I recently started loading 6.5 CM with Magnum Small Rifle primers. However out of 20 rounds I had 3 that failed to ignite the first strike of the firing pin. They did ignite on the second or third strike. I was wondering if the firing pin spring may be the issue as it is at least 4 years old. I was able to get a replacement.

Just wanted to ask some experts if this could resolve this issue?

I won't be able to test it out for another week.

Here is a picture of the new spring(top) and old spring (bottom?

I'll chime in until the experts show up. Your replacement spring is longer of course but appears to be of slightly less diameter. Not too many springs will fail in 4 years of shooting. Maybe the OEM spring just gave up or was never optimal. The other thing to check is that your primers are fully seated. Not just seated but fully seated.

In any case, put the new spring in and see what happens. You can also try other ammo to see how consistent the problem is. Hopefully the new spring will get you past this problem.

Can you measure it at its compressed length? You need 24-28 lbs. Assemble the firing pin assembly without the spring, make sure it is free and not getting hung up or sticky in spots. FWIW, I could count on one hand the number of primers I had fail in the 30 years prior to the china virus. I have had double that many fail that were produced since 2020

I actually had some slight hangfires (maybe a tenth of a second) and one dud on my last trip out to the range. Using Wolf SRMP in a 6mm creed.

Here's what I would try, in this order:
Check primer seating depth
Check that powder is still good
Check flash holes
Change primers
Change firing pin spring
Check headspace

I'm currently on the change primers stage, just need to test my rounds. I'm also using the Wolf primers in my 5.56 loads and they worked out fine, so I think there's just not enough juice in them to really set off a big load of H4350.

Maybe relevant, maybe not...maybe 15 years ago I bought a few bricks of Wolf small rifle primers because availability of the usual domestic brands was getting spotty. I tried them in a wonderfully accurate 700 Classic in .223 (which I still mourn after selling it and then discovering I'd made a huge brass prep error causing my accuracy issues at a later date). I was able to get five-shot groups under 1/2 inch four consecutive times with that load in that rifle, using Wolf primers, but it seemed like I'd have a misfire or two out of every box of 100 primers. No other primer I ever tried in that rifle gave me such poor reliability OR such great accuracy. Odd experience, but true.

Steve, do you have pics of the primer strikes of those that did not fire?

They all fired on the second or third strike. And looked just like the ones that fired on the first strike.

So the primers were all good and ignited the powder.

I can only attribute this to light firing pin strikes.

They were all new brass and I checked the headspace and primer pockets before loading.

I believe they were all seated properly via the Dillon 550 I have used to load thousands of rounds with. But that was one of my first thought. I can usually tell if the primer is not seated correctly. Maybe my eyesight is not as good as it used to be .

I loaded up some with just the primer to test with the new spring. I'll post my results tomorrow

If they're going off on the second or third strike and the new spring doesn't fix it I would not call those good primers lol

Great news!!! The new spring did the trick. Fired 40 rounds today and not one failure.

I'm confident that that was the solution.

I was prepared to see if the primers were bad by loading some 5.56 rounds with the same primers in case I still had an issue. But turns out I didn't need to use them. But I did anyway just to have a fun day.