undersized brass.

Luckly I caught it before I tryed to load them.

[Klem]

Sightedin,

Sorry to hear about your head separations but it sounds like a quick fix.

You are bumping your cases back too much. From 1.211 back to 1.199 is a .012" bump...Way too much stretch going on each time it fires. What's happening is called incipient case separation. 'Incipient' means gradual, over a number of firings and finally splitting at the weakest part which is in the middle of the case.

For an auto loader the best compromise of stretch to guarantee reliable cycling, but with the minimum stretch to maximise case life is .003". For a bolt gun it can be .001" or even no bump. Follow A5's advice with backing the die out and then working slowly in 1/8th turn at a time until it starts bumping and lock it when it gets to .003".

My initial stretch is .012" from new unfired Lapua brass. But, from then on they only get bumped .003" and so last many firings before being discarded. The Grendel SAAMI blueprint allows for up to .017" stretch however that is for a first firing only and doesn't take into account reloading the same case again. If you stretched it .017" a second time it would probably come apart, certainly by the third firing.

How hot your loads are might exacerbate all this but not as much as the stretch itself.

You don't need GO/NO GO gauges. Your comparator on a set of calipers is fine.

Depending on the brand of brass some cases will have more spring-back than others. This means you will never get exactly ,003" bump for every single case you size. Some will be .004" and a few .0025" so it's more a case of averaging the .003". Your Lee C-press is not the best but it still should be OK to load reliable ammunition. I doubt if this is the problem.

Doesn't sound like anything else is wrong with your bolt, dies or chamber. You are just bumping them back too much.

.

[Mark611]

Agreed! My Hornady B 350HSG, shows a Factory 123ELDM Black @3.204 un fired case out of the box, same case fired from the same box of ammo is @3.210 so were talking 6k of shoulder movement in my chamber, I have a Sanders 6.5Grrr barrel, I reloaded some of these case and pushed the shoulder back to the factory length of 3.204, which may have been to much, IMO I should have went to 06 or 07, but my next batch of loads I will try the those lengths to see if it locks up, my brother has the same barrel as I do, he bumps his back 4k and gets excellent results using the Hornady brass, I have checked several cases and these numbers are consistent, I hope this helps

[SightedIn]

Is it the very thin aluminum C style Lee press? If so that is the problem right there.

The press is flexing and that is what's giving you the problems and over sizing your brass.

I have one of the Lee challenger press's. It's made from aluminum and has a C shape.

I use to use it for decapping and one time ran some lapua brass through it in my hornady resizing die and it caused some problems like that. Oversized and undersized brass.

Luckly I caught it before I tryed to load them.

I believe it is aluminum, but its not C shaped, its continuous all around, sort of a square shape

[Mark611]

That's an O Block type press, and it should not flex, if you don't have any movement in ur die or ram and ur die is set up correctly? the problem is probably not in ur press IMO

[LR1955]

I believe it is aluminum, but its not C shaped, its continuous all around, sort of a square shape

SI:

Your JP rifle will not all of a sudden lose its headspace and unless you can physically move the barrel around with you hand -- look at your press and your lube.

Like A5B, I suspect the Lee press is giving you too much spring back and it is causing some real inconsistent amounts of pressure on your brass. I too have a Lee press and I use it for simple things like decapping or pulling bullets. I would trust it for sizing straight walled cases but not for any sort of sizing that needs any pressure like bumping does. Been there and done that with a Lee press.

Also, if your lube is home made it may also be the problem. I have found the home made spray lubes to be inconsistent and you could be getting an inconsistent amount of lanolin on the necks. That can cause huge differences in headspace when bumping.

LR55

[Mark611]

LR55, that was goin to be my next suggestion, to ask how much of that lube has been used in that die? if a lot then it may need to be cleaned out for excess build up, I also use that type of lube mix, on some of my brass, it works well, but ur dies do need cleaned out once in awhile!!

[Klem]

Guys,

Before we start looking at exotic reasons can we not look at the obvious first...His cases are stretching 0.012" each time. His ammunition is too small for the chamber; too much headspace.

And the most common reason for this is that the die is screwed in too far. Reloaders faithfully follow manufacturer instructions and screw the die in until it touches the shell plate. They end up with an arbitrary amount of case stretch that will never maximise the case life. The alternative is that manufacturers expect reloaders to understand headspace and own tools like comparators, which on this forum we take for granted. Screwing the die in till it touches the shell plate is OK for the majority of chambers that are reamed somewhere in the middle of SAAMI specs, but 'Sightedin' has a chamber machined on the generous side. His cases are stretching .012", Very similar to my Lilja group-buy barrel which is 0.011". Our first firing of new brass or factory ammunition will always be a long stretch; but after that with only a .003" bump everything should be tickety-boo.

Or, he can swap his bolt out for a 0.125" and hope that the .001" headspace is enough for reliable cycling. He could even screw his die in further if he had a 0.125" bolt.







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