Finally figured it out (I think)...my occasional misfires.

[Ridgerunner665]

Ever since I got these two M70's I've had an occasional misfire that appeared to be a light primer strike...in both rifles.

One of the rifles did have a weak spring in it, I replaced the springs in both rifles....and had a misfire in my rifle the other day that caused me to miss a nice 6 point buck. I didn't actually miss, I just didn't get to shoot :x

I checked everything from chamber headspace to cartridge headspace to firing pin protrusion...bought new primers...everything...except the brass

I've been using a batch of Win brass that I bought from a guy on THR last year, it was new brass...I got the idea to check the seating depth of my primers, measured 100 rounds just now...94 of them were seated at .004"-.005" below flush...the other 6 were between .008" and .012".

I've never had this issue before but I'm pretty sure the primer pockets are too deep on a few of them...it has even happened a few times with cheap factory ammo (both Rem and Win)

M70's are more finicky with respect to this than a Rem 700 due to the difference in firing pin protrusion....055" for the M70, .060" for the Rem 700.

Not a problem...as long as one knows to look out for it...too bad I had to learn that the hard way, LOL.

And when I upgrade to the Tubb SpeedLock...I'll set the protrusion to .060" :mrgreen:

 

[Teknys]

That's a good find! My son had a reload not fire on a buck that he just put down but it was trying to stand back up.
It was in a Savage 16 Weather Warrior.
How did you measure the distance of the primer to base?

 

[Ridgerunner665]

The back end of most calipers has a rod (or something) that extends as the calipers are opened...its for measuring stuff like that.

 

[Oldtrader3]

That is why I use a hand priming tool. You can not put enough leverage on primers to make the primers go deeper than just touching and seating the anvil.

 

[Ridgerunner665]

This happened with hand priming too...I usually hand prime (RCBS), but have started priming on the Lee Classic turret...it happened with both methods.

 

[Oldtrader3]

You're trying too hard! :mrgreen:

 

[Ridgerunner665]

LMAO...that might be.

 

[SJB358]

Glad you sorted it out. Luckily, knock on wood, I use alot of WW brass and haven't had a missfire in any of my 70's. Something to think about though.

 

[Ridgerunner665]

Update to an old thread of mine...

Those misfires were caused by a bad sizing die...a Lee die.

Gunsmith confirmed through chamber measurements of die and rifle...the die was sizing the brass way too much...if not for a very tight head space on the rifle...it likely wouldn't have fired any of them.

Redding National Match die set cured this problem completely.

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[hubcap]

Very good info. I did not know oversizing would cause that problem. I will permanently store that info. Good job Ridge.

 

[Oldtrader3]

Wow, I bet you are glad to find that out? I really dislike getting dies out of headspace, of all things! Plus, problems like that will drive you crazy unless you try another die or know how much you are moving headspace datum!

 

[Ridgerunner665]

Yes sir...it was driving me nuts!

I finally gave in and took it to a gunsmith...took him just a few minutes to check the chamber, told me it was very tight, only .001" over minimum SAAMI head space...asked me to bring in the dies, checked them...they were something like .020" too short.

I spent a lot of money trying to figure this out (new brass, rounds fired, etc.)....and $20 trip to the smith was all it needed.

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[Oldtrader3]

Glad that it worked out for you and worth the $20 for peace of mind!