primers backing out...........

snooker

snooker

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I've been reloading for over 30 years-----doesn't mean I always done it right----just always done it my way!
My son purchased a Rem 700 in SS, (pretty rifle), in 270 Win. He bought 3 boxes of Federal ammo, we shot & chrono'd some, averaged 3034fps (130 gr), I was impressed. I reloaded some of these once fired cases using H414 powder--48 grs. And a speer 130 gr bullet. Chrono'd at 2765 fps. 90% of the primers backed out on average 12 thousands of an inch. Never experienced this before. What is causing this?
Thanks in advance......
Dave.
 
Did you FL resize the brass? If so, it could be that the chamber is a little longer and the cases didn't headspace well. One common cause of backed out primers is when the case is off the bolt face, the pressure causes the case to grip the chamber walls, the pressure pushes the primer back against the bolt face, and the case will often stretch back and kind of suck the primer back in again. If the pressure was too low it might have gripped the chamber but not stretched back. The load you mention is fairly low pressure; only ~37k psi based on QuickLoad (only an estimate) where as a 270 is rated for 65k psi. A stiffer load might fireform the cases better.

Either way, I would guess your shoulder is set too far back. I would either fire-form and neck size or FL size with a finely adjusted die so the shoulder is set back just far enough to allow for easy chambering without being set too far back. This can be done with a trial-and-error method but is most easily done with special measuring tools that measure the head to the shoulder.

Generally you want the case against the bolt face and for them to not stretch backwards as this can eventually cause case head separation if it happens enough or to an extreme enough degree. If the cases were fireformed and neck sized, there is something odd happening.
 
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Did the primers did not back out in the factory ammo? If not, you are sizing the brass too much which pushes the shoulder back, and creates an excessive headspace situation.

The good news is, your loads are not creating enough pressure to stretch the brass. :)

Screw the sizing die up half a turn, and try to chamber an empty case. If it won't chamber, turn the die in a bit at a time until the bolt will just close on the resized case.

Load and go to the range again.

Ted
 
I did full length size the cases, I generally avoid neck sizing. I suppose I might have bumped the shoulder back a little too much. Next sizing I'll try not to touch the shoulder and see if that helps........thanks
 
Thanks lutnit, makes sense. Hodgdon reloading data site estimates the pressure at 50,400psi. I believe I've sized them a little too much.
 
Andy said:
That's a classic low pressure sign. Your low MV reflects that. Add 3-4 grs and it will go away.
Click to expand...

This!! Primers have backed out due to too low a pressure to cause the case to move back to the boltface on firing.

These cases may develop a weak "ring" just ahead of the solid head. Be sure not to resize these cases too much, as has been suggested.

Regards, Dave.
 
When a primer fires, it pushes the case forward, the shoulder back and the primer backs out. Then as pressure builds, it pushes the case back onto the bolt face and the shoulder re-forms.

If the load is too mild, the second part does not happen and you see stage one, with the primers backed out.
 
snooker said:
I've been reloading for over 30 years-----doesn't mean I always done it right----just always done it my way!
My son purchased a Rem 700 in SS, (pretty rifle), in 270 Win. He bought 3 boxes of Federal ammo, we shot & chrono'd some, averaged 3034fps (130 gr), I was impressed. I reloaded some of these once fired cases using H414 powder--48 grs. And a speer 130 gr bullet. Chrono'd at 2765 fps. 90% of the primers backed out on average 12 thousands of an inch. Never experienced this before. What is causing this?
Thanks in advance......
Dave.
Click to expand...

From the Sierra manual.

primers_zpsbfdd1418.jpg


The primer below has backed out of the primer pocket by the exact amount the case was made shorter than the chamber. Meaning you over resized your cases and pushed the shoulder of your case back .012 shorter than your chamber length. Normally on a bolt action rifle you only bump the shoulder back .001 to .002 shorter than chamber length, on a semiauto its .003 to .006.

HEADCLEARANCE-a_zps1a9a1011.jpg


Example below, your cases only need to be .001 to .002 shorter than the red dotted line. You are pushing (bumping) them .012 shorter than the red dotted line and over resizing your cases. This over resizing will cause your cases to "STRETCH" excessively and have case head separations.

shouldersetback_zps59bf1b04.jpg


If the chamber pressure is not high enough the primers will always protrude from the rear of the case. When the chamber pressure reaches the elastic limit of the brass the case will stretch to meet the bolt face.

HeadClearance_zpsf30a3af1.gif




A few suggestions.

1. Read the front part of your reloading manuals, they have a ton of information in them.

2. I see that you have never made a workup load for any of your rifles starting at the suggested starting load. If you would have started low and worked up you would have seen the primers gradually become flush with the base of the case as the chamber pressure is increased.

With a workup load your primers would have looked like below as the pressure increased, the last two primer are showing high pressure.
Know thy rifle, make a workup load and "learn" about your rifle and learn how to read pressure signs.

pressuresigns_zps50637610.jpg
 
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