Updated 9/13/21: Model 70 firing pin springs

[Adam in WI]

I've searched the interweb, and emailed Wolff and Tubb (has not responded as of yet) looking for an explanation to what I thought should be a straight forward question. I have a (spanking) new Winchester Model 70 270 WSM that's having ~20% failure to fire with primers flowing into the firing pin hole. It seems to me that the striker spring is weak. I can (with safety off and firing pin assembly removed) rotate the shroud by hand between cocked and uncocked quite easily. With bolt fully assembled and bolt handle half way lowered and pulling the trigger, the spring does not have enough force to cam the bolt closed the rest of the way (all my other bolt actions will).

I thought I'd simply try a heavier firing pin spring, but according to Wolff they told me they do not make a spring for post 2008 FN built rifles. What's the difference? Do they mean FN branded rifles? Can use a post 64 Winchester fp spring? I know I should just send it back, but I don't want to deal with shipping and not having my rifle for a month if it's something I can fix for $10.

 

[Adam in WI]

The uncompressed spring measures .405 od .300 id and 4.4" long. I suppose now I can see if anyone lists dimensions online.

Before disassembly, I measured firing pin protrusion to be .055".

 

[gunsandgunsmithing]

If you haven't already...clean the bolt and firing pin assembly thoroughly and try again. Grease and cosmoline are common problem makers with new guns. fwiw.

 

[Will Henry]

They are a different spring and a different pin. The spring is shorter and the striker assembly is lighter. It would appear that your spring is too light, too short, or both. I think a striker spring, when cocked, should be compressed to where it is within about 30% of being fully compressed. To be honest, I'm just winging it with this number but I think I'm close. What is the diameter of the wire on your spring? WH

 

[Adam in WI]

. What is the diameter of the wire on your spring? WH

~.050"

 

[AlNyhus]

Before going any further, I'd test the spring weight on the factory unit and see where you're at.
You can test them easily with a bathroom scale. -Al

 

[Adam in WI]

Before going any further, I'd test the spring weight on the factory unit and see where you're at.
You can test them easily with a bathroom scale. -Al

Can you elaborate on the process?

 

[Adam in WI]

After reading here about the process; I reassembled the firing pin and spring before heading to the bathroom scale. It requires 18 pounds of pressure to begin moving the firing pin off of it's rested position. Measuring again with the pin compressed to approximately the same position as it would be cocked yielded a 20 pound reading.

 

[el pato]

I just replaced the spring on my older model 670 with a spring from Wolff.I was getting about 20% misfires also. I chose the 30 lb spring and it solved my problem. It took about 5 weeks to recieve it,12$.

 

[AlNyhus]

After reading here about the process; I reassembled the firing pin and spring before heading to the bathroom scale. It requires 18 pounds of pressure to begin moving the firing pin off of it's rested position. Measuring again with the pin compressed to approximately the same position as it would be in the cocked yielded a 20 pound reading.

Adam, sounds like you've identified the problem. For a hunting rig, something on the order of 28-30 lbs would be what I'd shoot for.

If a new replacement spring isn't available, you may have to start looking for a replacement using the original dimensions as a guide.

 

[Adam in WI]

Update: I ordered an original replacement from Numerich. It yielded about a one pound gain in the cocked weight. I shot 13 rounds yesterday with one failure to fire. Checking my new brass with a comparator shows it to be ~.010" shorter than fired brass from two different 270 WSM chambers. While I'm sure this isn't helping matters I still think this rifle should have a stiffer spring.

 

[AlNyhus]

If it was here, I'd make up a spacer to shorten the installed length of the new spring. -Al

 

[Will Henry]

Depends on the compressed length of the spring. There may not be room for much spacer. One can shorten the spring to increase the spring rate then install a spacer to make up the difference. The spacer goes at the top; next to the bolt sleeve. WH

 

[Adam in WI]

Update (again): Recent correspondence with Wolff reveals that they are in fact in the process of bringing to market springs for the new M70s with no promises as to when, but likely '22. Being the impatient bastid that I am, I did some snooping and what ifs and why nots. I found the spring dimensions to line up very closely to an M700 spring other than length.

So... Knowing less about springs than I do about reloading, I went ahead and ordered a 32 pound spring for a 700 short action. I figured I was going to be cutting a little off of it, I'd be better going slightly heavy right? Well, not exactly. I trimmed the approximately 1" difference off and installed it (real fothermucker BTW). I put it on the scales and got... 32 pounds. Hmm... So I put the bolt back together and run a few dry fire cycles. The difference in snap is noticable, but hard to quantify. The other difference immediately noticable is the increase in effort required to engage the safety. The real test will be if any primer has the stuff at this point to say no...