Case head seperation

[jsthntn247]

I just trashed a couple hundred Lapua 223 cases after 4 firings. I had one separate on me which got me to looking at the rest of them. Some had no signs, some had light discolored lines near the case heads but not detectable cracks, and some had cracks you could feel with your fingernail. I use a redding type S die and have measured my shoulders when FL resizing to only bump 2-3k when sizing. I recently checked my comparator with the method of removing the firing pin assembly and chambering, sizing, chambering, sizing until no resistance is felt from the case and the numbers match what I have been bumping back to within .001, so it's not an over bumping shoulder issue. Could it be that my die is squeezing the cases too small in diameter near the datum line and causing this issue or something else? This is my ftr rifle chambered with a PTG match reamer.

 

[Jdne5b]

What is the base-to-shoulder measurement difference between a new piece of brass, and once/twice fired?

 

[mikecr]

Well, are you squeezing the cases a lot?
Are there high chamber clearances w/resp to your sized ammo?
Do your cases often need trimming?
Do you keep the chamber/cases clean/oil free?
Is the 2-3K bumping from actual interference fit, or added to a number recorded?
That is, what are you setting actual head space to?

 

[chuckshooter]

most of the time there only one answer to this, headspace. I know you said it is within .001, but check again. put scotch tape on the back of the case one piece at a time and chamber until you can't close the bolt. then measure and let us know.

 

[BoydAllen]

First of all, IMO the dimension that you bump to should be based on a case that was shot neck sized with warm loads until the shoulder to head dimension stabilized at a maximum value......OR if you are forced to bump based on the measurement of once fired brass (again, fired with a stout load) you should first set your FL die so that sized cases have the same shoulder to head measurement as fired, with the understanding that the fired case that you measure should have its primer removed or reseated well below flush before the measurement is taken. It generally takes more than one firing for a case to reach its maximum shoulder to head dimension. After one firing there is clearance in that dimension so bumping after one firing is not where you want to go. Certainly, if you set the die not to bump you can verify that that setting will work by chambering the case in your rifle. If you have issues relating to consistency of bump, going to more bump may not be the best way to deal with that. I like to set bump to .001 for critical applications and if I have issues with consistency use things like annealing or setting up to toggle slightly at the preferred dies setting to deal with it.

 

[jsthntn247]

What is the base-to-shoulder measurement difference between a new piece of brass, and once/twice fired?

All of these measurements were from a Hornady headspace gauge and Mitutoyo calipers. 1.255-1.265 new. 1.257-1.2585 on the first firing (I only neck size from the first to second firing) then 1.260 on all firings after that.

 

[jsthntn247]

Well, are you squeezing the cases a lot?
Are there high chamber clearances w/resp to your sized ammo?
Do your cases often need trimming?
Do you keep the chamber/cases clean/oil free?
Is the 2-3K bumping from actual interference fit, or added to a number recorded?
That is, what are you setting actual head space to?

Chamber and barrel cleaned after every match. Cases grow .001-.003 after firing then sizing. I'll measure the body clearance when I get home to see what those are compared to the brass fired in a match Saturday. On my headspace insert all fired brass after the second firing measures 1.260 and I bump back to 1.258. I came to this number by taking a fired piece of brass and sizing to 1.260... still tight when chambering , 1259......snug but not tight, 1.2585..... handle drops freely with a hint of contact,. 1.2580...... no contact when chambering, handle drops freely.

 

[mikecr]

Is your primer striking so strong as to further bump shoulders?
I've heard of this, none of my guns have ever done it.
But you could check it by firing a primer in an empty case and get before/after measure.

 

[brantfredrickson]

In addition to all that has been stated, measure the case head after its been fired, then after its been full length sized. My experience was the cases would come out of the chamber at .4725 and out of the body sizing die at .4700. I had a enormous factory chamber and a small body sizing die. I got case head separations in about thirty firings. And my headspace was .000 to .001.

 

[JFM33]

What is the measurement for unsupported case?
Is the bolt a coned faced ?

 

[Homerange]

I just trashed a couple hundred Lapua 223 cases after 4 firings. I had one separate on me which got me to looking at the rest of them. Some had no signs, some had light discolored lines near the case heads but not detectable cracks, and some had cracks you could feel with your fingernail. I use a redding type S die and have measured my shoulders when FL resizing to only bump 2-3k when sizing. I recently checked my comparator with the method of removing the firing pin assembly and chambering, sizing, chambering, sizing until no resistance is felt from the case and the numbers match what I have been bumping back to within .001, so it's not an over bumping shoulder issue. Could it be that my die is squeezing the cases too small in diameter near the datum line and causing this issue or something else? This is my ftr rifle chambered with a PTG match reamer.

For 223 you can mostly NS especially if you're not loading hot. Most of my range find once fired 223 Hornady brass is at 20+ firings and never FL sized or annealed but yes there is some minor camming when closing the bolt but if you keep a little lube on the lugs there'll be little risk of galling. Rem Model 7, 700 action, Lee collet dies. Working brass is to be avoided if possible.

 

[Dos XX]

Turn your scale down?

 

[ireload2]

It has to be over bumping. You need to form cases that drag slightly when the bolt is closed.
Then bump .001 more.

If you bump from a case that does not drag you have no idea how much too short the case is.

In addition you may have stretched the cases some on the first shot. Some factory ammo and brass may permit .004 to .010 stretch of the case on the first shot.

 

[billlarson]

Too much headspace...........????????
bill

 

[Richard Coody]

I just trashed a couple hundred Lapua 223 cases after 4 firings. I had one separate on me which got me to looking at the rest of them. Some had no signs, some had light discolored lines near the case heads but not detectable cracks, and some had cracks you could feel with your fingernail. I use a redding type S die and have measured my shoulders when FL resizing to only bump 2-3k when sizing. I recently checked my comparator with the method of removing the firing pin assembly and chambering, sizing, chambering, sizing until no resistance is felt from the case and the numbers match what I have been bumping back to within .001, so it's not an over bumping shoulder issue. Could it be that my die is squeezing the cases too small in diameter near the datum line and causing this issue or something else? This is my ftr rifle chambered with a PTG match reamer.

you need reloading lessons. find someone who knows what they are doing to show you the fundamentals before you hurt yourself.

 

[JohnKielly]

you need reloading lessons. find someone who knows what they are doing to show you the fundamentals before you hurt yourself.

I'm concerned. What he said in the latter part of his post is about what I've been taught works. Where's the isssue with that method of test sizing?

 

[Highpower-FClass]

I'm concerned. What he said in the latter part of his post is about what I've been taught works. Where's the isssue with that method of test sizing?

Agreed, it sounds like jsthntn247 is following the commonly prescribed fundamentals, does not seem to be anything wrong with his process.

jsthntn247, the only thing that seems a bit odd is your headspace measurements. I also use mitutoyo calipers + hornady gauge and my 223 cases measure around 1.460 fired. Are yours really 1.260? If so, perhaps we are using different inserts with the hornady comparator. I am using the one that says 'A330'.

 

[chuckshooter]

in post #7, you say after 2nd firing basically the brass is to tight to go back in? I think the issue might be too hot of a load. how much bolt lift after firing? do the cases extract easily? and what is the load? the best cases in the world can not take over pressure for long.

 

[spife7980]

Agreed, it sounds like jsthntn247 is following the commonly prescribed fundamentals, does not seem to be anything wrong with his process.

jsthntn247, the only thing that seems a bit odd is your headspace measurements. I also use mitutoyo calipers + hornady gauge and my 223 cases measure around 1.460 fired. Are yours really 1.260? If so, perhaps we are using different inserts with the hornady comparator. I am using the one that says 'A330'.

I just did some 223 lapua sizing last night and got the same 1.460 number on my fired brass as you with the same equipment.

 

[Turbulent Turtle]

Chamber and barrel cleaned after every match. Cases grow .001-.003 after firing then sizing. I'll measure the body clearance when I get home to see what those are compared to the brass fired in a match Saturday. On my headspace insert all fired brass after the second firing measures 1.260 and I bump back to 1.258. I came to this number by taking a fired piece of brass and sizing to 1.260... still tight when chambering , 1259......snug but not tight, 1.2585..... handle drops freely with a hint of contact,. 1.2580...... no contact when chambering, handle drops freely.

I worry about the numbers you quote. As has been stated above, it should be something like 1.460 to the datum line. If you use the Hornady inserts on your caliper, make sure you zero it with the insert touching the caliper branch and then measure from there. If you still get 1.260 or similar, you have a real issue.

Also, do you F/L resize your virgin brass?