Case head separation.

[zb338]

I have seen that condition many times with people shooting belted magnums
such as the .300 Win. mag and 7MM mag. People set the dies up to full length
size the case but push the shoulder too far back.
Zeke

 

[dennisinaz]

I've never read or seen this being a problem before. Do you by any chance have an excerpt from the book? I'm curious to know more.

How much variation are we talking? Is it only a problem between different mfg of brass? Or is the case to case variation enough to cause problems?


I only use one type of brass and lot per cartridge. When my brass changes, all my settings change. Maybe I've just been getting lucky?

I will look tonight.

 

[JimmyCP]

I have seen that condition many times with people shooting belted magnums
such as the .300 Win. mag and 7MM mag. People set the dies up to full length
size the case but push the shoulder too far back.
Zeke

Yep with multiple cases doing it that's probably what's going on. Head space buddy!

 

[Garry J]

Go to your Automotive supplier and buy a product called plastigage it's used to check clearance on cranks and camshafts between them and the bearings you can put this on the back of your shell and close your bold and see what the clearance between the bolt face and the base of the cartridge

 

[dennisinaz]

I will look tonight.

"Metallic Cartridge Handloading pursuit of the perfect cartridge" M.L. McPherson Safari Press, 1st Edition.


Page 26, second paragraph down.

"For full- length sizing of bottlenecked cases, the only correct way to adjust the die (to achieve the most consistent full-length resizing) is to make sure the fully raised ram always causes the top of the shell holder to abut solidly against the die body."


In chapter 5 he discusses headspace at length ( double-pun not intended in this case}

He has a table with minimum and maximum SAAMI specs for chambers and cartridges. A maximum SAAMI chamber and minimum SAAMI case can result in >.015" headspace.;.003"-.006" is preferred for a hunting round. At the top of page 80 we read "...when using conventional dies, the only worthwhile, repeatable and precise method of adjusting headspace depends on the use of Redding Competition Shellholders..."


I talked to Mic about this extensively at a match that we shot together a few years ago. He said that the variation in the amount of resizing was substantial when simply leaving a gap between the die body and shellholder.

No need for neck sizing dies. Your dies are more than likely fine just set wrong.
Use { TDOT's post #27 suggestion}. Let us know what you find.
Good Luck

I don't agree. If my die is .004" from bottomed out, what am I missing out on? .004" at the base not being resized means nothing compared to the shoulder of the round being .004" short

variations in the cleanliness of the brass, amount of lube, hardness discrepancies temperature of the brass and die and just plain old QC of the cases has a significant effect on this. By bottoming the die body against the shell holder, you take all these things out of the equation.

Just think of seating bullets. Sometimes you get a bullet that seats hard or easy. Why?? Why, indeed? Case sizing is the same type of thing.

 

[dennisinaz]

Go to your Automotive supplier and buy a product called plastigage it's used to check clearance on cranks and camshafts between them and the bearings you can put this on the back of your shell and close your bold and see what the clearance between the bolt face and the base of the cartridge

I just re-read his headspace section and Mic McPherson recommends Scotch brand cellophane tape. I typically use blue masking tape. Add layers until it is tight, tear the tape off and measure it. You can buy plastigage if you want too.

 

[Calvin45]

Also, not a bad idea to run a go and nogo gauge if you have access to them.
Also, looks like 79gr is a hot load according to hornady. I am ignorant to the load data, just pointing out what you probably already know

i find myself thinking this must a headspace problem or something. Either that or the bullet is jammed hard into the lands and spiking pressure. I load the 225 eld in my .300 win mag on a compressed load of 79 gr 8133. Slightly slower burn rate than retumbo, but the prc has slightly larger capacity than the .300. I have no pressure issues let alone head separation.

 

[D Scott]

"Metallic Cartridge Handloading pursuit of the perfect cartridge" M.L. McPherson Safari Press, 1st Edition.


Page 26, second paragraph down.

"For full- length sizing of bottlenecked cases, the only correct way to adjust the die (to achieve the most consistent full-length resizing) is to make sure the fully raised ram always causes the top of the shell holder to abut solidly against the die body."


In chapter 5 he discusses headspace at length ( double-pun not intended in this case}

He has a table with minimum and maximum SAAMI specs for chambers and cartridges. A maximum SAAMI chamber and minimum SAAMI case can result in >.015" headspace.;.003"-.006" is preferred for a hunting round. At the top of page 80 we read "...when using conventional dies, the only worthwhile, repeatable and precise method of adjusting headspace depends on the use of Redding Competition Shellholders..."


I talked to Mic about this extensively at a match that we shot together a few years ago. He said that the variation in the amount of resizing was substantial when simply leaving a gap between the die body and shellholder.






variations in the cleanliness of the brass, amount of lube, hardness discrepancies temperature of the brass and die and just plain old QC of the cases has a significant effect on this. By bottoming the die body against the shell holder, you take all these things out of the equation.

Just think of seating bullets. Sometimes you get a bullet that seats hard or easy. Why?? Why, indeed? Case sizing is the same type of thing.

 

[D Scott]

This makes sense,,,, what would make more sense ,if you saw die makers include competition shell holders with the purchase of their dies,,,imho

 

[Mram10us]

Does the book explain why no gap is so important? We were talking about moving away .008".
My shell holder measured .107"
my bolt face measures .138"
That is a gap of .021" not including the gap from bolt nose to bolt nose recess of barrel (normally >.010")
I contend the shell holder does not have to touch.

 

[entoptics]

Does the book explain why no gap is so important? ...
I contend the shell holder does not have to touch.

I contend that eliminating distance variables would increase precision. If cam-over forces >>> than sizing forces, then you're eliminating backlash issues (i.e. the press stops at the same place every time).

I also contend that I've had a heck of a time getting sub ± 0.001 consistent set back, both with cam-over and without.

To summarize, I think there's more important variables to be concerned with in proper shoulder bumping, than if the die hits the shell holder.

 

[Gcan]

Had a 300 UM

So I just got my 300 prc built a few weeks ago and have been shooting factory hornady match 225s. I wasn't getting the accuracy I wanted so I got a die and started doing some work up. I found a load my gun really liked at 79 grains of retumbo I set oal to the same as the factory stuff. Shot a 3 shot at .20 on center. However when I loaded it a second time testing the speed I got a case head separation. The brass has only been good for 2 firings. Just wondering if anyone has had any issues like this. Maybe a bad batch of brass?

Had a carbon barreled rifle (not a Proof) in 300 UM. Was crazy accurate but started separating reloaded cases on 92 grains R25 180gr bullets. (Two piece separations) Then the gun fired on bolt closing while on a black bear hunt in NewFoundland.
Head space was .011" past the no go gauge. It happens. So I would start there.

 

[Vol1975]

So I just got my 300 prc built a few weeks ago and have been shooting factory hornady match 225s. I wasn't getting the accuracy I wanted so I got a die and started doing some work up. I found a load my gun really liked at 79 grains of retumbo I set oal to the same as the factory stuff. Shot a 3 shot at .20 on center. However when I loaded it a second time testing the speed I got a case head separation. The brass has only been good for 2 firings. Just wondering if anyone has had any issues like this. Maybe a bad batch of brass?

my 2cents
Pressure plays a factory more than anything. My 2 case head separation failures example. Over 30 years reloading.
Running little high pressure and I was full length resizing on brass that was shot around its 5th time. I was only Pushing back brass With a FL die approx .002 back on shoulders and .002 ths above the belt. I was just bumping things back just enough to get the bolt to close easy.
Anyway what I found is old brass or in your case possible a bad piece was excellerated more than likely by pressure and the way a FL die work. A FL die pushes the brass by pushing the brass back in place from the front to back.

Conclusion on what I did, I Made sure I shot lower pressure. Got rid of all old brass or cheap brass.
Brass is cheap compared to a new set of eyes or at least a piece of brass stuck in the rifle.

oh everything was checked on gun, etc etc.

 

[25WSM]

Bottoming the shell holder is not going to fix dirty brass, amount of lube or hardness discrepancies. Common sense says don't put dirty brass in your die. Too much lube will dent shoulders either way. Hardness variation will give you inconsistent headspace either way. Anneal your brass if this is the issue. Not touching the shell holder is removing a variable of applied pressure. My brass come out of my dies with less than a .001 tolerance because of brass prep. I use clean brass. I use the propped amount of die wax. I anneal my brass and they stay up in the die for 5 seconds. I've been around precision reloading for over 30 years. I have built precision rifles professionally for 30 yrs. So basically yes you can have your die touch the shell holder if that's where it needs to be to get correct setback. In most cases your die touching the shell holder is giving you too much setback so it needs backed off. Common sense.
Shep