Home Forums Hunting & Shooting Gunsmithing Win 70 piercing primers

A friend of mine called me the other day and told me his pre 64 70 he was sighting in pierced a primer after the 4th shot. He thought the firing pin broke because the gun would no longer fire. He was shooting factory Hornady 130gr American Whitetail.

He carried it to a local smith and the bolt was taken apart to check firing pin. The smith said a piece of the primer was hung in the bolt keeping the pin from firing.

He called me and I told him something was up if it was piercing primers. I told him to have the headspace checked and the smith said it was fine.

He loaded up some reloads and after the fifth shot it pierced another primer. I asked him if the smith checked the pin protrusion and he said he didnt.

Any win 70 shooters ever run across this problem?

Need to check for a sharp point on the pin,it doesn't take much to poke a hole.

Ill tell him to check that.

I've seen it before, but somewhat rarely in the M70.. It's usually an issue with headspace, but a damaged firing pin can also be the culprit.

Protrusion should be .055 but no more than .060. If headspace is a bit on the 'generous' side it can cause a pierced primer. I've had factory barrels with headspace that allow the bolt to drop halfway before stopping on the NO-GO.. I don't like that on any rifle, but especially on magnums.. You don't state what chambering your friend's rifle is but the 130 gr bullet might indicate a .270.

An experienced M70 smith in your area should be able to diagnose the issue for you..

its a 270

There are two different but similar scenarios. A pierced primer is generally the result of a damage or misshaped firing pin tip. A blanked primer is the result of:
High pressure
A weak primer cup
An oversized firing pin hole in the bolt face
A lightweight striker
A weak striker spring or
A combination of these factors.
The pre-64 models have a smaller diameter pin than the post 64 models have and blanking is less common. However, it can happen that the hole can wear large (caused by a misaligned or bent pin)and leave too much of the cup unsupported.
If a primer pierces due to a weak or flawed primer cup, the tip of the pin is often flame cut which makes it more damaging to the cups of subsequent primers and makes repeated piercing more likely.
A rifle which is blanking primers will usually give some indication in the form of cratering on primers which do not blank.
When I have a riel which is doing this (whether piercing or blanking)I will first examine the firing pin tip for cutting, sharp edges, or any other damage and will shape and polish it to forma nice, smooth hemispherical tip.
I will the check protrusion which I like to have around .050" or so.
I will then gauge the firing pin hole to check diameter and clearance on the tip.
If the rifle is cratering primers, I may replace the striker spring with a slightly heavier rate of spring.
If the rifle still blanks primers. I might try different brands of primers. Often one brand or another will have a tougher cup and be more resistant to blanking.
If the rifle continues to have a problem, I'll bush the firing pin hole and reduce the tip diameter. This never fails but is a bit of a job.
What is difficult to explain is why one can have two rifle which are identical in all respects yet one will crater primers and the other will not. It can be quite frustrating.
One of my more memorable experience along this linje was with a 30/06 target rifle I had built on a post-64 action. This rifle worked well and shot great but suddenly started blanking primers about 20% of the time. This made it very difficult for me to fire a good ten shot string when I could expect a faceful of debris any time I pulled the trigger. After the first day of the match, I rushed home (sixty-five miles)and polished the tip. Steeped out to the range and got off three shots before getting blasted on the fourth. Put in a heavier spring. Same result. Decided I had not choice but to bush the bolt face and turn down the tip so I started to do so. Got the bolt face done and had just chucked the firing pin when the power went out! Nothing to do but wait so I did. At about 4 AM the 'fridge started up so I knew the power was back on. I went dowmstairs in my robe and slippers and finished turning the firing pin tip. No way to test so I tested at the match. It worked just fine and that action has never had another problem. I don't know why Winchester decided to go with the larger firing pin diameter but it was, in my opinion, a mistake. GD

Thanks greydog. Great answers.

The Winchesters I've seen have big diameter firing pins, the biggest I recall. If all else checks out, I would have the pinned turned to .0625" and the hole bushed properly.

I think we can all thank Stiller for the small pin diameter concept.

Maybeso but I don't think he anything to do with designing the P14 Enfield. The .062 diameter firing pin tip, along with the substantial mass of the striker, makes it almost impossible to blank a primer in a P14. The pre-64 pin is smaller than that on a post 64; by about .008" but the hole is often over-sized; usually due to wear from a misaligned pin. GD

Is your friend sure the primers were all seated deeply enough?

Factory ammo was piercing primers too.

Check you case lengths. An over-long case will extend into the throat which will restrict the case neck expansion and create incredible pressures, thus flattening or blowing primers. I've seen this very thing blow primers, extractors, and erode bolt faces, all for the lack of a Forster case length trimmer. Extreme copper fouling in your bore can produce similar results.

Forget all about case length, headspace, bore fouling, or what's for dinner. The problem is with the rifle and is probably with the diameter of the firing pin hole in the bolt face and may be worsened by a weak striker spring, too much protrusion, or a poorly shaped tip. GD

I seriously doubt that he is piercing primers, blanking them maybe.
A lot of people do not realize the difference.

Wow.

Wow is right. I would have fixed it and had it out hunting by now. GD

By all means, forget doing any common sense checks and safety measures. They are difficult and expensive, right? Just start at the easy stuff, like modifying your bolt face, firing pin, and spring. Greydog, you may well be correct in your suggested repair, but to suggest that safety advice be ignored is, well, foolhardy. A lot of people who seek advice on these forums may not have the safety habits that you have. Firearm safety is our first responsibility, then.... the sage advice about what fixed my rifle that one time that the failure happened to me. I don't question your knowledge or expertise. Don't ridicule mine.

GD forgot more about rifles in 1 minute than you have learned on the internet.

Let's see. You guys assume that no one knows anything about guns but your cronies on 24hcf. I don't question GD's knowledge, nor yours. I just get sick of you guys dismissing everyone else's suggestions out of hand. This is why Internet Advice has lost so much credibility. I am a gunsmith with over 30 years of experience and an excellent reputation in other places than a gun forum. Your assumption that I have ever learned anything from the internet is correct, as there is usually very little to learn from guys who spend all their time postulating and attacking people on gun forums. You are probably right that GD has forgotten more than I have learned from this forum, other than the cronyism and defensiveness of your ilk. I see you guys with 5000 plus posts and wonder when you gave time to work on or even shoot a gun. Rant over. Have a great day.

Please educate me. I'm not a smith.