FN Winchester model 70 firing pin spring

[ZaneV]

Hey guys,
I’ve got a new model 70 in 416 rem mag, it’s had some issues with light strikes/duds on cci primers, and there isn’t a heavier firing pin spring available yet for the FN/portugal model 70.
I found a post somewhere where a guy with a similar Issue had used a modified Remington 700 shirt action firing pin spring to get a couple extra pounds of spring pressure. My dad had a couple on hand for his benchrest rifles, so I figured I’d give it a try.
The ID of the 700 spring is slightly smaller the Winchester spring, the stock Winchester spring had 0.010” clearance between the firing pin and the spring (this allowed the spring to bulge to the side a bit and rub the inside of the bolt which doesn’t help anything), the 700 spring had 0.003” between pin and spring but it was an inch or so longer. The wire diameters on both are 0.050” but the 700 spring had more tightly wound coils. I counted the coils on the stock spring (24 in my case) and cut the Remington spring to have 3 extra coils (27) and test fit, I could feel the spring binding when closing the bolt as the firing pin was drawn back. After some trial and error I ended up with 24.5 coils for it to operate without bind (it did operate with 25 coils, but I took another half coil off just to be safe. The result was 23.5 lbs of spring pressure vs 20 lbs on the stock spring. Attached is a picture of the stock spring vs the 700 spring on a primer strike only (no powder or bullet) to better gauge the depth of strike. I think it was a worth while mod, and maybe it’ll help someone else with the same issue.
Zane

 

[Ontario Hunter]

Why don't you try adding some tension to your existing spring? Simply stretch it manually to make it longer. I have done this with shotgun springs.

 

[358 Norma]

I may have to give that a try, thanks for the info.

 

[zephyr]

Had the same problem with a FN Win Mod 70 after about 200 rounds ...,,.
The OEM Spring I was told was a 24-25lb spring...
I purchased a Wolff extra power firing pin spring for a Win mod 70 that I believe was 30lbs... cut off the appropriate number of coils to the same length as original and installed ....

​

 

[ZaneV]

Had the same problem with a FN Win Mod 70 after about 200 rounds ...,,.
The OEM Spring I was told was a 24-25lb spring...
I purchased a Wolff extra power firing pin spring for a Win mod 70 that I believe was 30lbs... cut off the appropriate number of coils to the same length as original and installed ....

​

it seems to be a fairly common problem, I had my 1st FTF after about 50 rounds, And it’s been around 10% FTF since then. I think the factory springs were just weaker then advertised as I’ve seen a few guys says they were also in the 18-20 lb range.
How’s the bolt lift and safety operation with the 30lb spring?

 

[ZaneV]

Why don't you try adding some tension to your existing spring? Simply stretch it manually to make it longer. I have done this with shotgun springs.

I was going to try it, but I had these springs available and didn’t want to worry about them slowly shrinking back down over time.

 

[zephyr]

not a problem did not notice ...
My to FN Win's are a 400H&H and a 458 Lott
If I remember the spring was captured by a "C" clip my gunsmith put a small washer between the spring and "C" clip

 

[Ontario Hunter]

not a problem did not notice ...
My to FN Win's are a 400H&H and a 458 Lott
If I remember the spring was captured by a "C" clip my gunsmith put a small washer between the spring and "C" clip

A spacer. Hmm. Interesting. That should work.

 

[zephyr]

the intention of the small washer is to provide a better bearing surface between the spring's coils and "C" clip

 

[358 Norma]

Don't know if it's true or not but I've heard installing a Timney trigger makes the problem worse!

 

[ZaneV]

the intention of the small washer is to provide a better bearing surface between the spring's coils and "C" clip

I may add a washer to mine, a little more spring tension and surface area for the spring to sit against wouldn’t hurt at all.

 

[BlueFlyer]

I may add a washer to mine, a little more spring tension and surface area for the spring to sit against

The washer/spacer adds preload to the spring and increases the spring force. If the spring is loosing tension with use, it sounds like the heat treatment was NQR and it may loose more strength after time with a spacer.

 

[C.W. Richter]

Kudos on Hooke'ing your rifle up! Although 'have had several gun-related spring issues over the years (nearly all w/ a mauser-style action, incl. M70s and variants), my favorite correction was using triple valve springs in a heavily modified Buick 455 race engine (it prevented "valve float" at 7,000-7500 RPM). What a beautiful waste of time and money that was! I was Hooked.