Firing pin spring strength

I just picked up a Model 10 in .223 off Gunbroker. Serial number puts it in 2003 year of manufacture. I was having about 50% light hits on the primers with failure to fire. All of them fired on the second try. These were all IMI Razor Core ammo. When I switched to hand loads with Wolf primers the problem went away. My Howa 1500 did not have this problem.
So my question is this; is it just that my firing pin spring tension is getting weak after 13 years? Could it be another issue? Is IMI ammo fitted with tough primers? Inquiring minds want to know.

Under normal circumstances there should be no problem with your firing pin spring. Dirt and sticky lubricants can be an issue. Take the bolt apart and clean the internals. Do not lubricate when going back together. Check firing pin protrusion for .035"-.044".

5.56 ammo should have harder military primers. 223 should not.

Those IMI rounds do have hard primers. I get the same thing with an Axis, although it has a .223 Wylde chamber and is safe to shoot those hot 5.56 rounds...

Don't blame the gun/spring before you check out the ammo. Too short (head space) for your chamber?? If you plan on using factory loaded ammo, you may have to live with it unless you reset the head space. If you roll your own, make sure you don't push the shoulders back too far and end up with the same problem "again". Keep it simple.:cool:

Had this problem with a Ruger RPR 223rem and Razorcore ammo. Check the primers to see if they are fully seated. Once I figured that out and seated them properly that cured a lot of it but I will still get an occasional FTF with the Ruger. My AR type rifles have no trouble with it.

Thanks everyone. Great suggestions all.