M70 EW cratering primers

Ruger007

Ruger007

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I have recently started using my Winchester M70 Extreme weather in 264 win mag. Was new in 2017.

I have around 100 rds through it and now it is cratering all primers and has pierced 4 now.

Using new brass and N570 powder. Started at 65grs and worked up to 71.5grs with140gr Accubond.
CCI 250 primers.
During the work up i had none. Then started to get a faint crater at 71.5. Now a full on crater at my desired load of 67grs.
Tried some factory loads and it is doing it also.

Getting no other pressure signs, no sticky bolt, primers are nice and round on the edges, no extractor marks. Nothing. Speed at 67grs is 3175

Been reading that this could be a headspace issue? Or a weak firing pin spring?
I have been using new brass so haven't been able to adjust for that yet.

Any ideas? Or is it a send to Winchester issue?

Left was 71.5grs,. Middle is 67.5, right is 67.
About 30 rounds difference
Pierced the last 3 in a row at 67 and one factory winchester load.

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Try handloads with once fired brass neck sized or barely bumped.
Pull the bolt apart, clean the pin and examine it. Something easy likely.
My 2 cents worth
 
Something probably going on with the pin/protrusion.
On second thought the belted mag case headspaces off the belt so that shouldn't be an issue.
 
Just FYI if it has a shoulder you should be using it. Sizing to the belt every time is very hard on the brass. Of course with new brass it's not applicable. Also doesn't explain why factory ammo is doing it. You said the pin looks fine, how about the FP hole at the bolt face?
 
The hole looks good. I have no real way to measure such a small hole. I took the pin out and put it in from the front. A wouldn't say it tight.
 
Try removing the firing pin group and check clearance when inserted from the front. Could be an enlarged hole in the bolt face which is allowing flow. Sometimes a stronger firing pin spring will help or if hole is enlarged might need bushed.
 
I use a uniforming tool to get them to seat just under flush. I always double check at priming. Run my finger over them. Plus sit them on the table and check for rocking.
 
OP,
Clean the carbon "Donut" out of the leade/free bore of the chamber & pressures will stabilize.

Mic the necks of loaded rounds & fired brass to ascertain that .004"minimum neck expansion has occurred during firing.
If not,turn the case necks.

The firing pin hole in the bolt's breech face is slightly oversized as are all Winny's.
(bush it)
 
Did some measuring.
Bolt hole is slightly bigger than a #43 bit. .0890
Pin is .080

So about .009-.010

Loaded case necks. .2895
Fired case necks. .3000
 
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Took a while. Got a response from Winchester. Apparently a weak firing pin spring. They want me to send in the whole gun to a warranty center. I would rather not send the whole gun. Where can I get a better spring?
 
Wolff gunsprings. I have used the 30# striker spring in the older model 70's. Iirc I had to cut it down a bit for the newer model 70's.
 
You can order direct from Wolff, pretty expensive for a single spring though. Winchester's warranty center may sell you an OEM spring if you ask. I haven't ever dealt with them myself.
 
Pierced primers...

Is actually incorrect terminology unless the firing pin is so sharp it actually pierces the primer..

What occurs when you have primer failure as this, is the primer blows out a piece of material into the firing pin hole... usually due to a weak firing pin spring... it starts with cratering primers and then a piece of the primer blows out.

It is not a pierced primer...
 
Most gunsmiths should have a spare striker spring collection, the new M70’s have a shorter spring compared to the older ones. This will help you as an older spring can be cut down a bit, still fit and increase tension

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That is what is happening. A bit of Google and this seems to be a problem with a few M70EW. Just not having much luck locating a new spring. In Canada
 
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